Achieving Record External Quantum Efficiency of 10.14% in Non-Doped Single-Emissive-Layer White Light-Emitting Diodes Utilizing Hot Exciton Mechanism

Achieving Record External Quantum Efficiency of 10.14% in Non-Doped Single-Emissive-Layer White Light-Emitting Diodes Utilizing Hot Exciton Mechanism | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Achieving Record External Quantum Efficiency of 10.14% in Non-Doped Single-Emissive-Layer White Light-Emitting Diodes Utilizing Hot Exciton Mechanism Ping lu, Futong Liu, Hui Liu, Yichao Chen, Xin He, Zhuang Cheng, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4180968/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract White organic light-emitting diodes (WOLEDs) based on non-doped single emitter can promise convenient fabrication technology, absent phase separation, minimal color-aging, and good reproducibility for next-generation displays and lightings. However, the pure organic materials that could radiate intense white light are extremely rare, and the external quamtum efficiencies (EQE) of previously reported non-doped white OLEDs do not exceed 5%. Hence, the straightforward preparation of single white light-emitting molecules for high-performance non-doped WOLEDs remains a high challenging task. Herein, we design and synthesize four hot exciton materials, PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, which consist of anthracene, pyrene and imidazole functional groups. Based on the rational manipulation of intermolecular interaction and excited state property, PIAnPy and PyIAnPy display dual emission in the neat films originating from the monomer and excimer emission. Exploiting PIAnPy as a single emitter, a non-doped WOLED is fabricated with a record EQE of 10.14%, a maximum luminance exceeding 50000 cd m -2 and the Commission Internationale de L'Eclairage coordinates of (0.35, 0.26). Its EQE maintains as high as 9.80% at the luminescence of 1000 cd m -2 showing a very low efficiency roll-off. To the best of our knowledge, this is the best results of non-doped WOLEDs based on the single-component emitters reported to date. Physical sciences/Optics and photonics/Lasers, LEDs and light sources/Organic LEDs Physical sciences/Physics/Electronics, photonics and device physics/Photonic devices Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Lighting currently constitutes 15–28% of the electric power consumption in the world. With the initiatives to reduce illumination-related energy consumption and carbon emission, white organic light-emitting diodes (WOLEDs) have drawn great attentions as the desirable candidates to realize large-scale flat and curved panels in high-quality displays and energy-saving solid-state lightings. 1 They offer a range of attractive characteristics such as self-luminescence, free of blue light hazard, wide viewing angle, good flexibility and considerable power efficiency that rivals the performance of the point and line lighting source from fluorescent lamps and inorganic LEDs. 2–4 In principle, the device needs to exhibit emission spectrum continuously covering the whole visible region ranging from 400 to 700 nm to achieve white light. For this purpose, the reported high-performance WOLEDs usually consist of three primary-color (RGB) emitters or two complementary (blue and orange) emitters. In most cases, complicated device configurations are adopted to stack multiple emitting layers or mix various color chromophores into one emitting layer. In addition, excitons ratios have to be precisely manipulated to be formed properly on different emitters, and one or more interlayers are required to balance carriers as well as confine excitons within respective monochromic layers. 5–7 Albeit the success in improving the external quantum efficiencies (EQEs) and power efficiencies, such WOLEDs may suffer from several issues including complex fabrication procedure, inevitable phase separation, poor color reproducibility and variable CIE coordinates under different voltages. The noble-metal containing phosphorescent materials are often involved in the emissive doping system, which generally improve the device cost, give rise to environmental pollution, and impede the widespread commercialization of WOLEDs to a large degree. 8–11 To overcome these problems, a promising alternative strategy is to construct single-emitting-layer WOLEDs based on purely fluorescent materials, which can provide many advantages such as easier fabrication process, lower cost, free of phase separation and stable emission color. 4,12–15 Besides, the precise selection of complex host-guest system and fine-tuning the doping concentration which is essential in traditional WOLEDs will be unnecessary by using single molecule as the emissive layer, laying the foundation for the fabrication of simple and cost-effective non-doped WOLEDs. For the preparation of efficient materials suitable for the application in non-doped single-emitting-layer WOLEDs, the key point is delicate control of the molecular excited state. According to the Kasha’s rule, the fluorescent material radiates monochromatic light that originates from the lowest excited singlet level (S 1 ). 16 This will lead to the limited spectral bandwidths in common fluorescent materials. Noticeably, there are a few reports about addressing this challenge during the past decades by adopting excited-state intramolecular proton transfer (ESIPT) 17–19 , charge-transfer (CT) 20,21 , excimer 12,14,22–24 , room-temperature phosphorescence (RTP) 10,25,26 , delayed fluorescence (DF) 13,27–29 and other mechanisms 13 to endow the emitters with multiple excited state and accordingly enable white light emission. However, few of them can exhibit white electroluminescence (EL) under electrical excitation in OLEDs applications. 4,10 At present, only several non-doped WOLEDs have been reported to yield EQE of about 5%, approaching the limit of traditional fluorescent materials since only 25% singlet excitons are spin allowed. 12–14,30,31 Thus, developing the non-doped single-emitting-layer WOLEDs with EQE breakthrough the limitation of spin statistics remains a highly challenging task. In this work, we prepare a series of fluorescent materials PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, which constitute of imidazole derivatives (benzimidazole, diphenylimidazole, phenanthroimidazole, pyrenoimidazole) and polycyclic aromatic hydrocarbons (PAH, anthracene and pyrene) showing multi-excited states (Fig. 1 ). These compounds are designed in consideration of the following points: ( 1 ) Imidazole possesses a bipolar carrier transportation nature, and extending the structure of imidazole with rigid aromatic rings, such as benzene, diphenyl, phenanthrene and pyrene, could effectively enlarge the π-conjugation structure as well as molecular rigidity to exhibit intense blue emission in short wavelength region. 32–34 ( 2 ) Combination of PAH-based moieties of anthracene and pyrene initiate the formation of excimers between the excited state monomer and the ground state monomer, leading to a red-shift in emission spectra in long wavelength region. Moreover, the largely extended π-conjugation planes are conducive to the generation of abundant supramolecular interactions, such as hydrogen bonding, C-H…π and π…π stacking, which might regulate the aggregation state of the compounds and realize broadened excimer/aggregation emission. 35,36 ( 3 ) In our prior studies, it is found that materials with hot exciton mechanism provide high potentials to simultaneously achieve high-efficiency and low efficiency roll-off in non-doped device through the reverse intersystem crossing (RISC) channel from high-lying triplet excited states (T n , n > 1) to the singlet excited states (S m , m ≥ 1). 37–39 Anthracene and pyrene with delicate alignment of energy levels would be beneficial to induce the high-lying RISC process, showing high potential to achieve EQE exceeding 5%. 40 As a result, owing to the various energy alignments in short wavelength and long wavelength zone, the individual emission from imidazole-based chromorphores and PAH-based excimers could be obtained at the same time in PIAnPy and PyIAnPy, which eventually bring about a continuous electroluminescent spectrum close to standard white light. The resultant non-doped device incorporating PIAnPy as the active emitter is successfully fabricated, exhibiting white light with the CIE coordinates of (0.35, 0.26), the luminance over 50000 cd m -2 and the excellent EQE of 10.14%. Moreover, the device displays very low efficiency roll-off of 3.3% under the luminance of 1000 cd m -2 , which is the best result among non-doped single-emitting-layer WOLEDs. Whereas with a more extended π conjugation, PyIAnPy presents a much stronger excimer emission. PyIAnPy-based non-doped WOLED exhibits a stable emission approaching warm white light with a CIE of (0.40, 0.32) and a high EQE of 8.83%, which is also pioneering among single-emitting-layer WOLEDs reported so far. It is the first example that the efficient non-doped WOLED via the hot exciton mechanism can be fabricated. The state-of-the-art device performance demonstrates the great potential of this molecular design strategy in simultaneously achieving high efficiency and low efficiency roll-off for non-doped WOLED applications. Results and Discussion Synthesis and Characterization As shown in Scheme 1 , PhAnPy, DPhAnPy, PIAnPy and PyIAnPy were all conveniently prepared by a two-step reaction. The brominated product of PyAnBr was first synthesized through the Suzuki coupling reaction between pyren-1-ylboronic acid and 9, 10-dibromoanthracene, which was further treated with intermediates PhPIB, DPhPIB, PPIB and PyPIB to afford PhAnPy, DPhAnPy, PIAnPy and PyIAnPy in high yields. All the target products were purified by column chromatography on silica gel and sublimated under vacuum condition. The molecular structures were fully characterized and verified by NMR and mass spectrometry. The synthetic details were provided in the Supporting Information. The thermal property of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy were examined. As shown in Figure S5 (Supporting Information), PhAnPy, DPhAnPy, PIAnPy and PyIAnPy all exhibited high decomposition temperatures ( T d , corresponding to 5% weight loss) values of 473, 492, 500 and 505°C, respectively. The glass transition temperatures ( T g ) of PhAnPy, DPhAnPy and PIAnPy were recorded at 177, 192 and 160°C, respectively. Additionally, the high melting points ( T m ) of 333 and 362°C for both PhAnPy and DPhAnPy were observed. PyIAnPy showed no obvious exothermic or endothermic signals in the measurement cycle suggesting its high rigidity. Such high and tolerable temperatures indicated that they could retain amorphous morphology during vacuum thermal deposition process which was suitable for fabricating OLEDs by vacuum deposition technology. The cyclic voltammetry (CV) measurements were employed to investigate the electrochemical properties and estimate the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels of the emitters. As shown in Figure S6 , the HOMO/LUMO levels of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy were estimated to be -5.73/-2.97, -5.67/-2.89, -5.62/-2.84, and − 5.63/-2.86 eV, respectively, from the onset of the oxidation and reduction potential against the ferrocenium/ferrocene (Fc + /Fc) redox couple. Photophysical Properties The UV-vis absorption and PL spectra in THF solution with a concentration of 10 − 5 M were explored. As shown in Fig. 2 a, PhAnPy, DPhAnPy, PIAnPy and PyIAnPy displayed the similar absorption profiles dominated by multiple localized π-π* transitions originating from the combination of imidazole, anthracene and pyrene segments. The absorption peaks with fine vibronic structures at 350–400 nm were ascribed to the π-π* transitions of the core anthracene, while the higher-energy absorption bands at around 290–350 nm were assigned to π-π* transition from the pyrene moiety. Their optical bandgaps ( E g ) were calculated to be around 2.76 eV–2.78 eV. Under the excitation of a UV lamp, the compounds displayed very identical structureless emission with the maximum emission peaks in the range of 440–444 nm. They also showed high PLQYs of 60–79% measured by integrating sphere, and PIAnPy possessed the highest PLQY of 79% owing to the efficient radiative decay process. To deeply understand the properties of S 1 state, the solvation effects of these compounds were examined in various solvents. The PL spectra of PhAnPy, DPhAnPy and PIAnPy exhibited only tiny red-shifts of 12 nm, 12 nm and 13 nm as the solution polarity increased from hexane to acetonitrile, suggesting they possessed a locally emissive (LE) characteristic in the excited state ( Figure S8 , Supporting Information). According to the Lippert-Mataga equation, the dipole moments were estimated to be 5.67 D, 6.55 D and 6.88 D for PhAnPy, DPhAnPy and PIAnPy, respectively, further implying that the LE characteristic was dominant in the S 1 state of these molecules ( Figure S9 , Supporting Information). The situation was different in PyIAnPy. The emission peak of PyIAnPy showed a relatively larger red-shift of 26 nm demonstrating the stronger CT-state character from pyrenoimidazole to pyrene. PyIAnPy also displayed a typical two-section linear relationships in high- and low-polarity solvents, manifesting the LE-featured and CT-featured radiative transition, respectively. It was noteworthy that PyIAnPy exhibited single-exponential fluorescent decays in all the tested solvents ( Figure S10 , Supporting Information), indicating the LE and CT components were well integrated into the hybridized local and charge transfer (HLCT) state rather than simply mixed state. 41 The fluorescent spectra were measured in THF solution at 77 K ( Figure S11 , Supporting Information), and the corresponding energy levels of S 1 could be calculated to be 2.82, 2.74, 2.78 and 2.76 eV for PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, respectively. Nevertheless, no delayed emission spectra from phosphorescence were observed due to the low population and high non-radiative transition rate of T 1 state. To promote the production of the T 1 excitons, the classical PtOEP with a T 1 of 1.93 eV was adopted as a triplet sensitizer to populate the T 1 excitons through effective Dexter energy transfer ( Figure S11 and S12 , Supporting Information). 38 The new emission peaks around 677 nm appeared in the 5 ms delayed phosphorescence spectrum when compared with that of the pristine PtOEP solution, thus the T 1 energy levels of these compounds were calculated to be around 1.83 eV. Based on these results, the TADF mechanism could further be excluded because of the large energy gaps of 0.91–0.99 eV between S 1 s and T 1 s of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy. Different from the emission behavior in solution, all the compounds showed distinct emission spectra in the evaporated films (Fig. 2 b), PhAnPy and DPhAnPy exhibited bathochromic shift with the maximum emission peaks of 453 nm and 470 nm and large full-widths at half-maximum (FWHM) of 66 nm and 124 nm, respectively, due to the enhanced aggregation effect in the solid state. Particularly, PIAnPy exhibited bluish white light with the main emission peak at 466 nm and a weak emission band around 585 nm. PyIAnPy displayed a stronger white-light emission with two distinct peaks at 465 and 600 nm, which gave rise to a very broad emission band that covered the whole visible range extending from 400 to 750 nm. In order to eliminate phosphorescent interference, the PL spectra were further examined by altering the test condition from vacuum to oxygen. The similar results were obtained (Fig. 2 c), indicating that the triplet exciton barely got involved in the PL behavior. As shown in Fig. 2 d, the UV-Vis and PL spectra recorded before and after deposition were also consistent, implying that no chemical changes during vacuum deposition. To explore the origin of the white-light emission, time-resolved fluorescence of PyIAnPy in neat film state was measured (Fig. 3 a). The lifetimes for PyIAnPy were 1.94 ns for peak at 465 nm and 5.69 ns for the peak at 600 nm. The largely red-shifted PL spectrum and longer-lived species that emitted at 600 nm from the PyIAnPy film were in good accordance with the characteristic of excimer according to the previous reports. 36 The excitation spectra of PyIAnPy monitored at either 465 nm or 600 nm were very similar and matched well with the absorption spectrum (Fig. 3 b), which further confirmed that the excimer was originated from the common ground state and excluded the possibility of the formation of a new fluorophore. Accordingly, the assignment of this 600 nm peak in the PyIAnPy neat film to an excimer emission was reliable. Moreover, the PL spectra of PyIAnPy in THF solution at different concentrations were examined, and it was found that there was a new emission band appeared at the long wavelength of 580 nm upon the concentration of 0.01 M (Fig. 3 c). As the temperature was increased from 296 K to 500 K, the fluorescence intensity was gradually enhanced along with the almost unchanged fluorescence maximum (Fig. 3 d), supporting the thermally activated excimer formation. 12 PIAnPy also showed an excimer emission at 585 nm, but its intensity was much weaker and narrower due to a different packing of the phenanthroimidazole moieties in PIAnPy compared to PyIAnPy which could not generate an intense white emission. Crystal Structures The single crystals of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy were obtained via the temperature-gradient sublimation process. The PIAnPy and PyIAnPy crystals also exhibited dual emission with maximum peaks at 454 and 586 nm for PIAnPy, and 453 nm and 621 nm for PyIAnPy ( Figure S14 , Supporting Information). X-ray structural analyses were further performed to resolve the molecular packing of above four crystals. As displayed in Fig. 4 , PhAnPy, DPhAnPy, PIAnPy and PyIAnPy all adopted highly twisted molecular conformation, which could effectively suppress the intermolecular π-π stacking and ensure efficient radiative transition in solid state. In the PhAnPy crystal, two types of C-H…π interactions were observed between the pyrene plane and H atom on the adjacent molecule with the distances of 2.663 and 2.739 Å. The C-H⋯π interactions with distances of 2.753–2.763 Å and C-H⋯N (2.700 Å) hydrogen bonds were found in the crystals of DPhAnPy. Apparently, these weak intermolecular interactions contributed to stabilize the molecular structure, but the distances were not short enough in PhAnPy and DPhAnPy to generate the excimer emission. In contrast, the C-H···π interactions in PIAnPy were much stronger than those in PhAnPy and DPhAnPy with shorter distances of 2.501–2.728 Å because of the more expanded π-conjugation. In particular, benefiting from the further extended pyrenoimidazole structure as well as the enhanced rigidity of the whole molecular plane, PyIAnPy possessed the most abundant and strongest C-H···π interactions with distances from 2.409 to 2.824 Å between one pyrenoimidazole, anthracene and pyrene planes as well as one edge-ring hydrogen atom from neighbouring molecule, demonstrating that a two-dimensional intermolecular network were formed by the edge-to-face interactions and close stacking mode in the crystal, which facilitated the formation of excimer in the aggregated state. 12 More importantly, the multiple hydrogen bonds could further stabilize the π-stacking interactions and lock the molecular rotations. Meanwhile, the absence of obvious π-π interaction is conducive to attain high PLQYs of 73%, 68%, 78% and 63% in PhAnPy, DPhAnPy, PIAnPy and PyIAnPy crystals, respectively. Theoretical calculations To further investigate the relationship between molecular structures and electronic properties of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, the density functional theory (DFT) calculations were implemented. The optimized molecular structure and frontier molecular orbitals together with the corresponding calculated values were displayed in Fig. 5 . PhAnPy, DPhAnPy, PIAnPy and PyIAnPy all revealed nearly orthogonal geometries between the anthracene and adjacent units of pyrene/imidazole derivatives with large dihedral angles of 79–89°, which was well consistent with the single crystal structures. PhAnPy, DPhAnPy, PIAnPy and PyIAnPy had similar LUMO distributions, mainly localized on the electron-deficient anthracene moiety. However, the HOMO distributions were completely different. The HOMOs of the PhAnPy, DPhAnPy and PIAnPy were mostly distributed over the anthracene unit with little extension on the adjacent benzene and imidazole units, suggesting that the excited states were LE-dominated HLCT state which could ensure high PLQY. In contrast, the HOMO of PyIAnTPh was mostly localized on the pyrenoimidazole unit with a certain contribution from the anthracene, which induced a major CT emission characteristic. Electroluminescence Properties In view of the above-mentioned remarkable properties, the application of these materials as active layers for non-doped blue and white OLEDs were fabricated with a simple configuration of indium tin oxide (ITO)/HATCN (6 nm)/TAPC (25 nm)/TCTA (15 nm)/ EML (20 nm)/TPBi (40 nm)/LiF (0.5 nm)/Al (100 nm). In these devices, ITO, HATCN (dipyrazino(2,3-f:2’,3’-h)- quinoxaline-2,3,6,7,10,11-hexacarbonitrile), TAPC (4,4ʹ-cyclohexylidenebis( N , N -bis(4-methylphenyl), TCTA (tris(4-carbazoyl-9-ylphenyl)amine), TPBi (2,2′2″-(1,3,5‐ benzinetriyl)tris(1‐phenyl‐1‐ H ‐benzimidazole), LiF (lithium fluoride), and Al (aluminum) served as anode, hole injection layer, hole-transporting layer, electron/exciton-blocking layer, electron-transporting layer, electron injection layer, and cathode, respectively. The chemical structures and energy level diagrams of the functional materials for OLEDs were depicted in Figure S15 (Supporting Information). The electroluminescent performances of the four non-doped devices were shown in Fig. 6 and the data were listed Table 2 . All of devices showed extremely low turn-on voltages (V on ) below 3 V, indicating the small carrier injection barrier in these devices. As expected, the non-doped OLEDs based on PhAnPy and DPhAnPy exhibited pure blue emissions peaking at 452 nm under the voltage of 5 V, with the corresponding CIE coordinates of (0.16, 0.14) and (0.17, 0.17), respectively. Their EL spectra were very stable over the entire drive-voltage range from 4 to 9 V ( Figure S16 , Supporting Information). Significantly, both the non-doped devices exhibited excellent EL performances with maximal current efficiency (CE max ) of 10.64 and 11.09 cd A -1 , maximal power efficiency (PE max ) of 8.89 and 8.73 lm W -1 , maximum EQE of 10.24% and 8.27% for PhAnPy and DPhAnPy, respectively. Meanwhile, they displayed negligible efficiency roll-offs and the EQEs still remained at the high level of 9.63% and 7.68% for PhAnPy and DPhAnPy, respectively, under the brightness of 1000 cd m -2 . Apparently, the outstanding EL performances are among the best results of the non-doped blue fluorescent OLEDs ( Table S1 , Supporting Information). Table 1 Key photophysical properties of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy. Emitter λ abs a) (nm) λ em b) (nm) PLQY c) (%) t d) (ns) ΔE ST e) Sol Film Sol Film Sol Film Sol Film (eV) PhAnPy 357, 377, 397 350, 381, 402 440 453 75 48 2.83 0.83 0.99 DPhAnPy 358, 377, 397 347, 382, 402 441 470 64 41 2.91 4.50 0.91 PIAnPy 360, 377, 397 348, 383, 402 441 466, 588 79 52 2.53 1.76, 5.04 0.95 PyIAnPy 355, 383, 397 350, 386, 401 444 467, 601 60 39 2.39 1.94, 5.69 0.93 a) UV-vis absorption peaks in THF solution (10 − 5 M) and vacuum-deposited neat films at room temperature; b) Emission peaks in THF solution (10 − 5 M) and vacuum-deposited neat films at room temperature; c) Absolute photoluminescence quantum efficiency of THF solution (10 − 5 M) and vacuum-deposited neat films evaluated using an integrating sphere; d) Fluorescence lifetimes measured in THF solution (10 − 5 M) and vacuum-deposited neat films; e) S 1 -T 1 energy gap measured in 10 − 5 M THF solution at 77 K. Table 2 Key performance parameters of the EL performances of OLEDs based on nondoped devices PhAnPy, DPhAnPy, PIAnPy and PyIAnPy. Emitters V on a) (V) L max b) (cd m -2 ) CE max c) (cd A -1 ) PE max d) (lm W -1 ) EQE e) (%) Roll-off f) (%) λ EL g) (nm) CIE h) (x, y) PhAnPy 2.9 23144 10.64 8.89 10.24/9.63 5.9 452 (0.16, 0.14) DPhAnPy 2.9 12879 11.09 8.73 8.27/7.68 7.1 452 (0.17, 0.17) PIAnPy 2.8 50448 15.52 10.98 10.14/9.80 3.3 460, 596 (0.35, 0.26) PyIAnPy 2.8 18471 15.95 9.70 8.83/7.89 10.6 464, 596 (0.40, 0.32) a) V on : turn-on voltage at a luminescence of 1 cd m − 2 ; b) L max : maximum luminance; c) CE max : maximum current efficiency; d) PE max : maximum power efficiency; e) EQE: maximum EQE and the EQE value at 1000 cd m − 2 ; f) Efficiency roll-off at 1000 cd m − 2 ; g) λ EL : emission peak of the EL spectrum; h) CIE: Commission International de l’E´clairage (CIE) coordinates. The most intriguing point of this work is the single-emissive-layer WOLEDs based on PIAnPy and PyIAnPy. PIAnPy and PyIAnPy were verified to produce white lights owing to two distinct emission bands, blue regions (monomer) centered at 460 and 464 nm, as well as intense yellow bands (excimer) with peak at 596 nm. As shown in Fig. 6 , the CIE values of PIAnPy (0.35, 0.26) and PyIAnPy (0.40, 0.32) were both located in the white region at operating voltage of 5 V, close to the pure white light CIE coordinates of (0.33, 0.33). Clearly, The EL maximum values of excimer emissions in PIAnPy and PyIAnPy followed the same trends as observed in the PL spectra in thin films ( Figure S17 , Supporting Information), indicating that the white emissions were totally derived from the independent emissive layers of PIAnPy and PyIAnPy. In order to further confirm the origin of the excimer formation in the two non-doped WOLEDs, electron-only device (EOD), hole-only device (HOD) and single-layer device (SLD) were fabricated with the structures of ITO/HATCN (6 nm)/PyIAnPy (20 nm)/TPBi (40 nm)/LiF (0.5 nm)/Al (100 nm), ITO/HATCN (6 nm)/TAPC (25 nm)/TCTA (15 nm)/PyIAnPy (20 nm)/Al (100 nm) and ITO/HATCN (6 nm)/PyIAnPy (20 nm)/LiF (0.5 nm)/Al (100 nm), respectively. As shown in Figure S18 (Supporting Information), the EOD, HOD and SLD were also verified to produce white emission with two distinct emission bands around 464 and 596 nm in the blue and orange zone, which was unambiguously assigned to the excimer emission. In such approaches, the white spectra were successfully generated to cover the whole visible spectrum. The PIAnPy-based non-doped WOLED exhibited significantly higher EL performance than the PyIAnPy-based device owing to the enhanced LE excited-state component and higher PLQY in the film state. As depicted in Fig. 6 and Table 2 , the PIAnPy-based non-doped WOLED displayed a maximum luminance (L max ) of 50448 cd m -2 , an EQE max of 10.14%, a CE max of 15.52 cd A -1 and a PE max of 10.98 lm W -1 , relative to those of PyIAnPy-based non-doped WOLED (EQE max = 8.83%, L max = 18471 cd m -2 , CE max = 15.95 cd A -1 , and PE max = 9.70 lm W -1 ). Remarkably, the EQEs of non-doped PIAnPy and PyIAnPy devices still remained at high levels of 9.80% and 7.89% at the practical luminescence of 1000 cd m -2 , displaying extremely low efficiency roll-offs of 3.3% and 10.6%, respectively. To the best of our knowledge, these are the highest WOLED performance reported so far for single-component non-doped WOLEDs (Fig. 7 , detailed data were listed in Table S2 , Supporting Information). 12–14,18,19,23,25–31,42,43 Then, the exciton utilization efficiency ( η r ) of these emitters in device could be estimated by the following equation: $${\eta }_{EQE}=\gamma \times {\eta }_{PL}\times {\eta }_{r}\times {\eta }_{out}$$ where γ is the recombination efficiency of the injected carriers (ideally 100%); η PL is the PLQY of the neat films (48%, 41%, 52%, and 39% for PhAnPy, DPhAnPy, PIAnPy, and PyIAnPy, respectively); Assuming a light out-coupling efficiency ( η out ) of 30%, and the corresponding η r s of the PhAnPy, DPhAnPy, PIAnPy and PyIAnPy non-doped devices were calculated to be 71%, 67%, 65% and 75%, respectively, which was far superior the theoretical limit (25%) of conventional fluorescent OLEDs according to spin statistics, indicating certain triplet excitons were converted to singlet excitons through up conversion in the EL process. Considering the relatively short excited state lifetimes in the transient PL spectra and comparatively large energy gaps between S 1 and T 1 , the TADF process could not convert the triplet excitons into singlet excitons. The transient EL measurements at different driving voltages were shown in Figure S19 (Supporting Information). The EL intensity of these non-doped devices decreased rapidly due to the short fluorescence lifetime, and the delayed EL components were observed with obvious voltage dependence after the voltage pulse was turned off. The delay curves of the transient EL were fully fitted by the triplet-triplet annihilation (TTA) model rather than recombining the trapped charges. According to previous reports, 39 the proportion of delayed fluorescence caused by the TTA process were calculated to be 11.1%, 16.7%, 20.3% and 16.2% at 5 V for PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, respectively. Then, the singlet exciton that converted from the TTA process was 7.9% (71% × 11.1%), 11.2% (67% × 16.7%), 13.2% (65% × 20.3%) and 12.2% (75% × 16.2%), respectively, suggesting that TTA were not the dominant triplet exciton utilization mechanism for the high EUE, which was also supported by the good linear relationship in the brightness and current density curve of these four non-doped devices ( Figure S20 , Supporting Information). To further investigate the possible channel for harvesting energetic triplet excitons contributed to the high EUEs, TD-DFT calculations were adopted to analyze the energy levels of the excited states ( Figure S21 , Supporting Information). Considering the large energy gaps of over 0.8 eV between T 1 and high-lying triplet (T 2 /T 3 ) states and small energy level splits between the S 1 and T 3 states, the efficient hot exciton channel could be successfully activated, providing the prerequisite for high-lying RISC (hRISC) process from T 3 to S 1 . The spin-orbit coupling (SOC) values for all compounds were further calculated using the ORCA program. The SOC matrix element values between high-lying T 3 and S 1 (〈S 1 ĤSOT 3 〉) were also larger than that of the T 1 and S 1 (〈S 1 ĤSOT 1 〉). Meanwhile, the natural transition orbital (NTO) distributions of S 1 and T 3 were particularly similar ( Figure S22 , Supporting Information), possessing the different degree of mixed CT and LE (HLCT) excited-state characters, in which the faint CT component could further activate the hot exciton channel for RISC process. Owing to the short lifetime of hot exciton materials, the triplet involved annihilation processes would be effectively suppressed. Therefore, all these non-doped devices exhibited small efficiency roll-offs of less than 10% at practical brightness of 1000 cd m -2 . It is the first example of the efficient hot exciton channel-dominated single-component WOLED. Discussion In summary, four hot exciton materials, PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, are designed and successfully synthesized. All of them show high PLQYs and good thermal stability suitable for vacuum-deposited non-doped OLEDs. PhAnPy and DPhAnPy displayed highly efficient blue emission in neat films, while PIAnPy and PyIAnPy exhibit two sharp intense emission peaks at blue and yellow region. The emissions in the yellow zone in the neat films of PIAnPy and PyIAnPy are reasonably ascribed to the excimer emission as revealed by the X-ray analyses, transient lifetime measurement and concentration-dependent photophysical studies. The theoretical and experimental investigations also illustrate the HLCT characteristic of PIAnPy and PyIAnPy, which offers the possibility to harvest triplet excitons through the hot exciton channel and convert into singlet excitons. The non-doped OLEDs based on PhAnPy and DPhAnPy exhibit excellent blue EL performance with EQE max of 10.24% and 8.27% for PhAnPy and DPhAnPy, respectively. PyIAnPy displays a strong white-light emission with CIE coordinates of (0.40, 0.32), accompanied by the maximum EQE of 8.83%. More importantly, PIAnPy shows high potential in non-doped single-emissive-layer WOLED which exhibits an excellent EQE max of 10.14%, and extremely low-efficiency roll-off at high luminance (retain EQE = 9.8% at 1000 cd m -2 ) and CIE values of (0.35, 0.26), very close to pure white light. To the best of our knowledge, it is the first example that the efficient hot exciton channel-dominated WOLED based on single molecule is successfully fabricated. In particular, The EQE exceeds the theoretical limitation of conventional organic luminogens and the result represents the new efficiency record among single-component non-doped WOLEDs. This work not only comprehensively demonstrates the structure-property relationships of excimers, but also opens a new and facile strategy to fabricating excellent fluorescent WOLEDs based on single-component organic emitter through effective hot exciton molecular design. Materials and Methods All detailed experimental procedures for the synthesis and characterization, fabrication, and measurement of OLEDs, and characterization of this work are in the Supporting Information. Declarations Conflicts of interest There are no conflicts to declare. Author contributions F.L. performed the synthesis and characterization of the organic compound with the help of Z.F. H.L. and Z.C. performed the photophysical measurements and fabricated the OLEDs. T.L., H.L. and X.M. performed theoretical simulation of the molecules. P.L. devised the conceptual idea and supervised the experiments. All authors contributed to writing the manuscript. Acknowledgements This research is supported by the National Natural Science Foundation of China (22075100, 22375072), the Jilin Provincial Science and Technology Department (20220201082GX), Changchun Science and Technology Bureau (23JQ05) and the China Postdoctoral Science Foundation (2022TQ0111, 2023M731267). References Chen, Z., Ho, C.-L., Wang, L. & Wong, W.-Y. Single-Molecular White-Light Emitters and Their Potential WOLED Applications. Adv. Mater. 32, 1903269 (2020). Kido, J., Kimura, M. & Nagai, K. Multilayer White Light-Emitting Organic Electroluminescent Device. Science 267, 1332–1334 (1995). Reineke, S. et al. White Organic Light-Emitting Diodes with Fluorescent Tube Efficiency. Nature 459, 234–238 (2009). Xiang, H., Wang, R., Chen, J., Li, F. & Zeng, H. Research Progress of Full Electroluminescent White Light-Emitting Diodes based on a Single Emissive Layer. Light Sci. Appl. 10, 206 (2021). Sun, Y. et al. Management of Singlet and Triplet Excitons for Efficient White Organic Light-Emitting Devices. Nature 440, 908–912 (2006). Liu, H., Fu, Y., Tang, B. Z. & Zhao, Z. All-Fluorescence White Organic Light-Emitting Diodes with Record-Beating Power Efficiencies over 130 lm W -1 and small Roll-Offs. Nat. Commun. 13, 5154 (2022). Li, X.-L. et al. High-Efficiency WOLEDs with High Color-Rendering Index based on a Chromaticity-Adjustable Yellow Thermally Activated Delayed Fluorescence Emitter. Adv. Mater. 28, 4614–4619 (2016). Wang, R. et al. Highly Efficient Orange and White Organic Light-Emitting Diodes Based on New Orange Iridium Complexes. Adv. Mater. 23, 2823–2827 (2011). Zhang, Q.-W. et al. Multicolor Photoluminescence Including White-Light Emission by a Single Host-Guest Complex. J. Am. Chem. Soc. 138, 13541–13550 (2016). He, Z. et al. White Light Emission from a Single Organic Molecule with Dual Phosphorescence at Room Temperature. Nat. Commun. 8, 416 (2017). Gui, R. et al. Recent Advances in Dual-Emission Ratiometric Fluorescence Probes for Chemo/Biosensing and Bioimaging of Biomarkers. Chem. Rev. 383, 82–103 (2019). Chen, Y. H. et al. Insight Into the Mechanism and Outcoupling Enhancement of Excimer-Associated White Light Generation. Chem. Sci. 7, 3556–3563 (2016). Li, X. et al. Multiphotoluminescence from a Triphenylamine Derivative and Its Application in White Organic Light-Emitting Diodes Based on a Single Emissive Layer. Adv. Mater. 31, 1900613 (2019). Zhang, J. et al. AIEgen Configuration Transition and Aggregation Enable Dual Prompt Emission for Single-Component Nondoped White OLEDs. Aggregate, e410 (2023). Mazzeo, M. et al. Bright White Organic Light-Emitting Devices from a Single Active Molecular Material. Adv. Mater. 17, 34–39 (2005). Kasha, M. Characterization of Electronic Transitions in Complex Molecules. Discuss. Faraday Soc. 9, 14–19 (1950). Park, S. et al. A White-Light-Emitting Molecule: Frustrated Energy Transfer between Constituent Emitting Centers. J. Am. Chem. Soc. 131, 14043–14049 (2009). Tang, K.-C. et al. Fine Tuning the Energetics of Excited-State Intramolecular Proton Transfer (ESIPT): White Light Generation in A Single ESIPT System. J. Am. Chem. Soc. 133, 17738–17745 (2011). Zhang, Z. et al. Control of the Reversibility of Excited-State Intramolecular Proton Transfer (ESIPT) Reaction: Host-Polarity Tuning White Organic Light Emitting Diode on a New Thiazolo[5,4-d]thiazole ESIPT System. Chem. Mater. 28, 8815–8824 (2016). Jin, X.-H., Chen, C., Ren, C.-X., Cai, L.-X. & Zhang, J. Bright White-Light Emission from a Novel Donor-Acceptor Organic Molecule in the Solid State via Intermolecular Charge Transfer. Chem. Commun. 50, 15878–15881 (2014). Tu, D. et al. Highly Emissive Organic Single-Molecule White Emitters by Engineering o-Carborane-Based Luminophores. Angew. Chem. Int. Ed. 56, 11370–11374 (2017). Yang, Q.-Y. & Lehn, J.-M. Bright White-Light Emission from a Single Organic Compound in the Solid State. Angew. Chem. Int. Ed. 53, 4572–4577 (2014). Lee, J. et al. Excimer Formation in Organic Emitter Films Associated with a Molecular Orientation Promoted by Steric Hindrance. Chem. Commun. 50, 14145–14148 (2014). Wang, L. et al. Novel Host Materials for Single-Component White Organic Light-Emitting Diodes based on 9-Naphthylanthracene Derivatives. J. Mater. Chem. 18, 4529–4536 (2008). Fang, P. et al. Lanthanide Complexes with d-f Transition: New Emitters for Single-Emitting-Layer White Organic Light-Emitting Diodes. Light Sci. Appl. 12, 170 (2023). Chen, H. et al. Toward Achieving Single-Molecule White Electroluminescence from Dual Emission of Fluorescence and Phosphorescence. Chem. Mater. 32, 4038–4044 (2020). Wang, K. et al. Control of Dual Conformations: Developing Thermally Activated Delayed Fluorescence Emitters for Highly Efficient Single-Emitter White Organic Light-Emitting Diodes. ACS Appl. Mater. Interfaces 10, 31515–31525 (2018). Li, C. et al. An Organic Emitter Displaying Dual Emissions and Efficient Delayed Fluorescence White OLEDs. Adv. Opt. Mater. 7, 1801667 (2019). Li, B. et al. Realizing Efficient Single Organic Molecular White Light-Emitting Diodes from Conformational Isomerization of Quinazoline-Based Emitters. ACS Appl. Mater. Interfaces 12, 14233–14243 (2020). Tabata, K., Yamada, T., Kita, H. & Yamamoto, Y. Carbazole-Dibenzofuran Dyads as Metal-Free Single-Component White-Color Photoemitters. Adv. Funct. Mater. 29, 1805824 (2018). Chatsirisupachai, J. et al. Unique Dual Fluorescence Emission in the Solid State from a Small Molecule based on Phenanthrocarbazole with an AIE Luminogen as a Single-Molecule White-Light Emissive Material. Mater. Chem. Front. 5, 2361–2372 (2021). Gao, Z. et al. Highly Efficient Deep Blue Light Emitting Devices Based on Triphenylsilane Modified Phenanthro 9, 10-d Imidazole. Laser & Photon. Rev. 8, L6-L10 (2014). Liu, Y. et al. Highly Efficient Blue Organic Light-Emitting Diode Based on a Pyrene[4,5-d]Imidazole-Pyrene Molecule. CCS Chem. 4, 214–227 (2021). Liu, F. et al. Anthracene-Based Emitters for Highly Efficient Deep Blue Organic Light-Emitting Diodes with Narrow Emission Spectrum. Chem. Eng. J. 426, 131351 (2021). Liu, H. et al. One Stimulus In Situ Induces Two Sequential Luminescence Switchings in the Same Solvent-Fuming Process: Anthracene Excimer as the Intermediate. Adv. Funct. Mater. 29, 1901895 (2019). Liu, H. et al. Excimer-Induced High-Efficiency Fluorescence due to Pairwise Anthracene Stacking in a Crystal with Long Lifetime. Chem. Commun. 52, 7356–7359 (2016). Li, W. et al. A Twisting Donor-Acceptor Molecule with an Intercrossed Excited State for Highly Efficient, Deep-Blue Electroluminescence. Adv. Funct. Mater. 22, 2797–2803 (2012). Xu, Y. et al. Highly Efficient Blue Fluorescent OLEDs Based on Upper Level Triplet-Singlet Intersystem Crossing. Adv. Mater. 31, e1807388 (2019). Li, B. et al. “Exciton Recovery” Strategy in Hot Exciton Emitter toward High-Performance Non-Doped Deep-Blue and Host-Sensitized Organic Light-Emitting Diodes. Adv. Funct. Mater. 33, 2212876 (2023). Liu, F. et al. Triphenylene-Based Emitters with Hybridized Local and Charge-Transfer Characteristics for Efficient Nondoped Blue OLEDs with a Narrowband Emission and a Small Efficiency Roll-Off. ACS Appl. Mater. Interfaces 15, 47307–47316 (2023). Zhang, S. et al. Achieving a Significantly Increased Efficiency in Nondoped Pure Blue Fluorescent OLED: A Quasi-Equivalent Hybridized Excited State. Adv. Funct. Mater. 25, 1755–1762 (2015). Liu, D., Zhang, Z., Zhang, H. & Wang, Y. A Novel Approach Towards White Photoluminescence and Electroluminescence by Controlled Protonation of a Blue Fluorophore. Chem. Commun. 49, 10001 (2013). Reid, B. L. et al. Blue Emitting C2-symmetrical Dibenzothiazolyl Substituted Pyrrole, Furan and Thiophene. J. Mater. Chem. C 1, 2209 (2013). Scheme Scheme 1 is available in the Supplementary Files section. Additional Declarations (Not answered) Supplementary Files Onlinefloatimage2.png Scheme 1. Synthetic routes of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy. DPhAnPy.cif PIAnPy.cif PhAnPy.cif PyIAnPy.cif Supportinginformation.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4180968","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":285699352,"identity":"03ddba89-2aab-438c-863b-e8825b656f51","order_by":0,"name":"Ping lu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAApUlEQVRIiWNgGAWjYBACPgYGxgcSBSBmApFa2BgYmA0kDEjUwibBQJoWidxjFRYGhxn42XMMGH7uIEpLXtoNCaAWyZ43Boy9Z4jSkmMG1mJwI8eAmbGNSC0FIC32JGlhANsiQbQWnnfJEhIG6TwSZ54VHOwlRgs/e+7BzxIV1nL87ckbH/wkRgsDAw8DswSIBIIDRGkAKWb8QKTSUTAKRsEoGKEAAEeIKpMOwFJ8AAAAAElFTkSuQmCC","orcid":"","institution":"Jilin University","correspondingAuthor":true,"prefix":"","firstName":"Ping","middleName":"","lastName":"lu","suffix":""},{"id":285699353,"identity":"01587db4-dd32-4506-9b5d-c49c5dc7e276","order_by":1,"name":"Futong Liu","email":"","orcid":"","institution":"Jilin University","correspondingAuthor":false,"prefix":"","firstName":"Futong","middleName":"","lastName":"Liu","suffix":""},{"id":285699354,"identity":"a91556fc-c174-4033-a59e-fe0bc5848b0f","order_by":2,"name":"Hui Liu","email":"","orcid":"","institution":"Jilin University","correspondingAuthor":false,"prefix":"","firstName":"Hui","middleName":"","lastName":"Liu","suffix":""},{"id":285699355,"identity":"e2b7ee89-cd9d-4f1a-affd-ffd1b24ad118","order_by":3,"name":"Yichao Chen","email":"","orcid":"","institution":"South China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yichao","middleName":"","lastName":"Chen","suffix":""},{"id":285699356,"identity":"744e030f-97c1-44d4-9086-2209de1c8d36","order_by":4,"name":"Xin He","email":"","orcid":"","institution":"South China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Xin","middleName":"","lastName":"He","suffix":""},{"id":285699357,"identity":"26850383-4329-4402-8490-936b4de7ab1d","order_by":5,"name":"Zhuang Cheng","email":"","orcid":"","institution":"Jilin University","correspondingAuthor":false,"prefix":"","firstName":"Zhuang","middleName":"","lastName":"Cheng","suffix":""},{"id":285699358,"identity":"5b6bc36b-41ce-47c1-af17-90e231cea2de","order_by":6,"name":"Xiaobo Ma","email":"","orcid":"","institution":"Jilin University","correspondingAuthor":false,"prefix":"","firstName":"Xiaobo","middleName":"","lastName":"Ma","suffix":""},{"id":285699359,"identity":"04fa7ea5-dc1a-4109-9739-0a24e750c212","order_by":7,"name":"Xianfeng Qiao","email":"","orcid":"","institution":"South China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Xianfeng","middleName":"","lastName":"Qiao","suffix":""},{"id":285699360,"identity":"36d7c76d-c542-4e11-958e-be3e7bfb90f8","order_by":8,"name":"Dongge Ma","email":"","orcid":"","institution":"South China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Dongge","middleName":"","lastName":"Ma","suffix":""}],"badges":[],"createdAt":"2024-03-28 09:05:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4180968/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4180968/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54183455,"identity":"bed82fa4-894f-4608-bc15-848250f5743b","added_by":"auto","created_at":"2024-04-05 17:02:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":36089,"visible":true,"origin":"","legend":"\u003cp\u003eThe design strategy for single-molecule white emitters\u003c/p\u003e","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/1bd905b2fbf34aa72cf55fd7.png"},{"id":54183453,"identity":"c5d46199-c93d-43aa-b427-85e604b0a0cf","added_by":"auto","created_at":"2024-04-05 17:02:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":63846,"visible":true,"origin":"","legend":"\u003cp\u003eUV-vis and PL spectra of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy in dilute THF solution with concentration of 10\u003csup\u003e-5\u003c/sup\u003e M (a) and neat films (b); (c) the photoluminescence spectra of PyIAnPy neat film in vacuum and oxygen; (d) UV-vis and PL spectra of PyIAnPy in dilute THF solution recorded before and after deposition.\u003c/p\u003e","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/8fad1f5bdc323f2f7775d62c.png"},{"id":54183460,"identity":"a7fdd385-693e-46c3-890a-81b2beab51a2","added_by":"auto","created_at":"2024-04-05 17:02:18","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":70998,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Time-resolved emission decay curves obtained from the vacuum-deposited PyIAnPy neat film; (b) UV-vis absorption spectrum and excitation spectra of PyIAnPy neat film monitored at 470 nm and 600 nm; (c) The PL spectra of PyIAnPy in THF solutions with incremental concentrations from 1×10\u003csup\u003e-5\u003c/sup\u003e to 2×10\u003csup\u003e-2\u003c/sup\u003e M; (d) Temperature-dependent properties of PyIAnPy neat film.\u003c/p\u003e","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/8e84157127bd8cc5d4c21f62.png"},{"id":54183464,"identity":"43127967-8db1-42a8-b832-379b6699f900","added_by":"auto","created_at":"2024-04-05 17:02:18","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":119072,"visible":true,"origin":"","legend":"\u003cp\u003eThe single crystal structures and packing modes of (a) PhAnPy (CCDC 2323036), (b) DPhAnPy (CCDC 2323041), (c) PIAnPy, (CCDC 2323046) and (d) PyIAnPy (CCDC 2323050) in crystals.\u003c/p\u003e","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/cef2664547aa87d85ec5ed81.png"},{"id":54183466,"identity":"4eee390c-dd45-43fd-87e8-c0e95a6233b2","added_by":"auto","created_at":"2024-04-05 17:02:18","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":67525,"visible":true,"origin":"","legend":"\u003cp\u003eS\u003csub\u003e0\u003c/sub\u003e geometries and HOMO/LUMO distributions of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy.\u003c/p\u003e","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/3337a82276449bd0d8ddfba8.png"},{"id":54183465,"identity":"cf7feb3b-953c-4144-b471-92b5d92bd876","added_by":"auto","created_at":"2024-04-05 17:02:18","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":66714,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Current density-voltage-luminance (J-V-L) curves; (b) EQE-luminance characteristics (inset: EL spectra of the devices at 5 V); (c) Current efficiency-luminance-power efficiency curves; (d) The CIE coordinates diagram of nondoped devices PhAnPy, DPhAnPy, PIAnPy and PyIAnPy.\u003c/p\u003e","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/9c45cab3c1ec44c7422d3f9f.png"},{"id":54184164,"identity":"652222cb-53fa-4f13-988d-0fa526d57a9b","added_by":"auto","created_at":"2024-04-05 17:10:18","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":34478,"visible":true,"origin":"","legend":"\u003cp\u003eThe summary of the representative single-component WOLEDs, and the details of these devices are listed in \u003cstrong\u003eTable S2\u003c/strong\u003e (Supporting Information).\u003c/p\u003e","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/b8734da8b4a9e715c3e44811.png"},{"id":55411708,"identity":"38f78a64-29b5-4c2b-b26d-bb44b19fb208","added_by":"auto","created_at":"2024-04-27 01:33:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2309026,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/6023e07e-708e-4742-8ec6-2cdd611c4b82.pdf"},{"id":54183458,"identity":"a504ac6d-a67e-4821-9b4a-6dfef91c0e4c","added_by":"auto","created_at":"2024-04-05 17:02:17","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":43516,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1\u003c/strong\u003e. Synthetic routes of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy.\u003c/p\u003e","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/8a858748ef5eee9c88ca47ab.png"},{"id":54183459,"identity":"dd0c2ab4-5132-4e1f-af25-8b4dc76e4a58","added_by":"auto","created_at":"2024-04-05 17:02:17","extension":"cif","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3122739,"visible":true,"origin":"","legend":"","description":"","filename":"DPhAnPy.cif","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/c7d2ce5a77e99442189418c1.cif"},{"id":54183457,"identity":"1eec4610-b267-4439-9a9a-3150f346aa42","added_by":"auto","created_at":"2024-04-05 17:02:17","extension":"cif","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":1177741,"visible":true,"origin":"","legend":"","description":"","filename":"PIAnPy.cif","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/97156c5ed43f2cf6bda1f04a.cif"},{"id":54184163,"identity":"b5cabd69-7c98-41a1-9f7b-51efd497c92c","added_by":"auto","created_at":"2024-04-05 17:10:17","extension":"cif","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":1294210,"visible":true,"origin":"","legend":"","description":"","filename":"PhAnPy.cif","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/f6fd550bd10bd8ebfdb34614.cif"},{"id":54183467,"identity":"14063654-fbc9-445c-9cf5-c385ef8cfa6f","added_by":"auto","created_at":"2024-04-05 17:02:19","extension":"cif","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":34428,"visible":true,"origin":"","legend":"","description":"","filename":"PyIAnPy.cif","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/f065738ca18f8014d5d68847.cif"},{"id":54183462,"identity":"e01d2f8c-1644-4842-9e35-49fd2e41af37","added_by":"auto","created_at":"2024-04-05 17:02:18","extension":"docx","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":8499141,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"Supportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4180968/v1/76d4479999b7c5fe65fa1b24.docx"}],"financialInterests":"(Not answered)","formattedTitle":"Achieving Record External Quantum Efficiency of 10.14% in Non-Doped Single-Emissive-Layer White Light-Emitting Diodes Utilizing Hot Exciton Mechanism","fulltext":[{"header":"Introduction","content":"\u003cp\u003eLighting currently constitutes 15\u0026ndash;28% of the electric power consumption in the world. With the initiatives to reduce illumination-related energy consumption and carbon emission, white organic light-emitting diodes (WOLEDs) have drawn great attentions as the desirable candidates to realize large-scale flat and curved panels in high-quality displays and energy-saving solid-state lightings.\u003csup\u003e1\u003c/sup\u003e They offer a range of attractive characteristics such as self-luminescence, free of blue light hazard, wide viewing angle, good flexibility and considerable power efficiency that rivals the performance of the point and line lighting source from fluorescent lamps and inorganic LEDs.\u003csup\u003e2\u0026ndash;4\u003c/sup\u003e In principle, the device needs to exhibit emission spectrum continuously covering the whole visible region ranging from 400 to 700 nm to achieve white light. For this purpose, the reported high-performance WOLEDs usually consist of three primary-color (RGB) emitters or two complementary (blue and orange) emitters. In most cases, complicated device configurations are adopted to stack multiple emitting layers or mix various color chromophores into one emitting layer. In addition, excitons ratios have to be precisely manipulated to be formed properly on different emitters, and one or more interlayers are required to balance carriers as well as confine excitons within respective monochromic layers.\u003csup\u003e5\u0026ndash;7\u003c/sup\u003e Albeit the success in improving the external quantum efficiencies (EQEs) and power efficiencies, such WOLEDs may suffer from several issues including complex fabrication procedure, inevitable phase separation, poor color reproducibility and variable CIE coordinates under different voltages. The noble-metal containing phosphorescent materials are often involved in the emissive doping system, which generally improve the device cost, give rise to environmental pollution, and impede the widespread commercialization of WOLEDs to a large degree.\u003csup\u003e8\u0026ndash;11\u003c/sup\u003e To overcome these problems, a promising alternative strategy is to construct single-emitting-layer WOLEDs based on purely fluorescent materials, which can provide many advantages such as easier fabrication process, lower cost, free of phase separation and stable emission color.\u003csup\u003e4,12\u0026ndash;15\u003c/sup\u003e Besides, the precise selection of complex host-guest system and fine-tuning the doping concentration which is essential in traditional WOLEDs will be unnecessary by using single molecule as the emissive layer, laying the foundation for the fabrication of simple and cost-effective non-doped WOLEDs.\u003c/p\u003e \u003cp\u003eFor the preparation of efficient materials suitable for the application in non-doped single-emitting-layer WOLEDs, the key point is delicate control of the molecular excited state. According to the Kasha\u0026rsquo;s rule, the fluorescent material radiates monochromatic light that originates from the lowest excited singlet level (S\u003csub\u003e1\u003c/sub\u003e).\u003csup\u003e16\u003c/sup\u003e This will lead to the limited spectral bandwidths in common fluorescent materials. Noticeably, there are a few reports about addressing this challenge during the past decades by adopting excited-state intramolecular proton transfer (ESIPT)\u003csup\u003e17\u0026ndash;19\u003c/sup\u003e, charge-transfer (CT)\u003csup\u003e20,21\u003c/sup\u003e, excimer\u003csup\u003e12,14,22\u0026ndash;24\u003c/sup\u003e, room-temperature phosphorescence (RTP)\u003csup\u003e10,25,26\u003c/sup\u003e, delayed fluorescence (DF)\u003csup\u003e13,27\u0026ndash;29\u003c/sup\u003e and other mechanisms\u003csup\u003e13\u003c/sup\u003e to endow the emitters with multiple excited state and accordingly enable white light emission. However, few of them can exhibit white electroluminescence (EL) under electrical excitation in OLEDs applications.\u003csup\u003e4,10\u003c/sup\u003e At present, only several non-doped WOLEDs have been reported to yield EQE of about 5%, approaching the limit of traditional fluorescent materials since only 25% singlet excitons are spin allowed.\u003csup\u003e12\u0026ndash;14,30,31\u003c/sup\u003e Thus, developing the non-doped single-emitting-layer WOLEDs with EQE breakthrough the limitation of spin statistics remains a highly challenging task.\u003c/p\u003e \u003cp\u003eIn this work, we prepare a series of fluorescent materials PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, which constitute of imidazole derivatives (benzimidazole, diphenylimidazole, phenanthroimidazole, pyrenoimidazole) and polycyclic aromatic hydrocarbons (PAH, anthracene and pyrene) showing multi-excited states (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These compounds are designed in consideration of the following points: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) Imidazole possesses a bipolar carrier transportation nature, and extending the structure of imidazole with rigid aromatic rings, such as benzene, diphenyl, phenanthrene and pyrene, could effectively enlarge the π-conjugation structure as well as molecular rigidity to exhibit intense blue emission in short wavelength region.\u003csup\u003e32\u0026ndash;34\u003c/sup\u003e (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) Combination of PAH-based moieties of anthracene and pyrene initiate the formation of excimers between the excited state monomer and the ground state monomer, leading to a red-shift in emission spectra in long wavelength region. Moreover, the largely extended π-conjugation planes are conducive to the generation of abundant supramolecular interactions, such as hydrogen bonding, C-H\u0026hellip;π and π\u0026hellip;π stacking, which might regulate the aggregation state of the compounds and realize broadened excimer/aggregation emission.\u003csup\u003e35,36\u003c/sup\u003e (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) In our prior studies, it is found that materials with hot exciton mechanism provide high potentials to simultaneously achieve high-efficiency and low efficiency roll-off in non-doped device through the reverse intersystem crossing (RISC) channel from high-lying triplet excited states (T\u003csub\u003en\u003c/sub\u003e, n\u0026thinsp;\u0026gt;\u0026thinsp;1) to the singlet excited states (S\u003csub\u003em\u003c/sub\u003e, m\u0026thinsp;\u0026ge;\u0026thinsp;1).\u003csup\u003e37\u0026ndash;39\u003c/sup\u003e Anthracene and pyrene with delicate alignment of energy levels would be beneficial to induce the high-lying RISC process, showing high potential to achieve EQE exceeding 5%.\u003csup\u003e40\u003c/sup\u003e As a result, owing to the various energy alignments in short wavelength and long wavelength zone, the individual emission from imidazole-based chromorphores and PAH-based excimers could be obtained at the same time in PIAnPy and PyIAnPy, which eventually bring about a continuous electroluminescent spectrum close to standard white light. The resultant non-doped device incorporating PIAnPy as the active emitter is successfully fabricated, exhibiting white light with the CIE coordinates of (0.35, 0.26), the luminance over 50000 cd m\u003csup\u003e-2\u003c/sup\u003e and the excellent EQE of 10.14%. Moreover, the device displays very low efficiency roll-off of 3.3% under the luminance of 1000 cd m\u003csup\u003e-2\u003c/sup\u003e, which is the best result among non-doped single-emitting-layer WOLEDs. Whereas with a more extended π conjugation, PyIAnPy presents a much stronger excimer emission. PyIAnPy-based non-doped WOLED exhibits a stable emission approaching warm white light with a CIE of (0.40, 0.32) and a high EQE of 8.83%, which is also pioneering among single-emitting-layer WOLEDs reported so far. It is the first example that the efficient non-doped WOLED via the hot exciton mechanism can be fabricated. The state-of-the-art device performance demonstrates the great potential of this molecular design strategy in simultaneously achieving high efficiency and low efficiency roll-off for non-doped WOLED applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis and Characterization\u003c/h2\u003e \u003cp\u003eAs shown in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, PhAnPy, DPhAnPy, PIAnPy and PyIAnPy were all conveniently prepared by a two-step reaction. The brominated product of PyAnBr was first synthesized through the Suzuki coupling reaction between pyren-1-ylboronic acid and 9, 10-dibromoanthracene, which was further treated with intermediates PhPIB, DPhPIB, PPIB and PyPIB to afford PhAnPy, DPhAnPy, PIAnPy and PyIAnPy in high yields. All the target products were purified by column chromatography on silica gel and sublimated under vacuum condition. The molecular structures were fully characterized and verified by NMR and mass spectrometry. The synthetic details were provided in the Supporting Information. The thermal property of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy were examined. As shown in \u003cb\u003eFigure \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e\u003c/b\u003e (Supporting Information), PhAnPy, DPhAnPy, PIAnPy and PyIAnPy all exhibited high decomposition temperatures (\u003cem\u003eT\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e, corresponding to 5% weight loss) values of 473, 492, 500 and 505\u0026deg;C, respectively. The glass transition temperatures (\u003cem\u003eT\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e) of PhAnPy, DPhAnPy and PIAnPy were recorded at 177, 192 and 160\u0026deg;C, respectively. Additionally, the high melting points (\u003cem\u003eT\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e) of 333 and 362\u0026deg;C for both PhAnPy and DPhAnPy were observed. PyIAnPy showed no obvious exothermic or endothermic signals in the measurement cycle suggesting its high rigidity. Such high and tolerable temperatures indicated that they could retain amorphous morphology during vacuum thermal deposition process which was suitable for fabricating OLEDs by vacuum deposition technology. The cyclic voltammetry (CV) measurements were employed to investigate the electrochemical properties and estimate the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels of the emitters. As shown in \u003cb\u003eFigure S6\u003c/b\u003e, the HOMO/LUMO levels of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy were estimated to be -5.73/-2.97, -5.67/-2.89, -5.62/-2.84, and \u0026minus;\u0026thinsp;5.63/-2.86 eV, respectively, from the onset of the oxidation and reduction potential against the ferrocenium/ferrocene (Fc\u003csup\u003e+\u003c/sup\u003e/Fc) redox couple.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePhotophysical Properties\u003c/h3\u003e\n\u003cp\u003eThe UV-vis absorption and PL spectra in THF solution with a concentration of 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M were explored. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, PhAnPy, DPhAnPy, PIAnPy and PyIAnPy displayed the similar absorption profiles dominated by multiple localized π-π* transitions originating from the combination of imidazole, anthracene and pyrene segments. The absorption peaks with fine vibronic structures at 350\u0026ndash;400 nm were ascribed to the π-π* transitions of the core anthracene, while the higher-energy absorption bands at around 290\u0026ndash;350 nm were assigned to π-π* transition from the pyrene moiety. Their optical bandgaps (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e) were calculated to be around 2.76 eV\u0026ndash;2.78 eV. Under the excitation of a UV lamp, the compounds displayed very identical structureless emission with the maximum emission peaks in the range of 440\u0026ndash;444 nm. They also showed high PLQYs of 60\u0026ndash;79% measured by integrating sphere, and PIAnPy possessed the highest PLQY of 79% owing to the efficient radiative decay process. To deeply understand the properties of S\u003csub\u003e1\u003c/sub\u003e state, the solvation effects of these compounds were examined in various solvents. The PL spectra of PhAnPy, DPhAnPy and PIAnPy exhibited only tiny red-shifts of 12 nm, 12 nm and 13 nm as the solution polarity increased from hexane to acetonitrile, suggesting they possessed a locally emissive (LE) characteristic in the excited state (\u003cb\u003eFigure S8\u003c/b\u003e, Supporting Information). According to the Lippert-Mataga equation, the dipole moments were estimated to be 5.67 D, 6.55 D and 6.88 D for PhAnPy, DPhAnPy and PIAnPy, respectively, further implying that the LE characteristic was dominant in the S\u003csub\u003e1\u003c/sub\u003e state of these molecules (\u003cb\u003eFigure S9\u003c/b\u003e, Supporting Information). The situation was different in PyIAnPy. The emission peak of PyIAnPy showed a relatively larger red-shift of 26 nm demonstrating the stronger CT-state character from pyrenoimidazole to pyrene. PyIAnPy also displayed a typical two-section linear relationships in high- and low-polarity solvents, manifesting the LE-featured and CT-featured radiative transition, respectively. It was noteworthy that PyIAnPy exhibited single-exponential fluorescent decays in all the tested solvents (\u003cb\u003eFigure S10\u003c/b\u003e, Supporting Information), indicating the LE and CT components were well integrated into the hybridized local and charge transfer (HLCT) state rather than simply mixed state.\u003csup\u003e41\u003c/sup\u003e The fluorescent spectra were measured in THF solution at 77 K (\u003cb\u003eFigure S11\u003c/b\u003e, Supporting Information), and the corresponding energy levels of S\u003csub\u003e1\u003c/sub\u003e could be calculated to be 2.82, 2.74, 2.78 and 2.76 eV for PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, respectively. Nevertheless, no delayed emission spectra from phosphorescence were observed due to the low population and high non-radiative transition rate of T\u003csub\u003e1\u003c/sub\u003e state. To promote the production of the T\u003csub\u003e1\u003c/sub\u003e excitons, the classical PtOEP with a T\u003csub\u003e1\u003c/sub\u003e of 1.93 eV was adopted as a triplet sensitizer to populate the T\u003csub\u003e1\u003c/sub\u003e excitons through effective Dexter energy transfer (\u003cb\u003eFigure S11\u003c/b\u003e and \u003cb\u003eS12\u003c/b\u003e, Supporting Information).\u003csup\u003e38\u003c/sup\u003e The new emission peaks around 677 nm appeared in the 5 ms delayed phosphorescence spectrum when compared with that of the pristine PtOEP solution, thus the T\u003csub\u003e1\u003c/sub\u003e energy levels of these compounds were calculated to be around 1.83 eV. Based on these results, the TADF mechanism could further be excluded because of the large energy gaps of 0.91\u0026ndash;0.99 eV between S\u003csub\u003e1\u003c/sub\u003es and T\u003csub\u003e1\u003c/sub\u003es of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDifferent from the emission behavior in solution, all the compounds showed distinct emission spectra in the evaporated films (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb), PhAnPy and DPhAnPy exhibited bathochromic shift with the maximum emission peaks of 453 nm and 470 nm and large full-widths at half-maximum (FWHM) of 66 nm and 124 nm, respectively, due to the enhanced aggregation effect in the solid state. Particularly, PIAnPy exhibited bluish white light with the main emission peak at 466 nm and a weak emission band around 585 nm. PyIAnPy displayed a stronger white-light emission with two distinct peaks at 465 and 600 nm, which gave rise to a very broad emission band that covered the whole visible range extending from 400 to 750 nm. In order to eliminate phosphorescent interference, the PL spectra were further examined by altering the test condition from vacuum to oxygen. The similar results were obtained (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), indicating that the triplet exciton barely got involved in the PL behavior. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, the UV-Vis and PL spectra recorded before and after deposition were also consistent, implying that no chemical changes during vacuum deposition. To explore the origin of the white-light emission, time-resolved fluorescence of PyIAnPy in neat film state was measured (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). The lifetimes for PyIAnPy were 1.94 ns for peak at 465 nm and 5.69 ns for the peak at 600 nm. The largely red-shifted PL spectrum and longer-lived species that emitted at 600 nm from the PyIAnPy film were in good accordance with the characteristic of excimer according to the previous reports.\u003csup\u003e36\u003c/sup\u003e The excitation spectra of PyIAnPy monitored at either 465 nm or 600 nm were very similar and matched well with the absorption spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), which further confirmed that the excimer was originated from the common ground state and excluded the possibility of the formation of a new fluorophore. Accordingly, the assignment of this 600 nm peak in the PyIAnPy neat film to an excimer emission was reliable. Moreover, the PL spectra of PyIAnPy in THF solution at different concentrations were examined, and it was found that there was a new emission band appeared at the long wavelength of 580 nm upon the concentration of 0.01 M (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). As the temperature was increased from 296 K to 500 K, the fluorescence intensity was gradually enhanced along with the almost unchanged fluorescence maximum (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed), supporting the thermally activated excimer formation.\u003csup\u003e12\u003c/sup\u003e PIAnPy also showed an excimer emission at 585 nm, but its intensity was much weaker and narrower due to a different packing of the phenanthroimidazole moieties in PIAnPy compared to PyIAnPy which could not generate an intense white emission.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eCrystal Structures\u003c/h2\u003e \u003cp\u003eThe single crystals of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy were obtained via the temperature-gradient sublimation process. The PIAnPy and PyIAnPy crystals also exhibited dual emission with maximum peaks at 454 and 586 nm for PIAnPy, and 453 nm and 621 nm for PyIAnPy (\u003cb\u003eFigure S14\u003c/b\u003e, Supporting Information). X-ray structural analyses were further performed to resolve the molecular packing of above four crystals. As displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, PhAnPy, DPhAnPy, PIAnPy and PyIAnPy all adopted highly twisted molecular conformation, which could effectively suppress the intermolecular π-π stacking and ensure efficient radiative transition in solid state. In the PhAnPy crystal, two types of C-H\u0026hellip;π interactions were observed between the pyrene plane and H atom on the adjacent molecule with the distances of 2.663 and 2.739 \u0026Aring;. The C-H⋯π interactions with distances of 2.753\u0026ndash;2.763 \u0026Aring; and C-H⋯N (2.700 \u0026Aring;) hydrogen bonds were found in the crystals of DPhAnPy. Apparently, these weak intermolecular interactions contributed to stabilize the molecular structure, but the distances were not short enough in PhAnPy and DPhAnPy to generate the excimer emission. In contrast, the C-H\u0026middot;\u0026middot;\u0026middot;π interactions in PIAnPy were much stronger than those in PhAnPy and DPhAnPy with shorter distances of 2.501\u0026ndash;2.728 \u0026Aring; because of the more expanded π-conjugation. In particular, benefiting from the further extended pyrenoimidazole structure as well as the enhanced rigidity of the whole molecular plane, PyIAnPy possessed the most abundant and strongest C-H\u0026middot;\u0026middot;\u0026middot;π interactions with distances from 2.409 to 2.824 \u0026Aring; between one pyrenoimidazole, anthracene and pyrene planes as well as one edge-ring hydrogen atom from neighbouring molecule, demonstrating that a two-dimensional intermolecular network were formed by the edge-to-face interactions and close stacking mode in the crystal, which facilitated the formation of excimer in the aggregated state.\u003csup\u003e12\u003c/sup\u003e More importantly, the multiple hydrogen bonds could further stabilize the π-stacking interactions and lock the molecular rotations. Meanwhile, the absence of obvious π-π interaction is conducive to attain high PLQYs of 73%, 68%, 78% and 63% in PhAnPy, DPhAnPy, PIAnPy and PyIAnPy crystals, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eTheoretical calculations\u003c/h2\u003e \u003cp\u003eTo further investigate the relationship between molecular structures and electronic properties of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, the density functional theory (DFT) calculations were implemented. The optimized molecular structure and frontier molecular orbitals together with the corresponding calculated values were displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. PhAnPy, DPhAnPy, PIAnPy and PyIAnPy all revealed nearly orthogonal geometries between the anthracene and adjacent units of pyrene/imidazole derivatives with large dihedral angles of 79\u0026ndash;89\u0026deg;, which was well consistent with the single crystal structures. PhAnPy, DPhAnPy, PIAnPy and PyIAnPy had similar LUMO distributions, mainly localized on the electron-deficient anthracene moiety. However, the HOMO distributions were completely different. The HOMOs of the PhAnPy, DPhAnPy and PIAnPy were mostly distributed over the anthracene unit with little extension on the adjacent benzene and imidazole units, suggesting that the excited states were LE-dominated HLCT state which could ensure high PLQY. In contrast, the HOMO of PyIAnTPh was mostly localized on the pyrenoimidazole unit with a certain contribution from the anthracene, which induced a major CT emission characteristic.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eElectroluminescence Properties\u003c/h2\u003e \u003cp\u003eIn view of the above-mentioned remarkable properties, the application of these materials as active layers for non-doped blue and white OLEDs were fabricated with a simple configuration of indium tin oxide (ITO)/HATCN (6 nm)/TAPC (25 nm)/TCTA (15 nm)/ EML (20 nm)/TPBi (40 nm)/LiF (0.5 nm)/Al (100 nm). In these devices, ITO, HATCN (dipyrazino(2,3-f:2\u0026rsquo;,3\u0026rsquo;-h)- quinoxaline-2,3,6,7,10,11-hexacarbonitrile), TAPC (4,4ʹ-cyclohexylidenebis(\u003cem\u003eN\u003c/em\u003e,\u003cem\u003eN\u003c/em\u003e-bis(4-methylphenyl), TCTA (tris(4-carbazoyl-9-ylphenyl)amine), TPBi (2,2\u0026prime;2\u0026Prime;-(1,3,5‐ benzinetriyl)tris(1‐phenyl‐1‐\u003cem\u003eH\u003c/em\u003e‐benzimidazole), LiF (lithium fluoride), and Al (aluminum) served as anode, hole injection layer, hole-transporting layer, electron/exciton-blocking layer, electron-transporting layer, electron injection layer, and cathode, respectively. The chemical structures and energy level diagrams of the functional materials for OLEDs were depicted in \u003cb\u003eFigure S15\u003c/b\u003e (Supporting Information). The electroluminescent performances of the four non-doped devices were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and the data were listed Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. All of devices showed extremely low turn-on voltages (V\u003csub\u003eon\u003c/sub\u003e) below 3 V, indicating the small carrier injection barrier in these devices. As expected, the non-doped OLEDs based on PhAnPy and DPhAnPy exhibited pure blue emissions peaking at 452 nm under the voltage of 5 V, with the corresponding CIE coordinates of (0.16, 0.14) and (0.17, 0.17), respectively. Their EL spectra were very stable over the entire drive-voltage range from 4 to 9 V (\u003cb\u003eFigure S16\u003c/b\u003e, Supporting Information). Significantly, both the non-doped devices exhibited excellent EL performances with maximal current efficiency (CE\u003csub\u003emax\u003c/sub\u003e) of 10.64 and 11.09 cd A\u003csup\u003e-1\u003c/sup\u003e, maximal power efficiency (PE\u003csub\u003emax\u003c/sub\u003e) of 8.89 and 8.73 lm W\u003csup\u003e-1\u003c/sup\u003e, maximum EQE of 10.24% and 8.27% for PhAnPy and DPhAnPy, respectively. Meanwhile, they displayed negligible efficiency roll-offs and the EQEs still remained at the high level of 9.63% and 7.68% for PhAnPy and DPhAnPy, respectively, under the brightness of 1000 cd m\u003csup\u003e-2\u003c/sup\u003e. Apparently, the outstanding EL performances are among the best results of the non-doped blue fluorescent OLEDs (\u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e, Supporting Information).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eKey photophysical properties of PhAnPy, DPhAnPy, PIAnPy and PyIAnPy.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eEmitter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eλ\u003csub\u003eabs\u003c/sub\u003e\u003csup\u003ea)\u003c/sup\u003e (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eλ\u003csub\u003eem\u003c/sub\u003e\u003csup\u003eb)\u003c/sup\u003e (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003ePLQY\u003csup\u003ec)\u003c/sup\u003e (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003et\u003csup\u003ed)\u003c/sup\u003e (ns)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eΔE\u003csub\u003eST\u003c/sub\u003e\u003csup\u003ee)\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSol\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFilm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSol\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFilm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSol\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eFilm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSol\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eFilm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003e(eV)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhAnPy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e357, 377, 397\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e350, 381, 402\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e440\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e453\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDPhAnPy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e358, 377, 397\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e347, 382, 402\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e441\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e470\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.91\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePIAnPy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e360, 377, 397\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e348, 383, 402\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e441\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e466, 588\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1.76, 5.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePyIAnPy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e355, 383, 397\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e350, 386, 401\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e444\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e467, 601\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1.94, 5.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.93\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"10\"\u003e\u003csup\u003ea)\u003c/sup\u003eUV-vis absorption peaks in THF solution (10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M) and vacuum-deposited neat films at room temperature; \u003csup\u003eb)\u003c/sup\u003eEmission peaks in THF solution (10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M) and vacuum-deposited neat films at room temperature; \u003csup\u003ec)\u003c/sup\u003eAbsolute photoluminescence quantum efficiency of THF solution (10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M) and vacuum-deposited neat films evaluated using an integrating sphere; \u003csup\u003ed)\u003c/sup\u003eFluorescence lifetimes measured in THF solution (10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M) and vacuum-deposited neat films; \u003csup\u003ee)\u003c/sup\u003eS\u003csub\u003e1\u003c/sub\u003e-T\u003csub\u003e1\u003c/sub\u003e energy gap measured in 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M THF solution at 77 K.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eKey performance parameters of the EL performances of OLEDs based on nondoped devices PhAnPy, DPhAnPy, PIAnPy and PyIAnPy.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEmitters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003eon\u003c/sub\u003e\u003csup\u003ea)\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(V)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eL\u003csub\u003emax\u003c/sub\u003e\u003csup\u003eb)\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(cd m\u003csup\u003e-2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCE\u003csub\u003emax\u003c/sub\u003e\u003csup\u003ec)\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(cd A\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePE\u003csub\u003emax\u003c/sub\u003e\u003csup\u003ed)\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(lm W\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEQE\u003csup\u003ee)\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRoll-off\u003csup\u003ef)\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eλ\u003csub\u003eEL\u003c/sub\u003e\u003csup\u003eg)\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCIE\u003csup\u003eh)\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(x, y)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhAnPy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e23144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e10.24/9.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e5.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e452\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e(0.16, 0.14)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDPhAnPy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12879\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e8.27/7.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e7.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e452\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e(0.17, 0.17)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePIAnPy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50448\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e15.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e10.14/9.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e460, 596\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e(0.35, 0.26)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePyIAnPy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18471\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e15.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e8.83/7.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e464, 596\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e(0.40, 0.32)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003e\u003csup\u003ea)\u003c/sup\u003eV\u003csub\u003eon\u003c/sub\u003e: turn-on voltage at a luminescence of 1 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e; \u003csup\u003eb)\u003c/sup\u003eL\u003csub\u003emax\u003c/sub\u003e: maximum luminance; \u003csup\u003ec)\u003c/sup\u003eCE\u003csub\u003emax\u003c/sub\u003e: maximum current efficiency; \u003csup\u003ed)\u003c/sup\u003ePE\u003csub\u003emax\u003c/sub\u003e: maximum power efficiency; \u003csup\u003ee)\u003c/sup\u003eEQE: maximum EQE and the EQE value at 1000 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e; \u003csup\u003ef)\u003c/sup\u003eEfficiency roll-off at 1000 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e; \u003csup\u003eg)\u003c/sup\u003eλ\u003csub\u003eEL\u003c/sub\u003e: emission peak of the EL spectrum; \u003csup\u003eh)\u003c/sup\u003eCIE: Commission International de l\u0026rsquo;E\u0026acute;clairage (CIE) coordinates.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe most intriguing point of this work is the single-emissive-layer WOLEDs based on PIAnPy and PyIAnPy. PIAnPy and PyIAnPy were verified to produce white lights owing to two distinct emission bands, blue regions (monomer) centered at 460 and 464 nm, as well as intense yellow bands (excimer) with peak at 596 nm. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the CIE values of PIAnPy (0.35, 0.26) and PyIAnPy (0.40, 0.32) were both located in the white region at operating voltage of 5 V, close to the pure white light CIE coordinates of (0.33, 0.33). Clearly, The EL maximum values of excimer emissions in PIAnPy and PyIAnPy followed the same trends as observed in the PL spectra in thin films (\u003cb\u003eFigure S17\u003c/b\u003e, Supporting Information), indicating that the white emissions were totally derived from the independent emissive layers of PIAnPy and PyIAnPy. In order to further confirm the origin of the excimer formation in the two non-doped WOLEDs, electron-only device (EOD), hole-only device (HOD) and single-layer device (SLD) were fabricated with the structures of ITO/HATCN (6 nm)/PyIAnPy (20 nm)/TPBi (40 nm)/LiF (0.5 nm)/Al (100 nm), ITO/HATCN (6 nm)/TAPC (25 nm)/TCTA (15 nm)/PyIAnPy (20 nm)/Al (100 nm) and ITO/HATCN (6 nm)/PyIAnPy (20 nm)/LiF (0.5 nm)/Al (100 nm), respectively. As shown in \u003cb\u003eFigure S18\u003c/b\u003e (Supporting Information), the EOD, HOD and SLD were also verified to produce white emission with two distinct emission bands around 464 and 596 nm in the blue and orange zone, which was unambiguously assigned to the excimer emission. In such approaches, the white spectra were successfully generated to cover the whole visible spectrum. The PIAnPy-based non-doped WOLED exhibited significantly higher EL performance than the PyIAnPy-based device owing to the enhanced LE excited-state component and higher PLQY in the film state. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the PIAnPy-based non-doped WOLED displayed a maximum luminance (L\u003csub\u003emax\u003c/sub\u003e) of 50448 cd m\u003csup\u003e-2\u003c/sup\u003e, an EQE\u003csub\u003emax\u003c/sub\u003e of 10.14%, a CE\u003csub\u003emax\u003c/sub\u003e of 15.52 cd A\u003csup\u003e-1\u003c/sup\u003e and a PE\u003csub\u003emax\u003c/sub\u003e of 10.98 lm W\u003csup\u003e-1\u003c/sup\u003e, relative to those of PyIAnPy-based non-doped WOLED (EQE\u003csub\u003emax\u003c/sub\u003e = 8.83%, L\u003csub\u003emax\u003c/sub\u003e = 18471 cd m\u003csup\u003e-2\u003c/sup\u003e, CE\u003csub\u003emax\u003c/sub\u003e = 15.95 cd A\u003csup\u003e-1\u003c/sup\u003e, and PE\u003csub\u003emax\u003c/sub\u003e = 9.70 lm W\u003csup\u003e-1\u003c/sup\u003e). Remarkably, the EQEs of non-doped PIAnPy and PyIAnPy devices still remained at high levels of 9.80% and 7.89% at the practical luminescence of 1000 cd m\u003csup\u003e-2\u003c/sup\u003e, displaying extremely low efficiency roll-offs of 3.3% and 10.6%, respectively. To the best of our knowledge, these are the highest WOLED performance reported so far for single-component non-doped WOLEDs (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, detailed data were listed in \u003cb\u003eTable \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e\u003c/b\u003e, Supporting Information).\u003csup\u003e12\u0026ndash;14,18,19,23,25\u0026ndash;31,42,43\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThen, the exciton utilization efficiency (\u003cem\u003eη\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e) of these emitters in device could be estimated by the following equation:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$${\\eta }_{EQE}=\\gamma \\times {\\eta }_{PL}\\times {\\eta }_{r}\\times {\\eta }_{out}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eγ\u003c/em\u003e is the recombination efficiency of the injected carriers (ideally 100%); \u003cem\u003eη\u003c/em\u003e\u003csub\u003ePL\u003c/sub\u003e is the PLQY of the neat films (48%, 41%, 52%, and 39% for PhAnPy, DPhAnPy, PIAnPy, and PyIAnPy, respectively); Assuming a light out-coupling efficiency (\u003cem\u003eη\u003c/em\u003e\u003csub\u003eout\u003c/sub\u003e) of 30%, and the corresponding \u003cem\u003eη\u003c/em\u003e\u003csub\u003er\u003c/sub\u003es of the PhAnPy, DPhAnPy, PIAnPy and PyIAnPy non-doped devices were calculated to be 71%, 67%, 65% and 75%, respectively, which was far superior the theoretical limit (25%) of conventional fluorescent OLEDs according to spin statistics, indicating certain triplet excitons were converted to singlet excitons through up conversion in the EL process. Considering the relatively short excited state lifetimes in the transient PL spectra and comparatively large energy gaps between S\u003csub\u003e1\u003c/sub\u003e and T\u003csub\u003e1\u003c/sub\u003e, the TADF process could not convert the triplet excitons into singlet excitons. The transient EL measurements at different driving voltages were shown in \u003cb\u003eFigure S19\u003c/b\u003e (Supporting Information). The EL intensity of these non-doped devices decreased rapidly due to the short fluorescence lifetime, and the delayed EL components were observed with obvious voltage dependence after the voltage pulse was turned off. The delay curves of the transient EL were fully fitted by the triplet-triplet annihilation (TTA) model rather than recombining the trapped charges. According to previous reports,\u003csup\u003e39\u003c/sup\u003e the proportion of delayed fluorescence caused by the TTA process were calculated to be 11.1%, 16.7%, 20.3% and 16.2% at 5 V for PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, respectively. Then, the singlet exciton that converted from the TTA process was 7.9% (71% \u0026times; 11.1%), 11.2% (67% \u0026times; 16.7%), 13.2% (65% \u0026times; 20.3%) and 12.2% (75% \u0026times; 16.2%), respectively, suggesting that TTA were not the dominant triplet exciton utilization mechanism for the high EUE, which was also supported by the good linear relationship in the brightness and current density curve of these four non-doped devices (\u003cb\u003eFigure S20\u003c/b\u003e, Supporting Information). To further investigate the possible channel for harvesting energetic triplet excitons contributed to the high EUEs, TD-DFT calculations were adopted to analyze the energy levels of the excited states (\u003cb\u003eFigure S21\u003c/b\u003e, Supporting Information). Considering the large energy gaps of over 0.8 eV between T\u003csub\u003e1\u003c/sub\u003e and high-lying triplet (T\u003csub\u003e2\u003c/sub\u003e/T\u003csub\u003e3\u003c/sub\u003e) states and small energy level splits between the S\u003csub\u003e1\u003c/sub\u003e and T\u003csub\u003e3\u003c/sub\u003e states, the efficient hot exciton channel could be successfully activated, providing the prerequisite for high-lying RISC (hRISC) process from T\u003csub\u003e3\u003c/sub\u003e to S\u003csub\u003e1\u003c/sub\u003e. The spin-orbit coupling (SOC) values for all compounds were further calculated using the ORCA program. The SOC matrix element values between high-lying T\u003csub\u003e3\u003c/sub\u003e and S\u003csub\u003e1\u003c/sub\u003e (〈S\u003csub\u003e1\u003c/sub\u003eĤSOT\u003csub\u003e3\u003c/sub\u003e〉) were also larger than that of the T\u003csub\u003e1\u003c/sub\u003e and S\u003csub\u003e1\u003c/sub\u003e (〈S\u003csub\u003e1\u003c/sub\u003eĤSOT\u003csub\u003e1\u003c/sub\u003e〉). Meanwhile, the natural transition orbital (NTO) distributions of S\u003csub\u003e1\u003c/sub\u003e and T\u003csub\u003e3\u003c/sub\u003e were particularly similar (\u003cb\u003eFigure S22\u003c/b\u003e, Supporting Information), possessing the different degree of mixed CT and LE (HLCT) excited-state characters, in which the faint CT component could further activate the hot exciton channel for RISC process. Owing to the short lifetime of hot exciton materials, the triplet involved annihilation processes would be effectively suppressed. Therefore, all these non-doped devices exhibited small efficiency roll-offs of less than 10% at practical brightness of 1000 cd m\u003csup\u003e-2\u003c/sup\u003e. It is the first example of the efficient hot exciton channel-dominated single-component WOLED.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, four hot exciton materials, PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, are designed and successfully synthesized. All of them show high PLQYs and good thermal stability suitable for vacuum-deposited non-doped OLEDs. PhAnPy and DPhAnPy displayed highly efficient blue emission in neat films, while PIAnPy and PyIAnPy exhibit two sharp intense emission peaks at blue and yellow region. The emissions in the yellow zone in the neat films of PIAnPy and PyIAnPy are reasonably ascribed to the excimer emission as revealed by the X-ray analyses, transient lifetime measurement and concentration-dependent photophysical studies. The theoretical and experimental investigations also illustrate the HLCT characteristic of PIAnPy and PyIAnPy, which offers the possibility to harvest triplet excitons through the hot exciton channel and convert into singlet excitons. The non-doped OLEDs based on PhAnPy and DPhAnPy exhibit excellent blue EL performance with EQE\u003csub\u003emax\u003c/sub\u003e of 10.24% and 8.27% for PhAnPy and DPhAnPy, respectively. PyIAnPy displays a strong white-light emission with CIE coordinates of (0.40, 0.32), accompanied by the maximum EQE of 8.83%. More importantly, PIAnPy shows high potential in non-doped single-emissive-layer WOLED which exhibits an excellent EQE\u003csub\u003emax\u003c/sub\u003e of 10.14%, and extremely low-efficiency roll-off at high luminance (retain EQE\u0026thinsp;=\u0026thinsp;9.8% at 1000 cd m\u003csup\u003e-2\u003c/sup\u003e) and CIE values of (0.35, 0.26), very close to pure white light. To the best of our knowledge, it is the first example that the efficient hot exciton channel-dominated WOLED based on single molecule is successfully fabricated. In particular, The EQE exceeds the theoretical limitation of conventional organic luminogens and the result represents the new efficiency record among single-component non-doped WOLEDs. This work not only comprehensively demonstrates the structure-property relationships of excimers, but also opens a new and facile strategy to fabricating excellent fluorescent WOLEDs based on single-component organic emitter through effective hot exciton molecular design.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eAll detailed experimental procedures for the synthesis and characterization, fabrication, and measurement of OLEDs, and characterization of this work are in the Supporting Information.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflicts of interest\u003c/h2\u003e \u003cp\u003eThere are no conflicts to declare.\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eF.L. performed the synthesis and characterization of the organic compound with the help of Z.F. H.L. and Z.C. performed the photophysical measurements and fabricated the OLEDs. T.L., H.L. and X.M. performed theoretical simulation of the molecules. P.L. devised the conceptual idea and supervised the experiments. All authors contributed to writing the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis research is supported by the National Natural Science Foundation of China (22075100, 22375072), the Jilin Provincial Science and Technology Department (20220201082GX), Changchun Science and Technology Bureau (23JQ05) and the China Postdoctoral Science Foundation (2022TQ0111, 2023M731267).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChen, Z., Ho, C.-L., Wang, L. \u0026amp; Wong, W.-Y. Single-Molecular White-Light Emitters and Their Potential WOLED Applications. Adv. Mater. 32, 1903269 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKido, J., Kimura, M. \u0026amp; Nagai, K. Multilayer White Light-Emitting Organic Electroluminescent Device. Science 267, 1332\u0026ndash;1334 (1995).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReineke, S. et al. White Organic Light-Emitting Diodes with Fluorescent Tube Efficiency. Nature 459, 234\u0026ndash;238 (2009).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXiang, H., Wang, R., Chen, J., Li, F. \u0026amp; Zeng, H. Research Progress of Full Electroluminescent White Light-Emitting Diodes based on a Single Emissive Layer. Light Sci. Appl. 10, 206 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun, Y. et al. Management of Singlet and Triplet Excitons for Efficient White Organic Light-Emitting Devices. Nature 440, 908\u0026ndash;912 (2006).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, H., Fu, Y., Tang, B. Z. \u0026amp; Zhao, Z. All-Fluorescence White Organic Light-Emitting Diodes with Record-Beating Power Efficiencies over 130 lm W\u003csup\u003e-1\u003c/sup\u003e and small Roll-Offs. Nat. Commun. 13, 5154 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, X.-L. et al. High-Efficiency WOLEDs with High Color-Rendering Index based on a Chromaticity-Adjustable Yellow Thermally Activated Delayed Fluorescence Emitter. Adv. Mater. 28, 4614\u0026ndash;4619 (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, R. et al. Highly Efficient Orange and White Organic Light-Emitting Diodes Based on New Orange Iridium Complexes. Adv. Mater. 23, 2823\u0026ndash;2827 (2011).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, Q.-W. et al. Multicolor Photoluminescence Including White-Light Emission by a Single Host-Guest Complex. J. Am. Chem. Soc. 138, 13541\u0026ndash;13550 (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHe, Z. et al. White Light Emission from a Single Organic Molecule with Dual Phosphorescence at Room Temperature. Nat. Commun. 8, 416 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGui, R. et al. Recent Advances in Dual-Emission Ratiometric Fluorescence Probes for Chemo/Biosensing and Bioimaging of Biomarkers. Chem. Rev. 383, 82\u0026ndash;103 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, Y. H. et al. Insight Into the Mechanism and Outcoupling Enhancement of Excimer-Associated White Light Generation. Chem. Sci. 7, 3556\u0026ndash;3563 (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, X. et al. Multiphotoluminescence from a Triphenylamine Derivative and Its Application in White Organic Light-Emitting Diodes Based on a Single Emissive Layer. Adv. Mater. 31, 1900613 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, J. et al. AIEgen Configuration Transition and Aggregation Enable Dual Prompt Emission for Single-Component Nondoped White OLEDs. Aggregate, e410 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMazzeo, M. et al. Bright White Organic Light-Emitting Devices from a Single Active Molecular Material. Adv. Mater. 17, 34\u0026ndash;39 (2005).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKasha, M. Characterization of Electronic Transitions in Complex Molecules. Discuss. Faraday Soc. 9, 14\u0026ndash;19 (1950).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePark, S. et al. A White-Light-Emitting Molecule: Frustrated Energy Transfer between Constituent Emitting Centers. J. Am. Chem. Soc. 131, 14043\u0026ndash;14049 (2009).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTang, K.-C. et al. Fine Tuning the Energetics of Excited-State Intramolecular Proton Transfer (ESIPT): White Light Generation in A Single ESIPT System. J. Am. Chem. Soc. 133, 17738\u0026ndash;17745 (2011).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, Z. et al. Control of the Reversibility of Excited-State Intramolecular Proton Transfer (ESIPT) Reaction: Host-Polarity Tuning White Organic Light Emitting Diode on a New Thiazolo[5,4-d]thiazole ESIPT System. Chem. Mater. 28, 8815\u0026ndash;8824 (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJin, X.-H., Chen, C., Ren, C.-X., Cai, L.-X. \u0026amp; Zhang, J. Bright White-Light Emission from a Novel Donor-Acceptor Organic Molecule in the Solid State via Intermolecular Charge Transfer. Chem. Commun. 50, 15878\u0026ndash;15881 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTu, D. et al. Highly Emissive Organic Single-Molecule White Emitters by Engineering o-Carborane-Based Luminophores. Angew. Chem. Int. Ed. 56, 11370\u0026ndash;11374 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang, Q.-Y. \u0026amp; Lehn, J.-M. Bright White-Light Emission from a Single Organic Compound in the Solid State. Angew. Chem. Int. Ed. 53, 4572\u0026ndash;4577 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee, J. et al. Excimer Formation in Organic Emitter Films Associated with a Molecular Orientation Promoted by Steric Hindrance. Chem. Commun. 50, 14145\u0026ndash;14148 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, L. et al. Novel Host Materials for Single-Component White Organic Light-Emitting Diodes based on 9-Naphthylanthracene Derivatives. J. Mater. Chem. 18, 4529\u0026ndash;4536 (2008).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFang, P. \u003cem\u003eet al.\u003c/em\u003e Lanthanide Complexes with d-f Transition: New Emitters for Single-Emitting-Layer White Organic Light-Emitting Diodes. Light Sci. Appl. 12, 170 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, H. et al. Toward Achieving Single-Molecule White Electroluminescence from Dual Emission of Fluorescence and Phosphorescence. Chem. Mater. 32, 4038\u0026ndash;4044 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, K. et al. Control of Dual Conformations: Developing Thermally Activated Delayed Fluorescence Emitters for Highly Efficient Single-Emitter White Organic Light-Emitting Diodes. ACS Appl. Mater. Interfaces 10, 31515\u0026ndash;31525 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, C. et al. An Organic Emitter Displaying Dual Emissions and Efficient Delayed Fluorescence White OLEDs. Adv. Opt. Mater. 7, 1801667 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, B. et al. Realizing Efficient Single Organic Molecular White Light-Emitting Diodes from Conformational Isomerization of Quinazoline-Based Emitters. ACS Appl. Mater. Interfaces 12, 14233\u0026ndash;14243 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTabata, K., Yamada, T., Kita, H. \u0026amp; Yamamoto, Y. Carbazole-Dibenzofuran Dyads as Metal-Free Single-Component White-Color Photoemitters. Adv. Funct. Mater. 29, 1805824 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChatsirisupachai, J. et al. Unique Dual Fluorescence Emission in the Solid State from a Small Molecule based on Phenanthrocarbazole with an AIE Luminogen as a Single-Molecule White-Light Emissive Material. Mater. Chem. Front. 5, 2361\u0026ndash;2372 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao, Z. et al. Highly Efficient Deep Blue Light Emitting Devices Based on Triphenylsilane Modified Phenanthro 9, 10-d Imidazole. Laser \u0026amp; Photon. Rev. 8, L6-L10 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, Y. et al. Highly Efficient Blue Organic Light-Emitting Diode Based on a Pyrene[4,5-d]Imidazole-Pyrene Molecule. CCS Chem. 4, 214\u0026ndash;227 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, F. et al. Anthracene-Based Emitters for Highly Efficient Deep Blue Organic Light-Emitting Diodes with Narrow Emission Spectrum. Chem. Eng. J. 426, 131351 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, H. et al. One Stimulus In Situ Induces Two Sequential Luminescence Switchings in the Same Solvent-Fuming Process: Anthracene Excimer as the Intermediate. Adv. Funct. Mater. 29, 1901895 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, H. et al. Excimer-Induced High-Efficiency Fluorescence due to Pairwise Anthracene Stacking in a Crystal with Long Lifetime. Chem. Commun. 52, 7356\u0026ndash;7359 (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, W. et al. A Twisting Donor-Acceptor Molecule with an Intercrossed Excited State for Highly Efficient, Deep-Blue Electroluminescence. Adv. Funct. Mater. 22, 2797\u0026ndash;2803 (2012).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXu, Y. et al. Highly Efficient Blue Fluorescent OLEDs Based on Upper Level Triplet-Singlet Intersystem Crossing. Adv. Mater. 31, e1807388 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, B. et al. \u0026ldquo;Exciton Recovery\u0026rdquo; Strategy in Hot Exciton Emitter toward High-Performance Non-Doped Deep-Blue and Host-Sensitized Organic Light-Emitting Diodes. Adv. Funct. Mater. 33, 2212876 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, F. et al. Triphenylene-Based Emitters with Hybridized Local and Charge-Transfer Characteristics for Efficient Nondoped Blue OLEDs with a Narrowband Emission and a Small Efficiency Roll-Off. ACS Appl. Mater. Interfaces 15, 47307\u0026ndash;47316 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, S. et al. Achieving a Significantly Increased Efficiency in Nondoped Pure Blue Fluorescent OLED: A Quasi-Equivalent Hybridized Excited State. Adv. Funct. Mater. 25, 1755\u0026ndash;1762 (2015).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, D., Zhang, Z., Zhang, H. \u0026amp; Wang, Y. A Novel Approach Towards White Photoluminescence and Electroluminescence by Controlled Protonation of a Blue Fluorophore. Chem. Commun. 49, 10001 (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReid, B. L. et al. Blue Emitting C2-symmetrical Dibenzothiazolyl Substituted Pyrrole, Furan and Thiophene. J. Mater. Chem. C 1, 2209 (2013).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4180968/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4180968/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWhite organic light-emitting diodes (WOLEDs) based on non-doped single emitter can promise convenient fabrication technology, absent phase separation, minimal color-aging, and good reproducibility for next-generation displays and lightings. However, the pure organic materials that could radiate intense white light are extremely rare, and the external quamtum efficiencies (EQE) of previously reported non-doped white OLEDs do not exceed 5%. Hence, the straightforward preparation of single white light-emitting molecules for high-performance non-doped WOLEDs remains a high challenging task. Herein, we design and synthesize four hot exciton materials, PhAnPy, DPhAnPy, PIAnPy and PyIAnPy, which consist of anthracene, pyrene and imidazole functional groups. Based on the rational manipulation of intermolecular interaction and excited state property, PIAnPy and PyIAnPy display dual emission in the neat films originating from the monomer and excimer emission. Exploiting PIAnPy as a single emitter, a non-doped WOLED is fabricated with a record EQE of 10.14%, a maximum luminance exceeding 50000 cd m\u003csup\u003e-2\u003c/sup\u003e and the Commission Internationale de L'Eclairage coordinates of (0.35, 0.26). Its EQE maintains as high as 9.80% at the luminescence of 1000 cd m\u003csup\u003e-2\u003c/sup\u003e showing a very low efficiency roll-off. To the best of our knowledge, this is the best results of non-doped WOLEDs based on the single-component emitters reported to date.\u003c/p\u003e","manuscriptTitle":"Achieving Record External Quantum Efficiency of 10.14% in Non-Doped Single-Emissive-Layer White Light-Emitting Diodes Utilizing Hot Exciton Mechanism","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-05 17:02:12","doi":"10.21203/rs.3.rs-4180968/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e8907801-fddd-4b94-aec5-9c2e502cd372","owner":[],"postedDate":"April 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":30075501,"name":"Physical sciences/Optics and photonics/Lasers, LEDs and light sources/Organic LEDs"},{"id":30075502,"name":"Physical sciences/Physics/Electronics, photonics and device physics/Photonic devices"}],"tags":[],"updatedAt":"2024-04-27T01:25:14+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-05 17:02:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4180968","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4180968","identity":"rs-4180968","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}