Ultra-Narrowband Helical Emitter with Frontier Orbital Confinement for Stable Deep-Blue Hybrid-Tandem Organic Light-emitting Diodes

Ultra-Narrowband Helical Emitter with Frontier Orbital Confinement for Stable Deep-Blue Hybrid-Tandem Organic Light-emitting Diodes | 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 Ultra-Narrowband Helical Emitter with Frontier Orbital Confinement for Stable Deep-Blue Hybrid-Tandem Organic Light-emitting Diodes Lian Duan, Chuanqin Cheng, Minqiang Mai, Chenglong Li, Dongdong Zhang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7669597/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Mar, 2026 Read the published version in Nature Materials → Version 1 posted You are reading this latest preprint version Abstract Achieving efficient and stable deep-blue organic light-emitting diodes (OLEDs) with high color purity remains challenging, primarily due to the scarcity of blue emitters that simultaneously exhibit ultra-narrowband emission and high operational stability. Herein, we present a multiple-resonance emitter featuring a highly-twisted helical configuration with spatially-confined frontier molecular orbitals, thereby decoupling radiative transitions from structural distortion while mitigating spectral broadening from carbon–hydrogen bond repulsion and molecular aggregation. A sharp emission peaking at 460 nm with a full-width at half-maximum (FWHM) of only 12 nm is obtained in solution, which challenges the conventional belief that a twisted molecular skeleton compromises color purity. Remarkably, this emitter delivers cutting-edge performance with nearly identical spectra across emitting systems of varying polarity, enabling the realization of a unicolor hybrid-tandem OLED design that integrates complementary exciton-harvesting mechanisms to overcome the efficiency-lifetime trade-off inherent in conventional homogeneous tandem devices, while maintaining spectral uniformity. The targeted device concurrently achieves an external quantum efficiency of 39.7%, a lifetime of 539 hours to 90% of 1,000 cd·m⁻², a FWHM of 14 nm, and a chromaticity y-coordinate of 0.10. We further show that the stacking sequence of emitting units induces a twofold lifetime variation, which mainly arises from differences in outcoupling efficiency and photoelectric co-aging. This co-engineering strategy constitutes a substantial advance toward commercially viable ultrapure-blue OLED displays. Physical sciences/Materials science/Materials for optics/Lasers, LEDs and light sources/Organic LEDs Physical sciences/Chemistry/Materials chemistry/Optical materials Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Since the landmark demonstration of organic light-emitting diodes (OLEDs) in 1987, the field has been dedicated to developing stable devices capable of achieving unity internal quantum efficiency across the entire visible spectrum 1,2 . Despite substantial progress, realizing highly efficient and long‐lifetime deep‐blue OLEDs remains a formidable challenge 3,4 . Despite its multi-billion-dollar scale, the current OLED industry continues to rely on inefficient fluorescent emitters with triplet–triplet annihilation (TTA) for deep blue, which cannot utilize all excitons generated by electrical excitation 5,6 . Subsequent strategies, based on phosphorescent heavy‐metal complexes 7-9 and thermally activated delayed fluorescence (TADF) emitters 10-14 , have been developed to fully utilize excitons in electroluminescence. Notably, these materials can also serve as sensitizers for narrowband multiple‐resonance (MR) emitters, enhancing color purity and accelerating triplet consumption through fast Förster energy transfer 15-19 . Operational lifetime can be further improved by employing tandem architectures, wherein multiple discrete electroluminescent (EL) units are stacked in series 20,21 . This configuration significantly reduces the brightness requirements on each emitting unit, thereby extending device longevity. More recently, building upon their breakthrough in extending the lifetime of blue devices via the polariton-enhanced Purcell effect (PEP), Forrest et al. successfully applied this strategy to phosphorescent tandem OLEDs by double-sided PEP effect and achieved a tenfold improvement in operational lifetime, alongside superior color saturation 22,23 . Nevertheless, a critical trade-off remains: as color purity improves, operational lifetime declines drastically. Specifically, most devices with a CIEy coordinate ≤ 0.10 exhibit a lifetime of less than 20 hours—well below commercial requirements. A conventional strategy to attain deep blue emission involves blue-shifting the emission spectrum. However, research indicates that the correlation between emission energy and device stability follows Marcus theory rather than Arrhenius kinetics, implying that even a slight blue shift can significantly reduce operational lifetime 23-26 . Furthermore, such blue-shifted emitters impose more stringent requirements on the high energy gap of host materials. An alternative approach is to narrow the FWHM of the emitter to suppress the long-wavelength spectral tail, thereby increasing the average photon energy and enabling a bluer chromaticity coordinate 27 . Importantly, for a target chromaticity, an ultra-narrowband emitter allows for a moderately red-shifted emission peak, thereby stabilizing the emitter and relaxing the energy-level requirements on host and transporting materials. Considering that a monochromatic light at 467 nm can meet the color coordinate requirements of BT.2020, organic light-emitting materials with maximum emission wavelengths ( λ ₘₐₓ) below this value should be adopted to achieve deep blue emission 28 . On the other hand, for the development of displays that are physiologically friendly, it is essential to mitigate the potential "blue light hazard" and reduce the emission of blue light below 455 nm 29 . As a result, the spectral tuning window is subject to strict constraints: the λ ₘₐₓ should not exceed 467 nm, while the onset wavelength must stay above 455 nm. Previous attempts to narrow emission linewidths have mainly focused on extending the multiple-resonance frameworks via multi-boron-fused polycyclic aromatic hydrocarbons and the state-of-the-art quadruple-borylated emitter could realize a λ max of 458 nm with a FWHM of only 12 nm in solution 30 . Yet, most emitters struggle to meet the above constraints, and they also exhibit increased molecular weight and enhanced intermolecular interactions—both of which compromise thermal stability and device longevity. 30,31 . Although steric substitution or cyclic protective structures have been explored to suppress aggregation, few of them could result in adequate stability 32,33 . Therefore, achieving a balance between ultra narrowband emission, superior molecular stability, and deep-blue color remains a major challenge. To overcome these constraints, we departed from the conventional design of large planar MR frameworks and developed an advanced molecular architecture characterized by a highly twisted helical configuration with spatially confined frontier molecular orbitals. Challenging the conventional wisdom that twisted molecules inevitably impair color purity via structural distortion, our design strategically circumvents this limitation by precisely engineering orbital confinement to decouple radiative transitions from helical deformation while leveraging this framework to mitigate carbon-hydrogen (C–H) bond repulsion and suppress molecule aggregation. Benefiting from the weakened intermolecular interactions, this emitter successfully showed almost the same spectra in high polarity phosphor-sensitized fluorescence (PSF) and low polarity TTA systems, while also delivering high efficiency and prolonged operational lifetime in their respective configurations. This allows us to develop a novel unicolor hybrid-tandem architecture concept that synergistically integrates complementary exciton-utilization mechanisms: PSF unit for 100% internal quantum efficiency and TTA unit for enhanced operational lifetime. This innovative design overcomes the fundamental efficiency-lifetime trade-off inherent in conventional homogeneous tandem deep-blue OLEDs while maintaining perfect spectral uniformity. The proof-of-the-concept device achieved a high external quantum efficiency of 39.7%, an LT90 of 539 h at an L 0 of 1,000 cd m -2 , an ultra-narrow electroluminescence with FWHM of only 14 nm, and CIE coordinates of (0.13, 0.10). We further reveal that the stacking sequence of emitting units significantly influences operational lifetime—a two‐fold difference attributable to disparities in outcoupling efficiency and photoelectric co‐aging mechanisms. It is worth noting that our device performances even surpass recently reported state-of-the-art stable deep-blue phosphorescent tandem OLEDs in both device efficiency and stability with even bluer color 23 , representing the potential toward commercially viable ultrapure-blue OLEDs. Results Molecular design and theoretical calculation Fig. 1 illustrates the molecular design strategy proposed in this work. To gain deep insight into the relationship between molecular structure and photophysical properties, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were carried out at the B3LYP/6-31G (d, p) level. The selection of an appropriate parent molecule is crucial. Previous studies have shown that double-borylated π-skeletons with meta-substituted B–Ar–B fragments represent a highly promising approach for achieving narrow FWHM values of <20 nm, as exemplified by v -DABNA and BD-3Cz (also referred to as BBCZ-SB) 34,35 . Compared to v -DABNA, BD-3Cz exhibits a convergent structure and contains one fewer nitrogen atom in the fused core, resulting in a wider energy gap and a hypsochromic shift in emission. However, theoretical calculation indicates a high vibration intensity for BN-3Cz at frequency of 1573.6 cm⁻¹, leading to a relatively broad FWHM and a pronounced high-energy shoulder peak. This strong vibrational mode primarily stems from stretching vibrations of the 1- and 3-positioned carbazole units, driven by steric repulsion between adjacent C-H bonds-as indicated by large displacement vectors pushing these hydrogens away from each other. It is therefore envisioned that mitigating this repulsion could lead to a narrower emission spectrum and reduced shoulder intensity. In contrast to conventional approaches that extend planar multiple-resonance skeletons through additional boron incorporation, we proposed an innovative strategy employing a highly twisted helical configuration to eliminate C-H bond repulsion. As shown in Fig. 1a, we strategically replaced two carbazole units in BD-3Cz with 12H-benzofuro [3,2-a] carbazole (CzO) segments to create our target molecule BD-Cz-2CzO. The CzO group was specifically selected for its nonlinear architecture, which would restrict molecular extension to maintain deep-blue emission and provide unique reaction sites for helical structure formation. As detailed in the Supplementary Information, BD-Cz-2CzO was efficiently synthesized in three steps from commercially available precursors. The synthesis involved a classical directional nucleophilic substitution coupling followed by a high-yield "one-pot" lithiation-diboronation reaction. Comprehensive structural characterization was performed using nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. For comparative studies, we also synthesized BD-3Cz and BD-2Cz-CzO as reference compounds. The optimized molecule structures of those compounds in ground states (S 0 ) were shown in Supplementary Fig. 1, clearly demonstrating the successful formation of a helical configuration for BD-Cz-2CzO. Quantitative analysis revealed increasing molecular planarity parameters (MPP) of 1.12 Å, 1.37 Å, and 1.57 Å for BD-3Cz, BD-2Cz-CzO, and BD-Cz-2CzO, respectively (Supplementary Fig. 2). This progressive increase in MPP values confirms our design strategy of enhancing molecular twist through CzO group incorporation. The photophysical properties of all three compounds were measured in diluted toluene, and the collected results are presented in Fig.1b. Remarkably, BD-Cz-2CzO exhibits an ultra-narrowband deep-blue emission peak at 460 nm with a recorded FWHM of merely 12 nm (0.07 eV). To the best of our knowledge, this narrow FWHM is comparable to, or even surpasses, that of state-of-the-art quadruple-borylated deep-blue emitters-particularly when compared using eV as the unit of measurement (Supplementary Table 1). The other two references, however, showed relatively large FWHMs of 16 nm and 14 nm for BD-3Cz and BD-2Cz-CzO, respectively. Notably, as the number of CzO groups increases, not only is the FWHM narrowed, but the shoulder intensity also decreases-from 0.18 in BD-3Cz and 0.15 in BD-2Cz-CzO to 0.10 in BD-Cz-2CzO. Moreover, given its strong absorption band at 455 nm as illustrated in Supplementary Fig. 3, BD-Cz-2CzO displays an exceptionally small Stokes shift of only 5 nm, suggesting its minimal vibrational coupling between the S 0 and S 1 states and the minimal vibrational relaxation in the singlet excited state (S 1 ). Considering the large MPP value of BD-Cz-2CzO aforementioned, our findings reveal a deviation from conventional photophysical principles: while molecular twisting is typically associated with spectral broadening, BD-Cz-2CzO demonstrates an inverse relationship, exhibiting the most pronounced helical distortion yet the narrowest emission spectrum. This counterintuitive phenomenon is further corroborated by root mean square displacement (RMSD) analysis, which shows progressively increasing values from 0.053 (BD-3Cz) to 0.063 (BD-2Cz-CzO) to 0.073 (BD-Cz-2CzO) between S 0 and S 1 states. And as illustrated in Fig. 1c, the main structural deformation of BD-Cz-2CzO primarily localized at the benzofuran segment of the helical structure. These RMSD values quantitatively confirm the enhanced structural deformation upon excitation that accompanies the increased molecular twist. This apparent paradox between structural distortion and spectral narrowing highlights the unique photophysical behavior enabled by our helical molecular design. To elucidate the structure-property relationships of these three molecules, we conducted detailed theoretical calculations of their electronic properties. Fig.1d shows the electron density distributions of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), revealing that the HOMO is localized at ortho- and para-positions relative to the electron-donating nitrogen atoms, while the LUMO occupies meta-positions to nitrogen and ortho/para-positions to the electron-withdrawing boron atoms. These distributions exhibit characteristic hybrid π/non-bonding orbital features typical of MR emitters 36-38 . Hole-electron analysis using Multiwfn software 39,40 further demonstrated that the S 1 states of all three compounds exhibits partial intramolecular short-range charge-transfer (SRCT) characteristics (Supplementary Fig. 4), with large oscillator strengths ( f ) of 0.522, 0.427, and 0.305 for BD-3Cz, BD-2Cz-CzO, and BD-Cz-2CzO, respectively. A key distinction emerges in the frontier orbital distributions: unlike BD-3Cz where orbitals delocalize across the entire skeleton, BD-2Cz-CzO and BD-Cz-2CzO show negligible HOMO/LUMO density on the benzofuran moiety of CzO donors. Fragment analysis of CzO revealed that its HOMO primarily resides on the carbazole unit (82.17%, Supplementary Fig. 5), which can be attributed to two factors: first, carbazole's stronger electron-donating ability (electronegativity O (3.44)> N (3.04)> C (2.55)) results in a higher-lying HOMO; second, the oxygen atom's strategic connection to the void carbon atom minimizes orbital overlap between benzofuran and carbazole. This is further supported by the calculated HOMO energies: CzO (-5.44 eV) closely matches carbazole (-5.46 eV) and is significantly higher than benzofuran (-5.98 eV). In BD-Cz-2CzO, boron's strong electron-withdrawing nature further confines orbitals to carbazole segments, with benzofuran contributing minimally to both HOMO (4.74%) and LUMO (3.40%) distributions (Supplementary Fig. 6). Hole-electron analysis confirmed this localized character, showing the benzofuran segment contributes only 5.10 % to hole distribution and 2.54% to electron distribution during charge-transfer excitation (Supplementary Fig. 7). These results collectively demonstrate the effective orbital confinement in BD-Cz-2CzO, being away from the distortion-prone helical region. Therefore, though enlarging the geometric structural discrepancies between the S 0 and S 1 states, the distorted benzofuran-segment does not contribute to the radiative transition process and thus showed negligible influence on the spectra. Moreover, the limited orbital extension of the molecule also benefits to maintain blue emission without disturbing MR distributions. To further elucidate the origination of the smaller FWHM and the weaker shoulder of BD-Cz-2CzO, we calculated the reorganization energies ( λ ) of all three compounds using the Molecular Materials Property Prediction Package (MOMAP) 41,42 . Contrary to the RMSD results, we observed a progressive decrease in λ values from BD-3Cz to BD-2Cz-CzO to BD-Cz-2CzO (Fig.1e). This trend directly correlates with the narrowing of emission linewidths, as λ more accurately reflects the structural rearrangement during S 1 →S 0 transitions. Detailed vibrational mode analysis in Fig.1f revealed that the key differences emerge in the high-frequency region (>1000 cm⁻¹), which critically influences both spectral width and shoulder intensity. The introduction of CzO groups systematically reduces vibrational coupling in this region, particularly for modes associated with C-H wagging (1573.6 cm⁻¹ in BD-3Cz, λ =77.5 cm⁻¹). This reduction is most pronounced in BD-Cz-2CzO, where the helical structure completely eliminates steric repulsion between adjacent hydrogens, yielding a negligible λ of 2.6 cm⁻¹ at 1574.1 cm⁻¹. Complementary Huang-Rhys factor analysis (Fig. 1g) confirmed these findings, showing significantly reduced values in the high-frequency region for BD-Cz-2CzO compared to the reference compounds. These results demonstrate that our helical molecular design achieves ultra-narrow emission with suppressed shoulder through two key mechanisms: one is strategic localization of frontier orbitals away from distortion-prone regions to decouple radiative transitions from structural deformation, and another is effective mitigation of C-H repulsion through the twisted framework. This approach represents a significant departure from conventional planar designs, opening new possibilities for engineering high-performance narrowband emitters. Characterization and photophysical properties Single crystals of BD-2Cz-CzO and BD-Cz-2CzO were successfully grown through slow solvent evaporation in dichloromethane and characterized by single-crystal X-ray diffraction (Fig. 2a, 2b and Supplementary Tables 2-3). Structural analysis revealed fundamentally different packing behaviors between these two emitters. The BD-2Cz-CzO with only one-side twisting shows twist angles of 29.1° (CzO-benzene) and 20.9° (carbazole-benzene), and a 3.5 Å separation between benzofuran and carbazole units. Its crystal packing features both head-to-head and tail-to-tail arrangements with intermolecular distances of 3.4 Å and 3.5 Å, respectively. More significantly, the overlapping regions in this packing configuration coincide with areas of electronic transition, promoting intermolecular orbital interactions that can lead to spectral broadening and aggregation-caused quenching at elevated doping concentrations. On the contrary, the dual-side twisting BD-Cz-2CzO exhibits distinct structural parameters with dihedral angles of 34.2° and 34.1° between its CzO units and central benzene ring, with benzofuran segments separated by 3.6 Å. This molecule adopts a head-to-tail helical packing arrangement with an average intermolecular distance of 3.4 Å. Though the existence of π - π interactions, this molecule adopts a head-to-tail helical packing motif, with predominant intermolecular contacts occurring at the tail regions of the CzO units where electronic transitions are minimal. This packing mode effectively separates adjacent MR emitting-cores in spatial, benefiting the suppression of aggregation-induced spectral broadening and molecule stability issues. The striking contrast between these molecular architectures - the moderately twisted BD-2Cz-CzO versus the highly twisted helical BD-Cz-2CzO - provides clear evidence that the degree of molecular distortion plays a decisive role in determining anti-aggregation behavior. To evaluate the anti-aggregation capability of the helical structure, we examined doped films with varying concentrations (1-4 wt%) in SiCzCz: SiTrzCz2 (65: 35) host matrices. While BD-3Cz-doped films exhibited significant spectral broadening (FWHM up to 30 nm) and greatly enhanced shoulder intensity, and BD-2Cz-CzO showed moderate improvement, BD-Cz-2CzO maintained nearly identical deep-blue emission ( λ max of 466 nm, FWHM of 14 nm) across all doping concentrations (Fig. 2c-e). This exceptional spectral stability, accompanied by consistently high photoluminescence quantum yields (PLQYs) of >98%, directly demonstrates the superior anti-aggregation effect of the highly twisted helical architecture, which effectively increases intermolecular distances between emitting cores. Transient photoluminescence analysis of 2 wt% BD-Cz-2CzO doped films at room temperature revealed distinct decay components with a prompt lifetime of 9 ns and delayed lifetime of 52 μs. The remarkably high radiative decay rate ( k r ) of 8.4×10 7 s -1 should benefit from the efficient SRCT transition characteristic with large f value. Meanwhile, the moderate reverse intersystem crossing rate ( k RISC ) of 2.3×10 4 s -1 is consistent with the behavior observed in most multiple-resonance emitters (Supplementary Fig. 9 and Supplementary Table 4) 43 . This k RISC value directly correlates with the measured singlet-triplet energy gap (Δ E ST ) of 0.17 eV, as determined from low-temperature (77 K) fluorescence and phosphorescence spectra in Supplementary Fig. 10, which yielded singlet and triplet state energies of 2.77 eV and 2.60 eV, respectively. Besides, the helical molecular architecture favors excellent thermal stability. Thermogravimetric analysis (TGA) reveals a high decomposition temperature (T d ) of 523 °C at 5% weight loss (Supplementary Fig. 11), while the relatively low molecular weight (<900) ensures good vapor deposition processability. Crucially, the material maintains exceptional thermal stability during prolonged heating, as evidenced by high-performance liquid chromatography (HPLC) analysis showing >99.9% purity after 240 hours of continuous heating at 360°C (the operational evaporation temperature) (Supplementary Fig. 12). This combination of properties stands in stark contrast to conventional planar extended skeletons, which typically suffer from thermal degradation and compromised device longevity. Performance of single-unit OLEDs Owing to its excellent photophysical properties, BD-Cz-2CzO was further evaluated in single-unit devices based on TTA (S-TTA) and PSF (S-PSF) emitting mechanisms with device structures of ITO/ HATCN (5 nm)/ NPB (30 nm)/ BCzPh (10 nm)/ α,β-ADN: BD-Cz-2CzO (1-4 wt%, 30 nm)/ CzPhPy (10 nm)/ DPPyA: Liq (1:1, 30 nm)/ LiF (0.5 nm)/ Al (150 nm) and ITO/ HATCN (5 nm)/ NPB (30 nm)/ SiCzCz (10 nm)/ SiCzCz: SiTrzCz2: BD-02: BD-Cz-2CzO (65 wt%:35 wt%:10 wt%:1-4 wt%, 30 nm)/ SiTrzCz2 (10 nm)/ DPPyA: Liq (1:1, 30 nm)/ LiF (0.5 nm)/ Al (150 nm), respectively. The device structures and energy levels have been provided in Fig.3a and 3b. The blue phosphorescent material BD-02 in the emissive layer (EML) was utilized as a sensitizer due to its favorable PL spectral overlap with the absorption of the BD-Cz-2CzO (Supplementary Fig.13) 9 , ensuring sufficient energy transfer to maintain a narrowband spectral distribution and harvest triplet excitons to attain unit internal quantum efficiency (IQE). Both type devices showed sharp electroluminescence (EL) emission from the final emitter with λ max of 463 nm, FWHM of 13 nm and CIE y of 0.10 for S-TTA device while λ max of 464 nm, FWHM of 14 nm and CIE y of 0.11 for S-PSF device (Fig. 3c). It is interestingly to note that nearly identical EL spectra were observed for both devices. Typically, owing to the existence of solid-state solvation effect and uncomplete energy transfer, EL spectra of MR emitters would show relatively broader FWHM and redshifted λ max in the high polarity PSF device compared with the low polarity TTA system. The nearly identical EL spectra of both devices should arise from, on one hand, the twisted helical structure of our emitter, suppressing molecular interactions, and on the other hand, complete energy transfer owing to its extremely small stokes-shift and thus guarantee efficient sensitizer emission-emitter absorption overlap. This can be reflected by the fact that as the concentration of the emitter increased from 1 wt% to 4 wt%, all the devices achieved nearly identical deep-blue EL (Fig. 3c, and Supplementary Fig.14 and Supplementary Table 5). To the best of our knowledge, the observed extremely narrow EL spectra represents one of the narrowest emissions for MR emitters in OLEDs (Supplementary Table 1). Fig.3d showed the EQE-luminance characteristics and for S-TTA device, owing to the triplet recycle through TTA process, EQE max of 10.1% was obtained. While the optimal S-PSF device exhibited higher EQE max of 33.5% owing to its much higher internal quantum efficiency due to the sensitized process. Moreover, the high EQE also arises from the high horizontal emitting dipole orientation ( Θ //, max = 84%) of the emitter (Fig. 3e), which benefit light outcoupling. Excitingly, minimal efficiency roll-off was observed for S-PSF device with EQE of 27.9% at 1, 000 cd m -2 , which outperforms other deep-blue emitters with significant roll-offs at high luminance in the literature. A plausible reason for this is that the high k r of emitter could efficiently accelerate exciton radiative dynamics which avoiding exciton annihilations at high luminance. The stability of both devices was evaluated with a fixed current at an initial luminance (L 0 ) of 1, 000 cd m - ², revealing LT90 of 676 h and 150 h for S-TTA and S-PSF devices (Fig.3f). To the best of our knowledge, both devices show the cutting-edge efficiency and lifetime in their respective configurations at their specific colors 7 . The good stability could be attributed to the ultra-narrowband emission of the emitter to lower onset energy to reduce the proportion of high-energy photons of the emitter and mitigating the degradation probability of molecules in the excited state, ultimately leading to a longer lifetime. Moreover, the twisted structure of BD-Cz-2CzO enhance thermal stability and prevent the potential molecule interactions, and thus benefit operation stability. Previous works with extended MR skeletons would deteriorate molecule thermal stability and increase the chance for molecule interactions and thus poor stability. Performance of uni-color hybrid tandem OLED The nearly identical EL spectra and excellent performances of BD-Cz-2CzO in both S-PSF and S-TTA configurations enabled the development of the unicolor-hybrid-tandem (UHT) OLED concept, theoretically integrating complementary advantages of high efficiency from PSF unit and long lifetime from TTA unit. Fig.4a illustrated architectures of UHT devices and what deserves to mention is that two distinct configurations with inverted unit sequences can be fabricated: UHT-1 positions the PSF-unit closer to the light-emitting side, whereas UHT-2 adopts the opposite arrangement. Moreover, both device configurations employed an experimentally validated charge generation layer known for its stability and efficiency 44,45 . Fig.4b illustrates the identical sharp EL spectra of both devices with λ max at 464 nm, FWHMs of 14 nm and deep-blue CIE y coordinates of 0.10 and 0.11, respectively. This spectrum represents the narrowest one among reported deep-blue tandem OLEDs 15,23,30 . Moreover, this λ max is shorter than the theoretical 467 nm for BT.2020 blue and negligible emission below 455 nm owing to its smallest FWHM among reported deep-blue tandem devices, therefore potentially satisfying the constraint for physiologically friendly wide-color gamut displays. As shown in Supplementary Fig.15, the nearly identical current density-voltage characteristics observed in both devices indicates highly consistent charge transport properties across the two hybrid tandem architectures. This further suggests that the exciton recombination processes remain essentially equivalent between the two configurations, ultimately yielding matching internal quantum efficiencies (IQEs). The EQE-luminance characteristics in Fig.4c, however, revealed a slightly higher EQE max of 46.3% for UHT-1 while 39.7% for UHT-2, indicating distinct light outcoupling behaviors between the two architectures. Notably, both devices exhibited minimal efficiency roll-off, retaining EQEs of 42.4% and 37.2% at a practical luminance of 1,000 cd·m² for UHT-1 and UHT-2, respectively. The angular dependence of EL intensity was systematically investigated as documented in Supplementary Fig.16, which basically followed the Lambertian distribution, validating the high device efficiency. The operational stability of both devices was evaluated under constant current driving at an initial luminance of 1,000 cd/m². The measured LT90 values reached 263 hours for UHT-1 and 539 hours for UHT-2. To the best of our knowledge, the UHT-2 device represents a breakthrough with the longest LT90 reported so far to date for deep-blue OLED exceeding 20% EQE, not to mention its small CIE y of only 0.10 (Fig.4d, 4e, and Supplementary Table 6). The UHT devices demonstrate superior performance when compared with state-of-the-art homogeneous tandem phosphorescent OLEDs 23 . For comparative study, we fabricated two conventional tandem OLEDs: T-PSF (dual S-PSF units) and T-TTA (dual S-TTA units). As shown in Supplementary Fig.17 and Supplementary Table.7, these control devices exhibited the characteristic efficiency-stability trade-off: the T-PSF configuration achieved a higher EQE max of 67.7% but limited operational stability (LT90 of 228 h), whereas the T-TTA architecture showed superior lifetime (LT90 of 927 h) but significantly lower efficiency (EQE max of 21.8%). This marked contrast in performance metrics conclusively demonstrates the potential of the UHT concept in resolving the long-standing efficiency-stability compromise for deep-blue OLED applications. To investigate the underlying mechanism responsible for the substantial lifetime variation between the two hybrid tandem device configurations, we performed systematic optical simulations to analyze their respective optical modes as illustrated in Supplemntary Fig. 18. A distinct refractive index profiles between the two architectures was obtained, which could be attributed to the fact that while both configurations maintain identical charge transport layers, their EMLs and charge blocking layers exhibit markedly different refractive index, leading to variations in microcavity resonance characteristics and optical path lengths to the outcoupling substrate (Supplemntary Fig. 19). Specifically, in the UHT-1 configuration, the higher refractive index EML and blocking layers of the TTA-unit enhance interfacial reflections, consequently reducing the TTA-unit's emission contribution through intensified surface plasmon polariton (SPP) 46 , substrate and waveguide modes. Conversely, the PSF-units in this architecture benefit from their greater distance from the cathode, which substantially reduces SPP mode losses and thereby increases their relative contribution to total emission. The UHT-2 architecture demonstrates the opposite optical behavior. By positioning the TTA-unit away from the cathode, SPP mode losses are effectively minimized. Furthermore, the proximity to the anode, combined with favorable refractive index matching between the emitting/blocking layers and the transparent ITO substrate, significantly enhances light extraction efficiency. This optimized configuration allows the TTA-unit to contribute more substantially to the overall emission in UHT-2, while the PSF-unit in this architecture suffers from increased SPP losses and consequently reduced its emission contribution. To visualize this effect quantitatively, we introduced a parameter termed the relative light outcoupling efficiency (Fig.4f and 4g), denoted as η out, relative , defined as the ratio of the light outcoupling efficiency of the TTA-unit to that of the PSF-unit within the hybrid tandem device. This quantity is expressed as: where η out , TTA and η out , PSF represent the absolute outcoupling efficiencies of the TTA-unit and PSF-unit, respectively. Based on optical simulations, the calculated η out,relative was 0.78 for the UHT-1 device and 1.34 for UHT-2. These results indicate that the TTA-unit possesses higher contribution to the total emission in the UHT-2 architecture, which is inconsistent with the lower EQE but better operation stability of UHT-2 device, underscoring the pronounced influence of unit positioning on the overall emission balance in the hybrid tandem structure. Meanwhile, in tandem devices, due to the small stokes-shift of ultranarrowband emitter, there would generate self-absoprtion and thus photoelectric co-aging. And the different duration of TTA and PSF units would also induce different photoelectric co-aging discrepancy compared with the tandem devices with the same emitting-units. Here, the photoelectric tests of S-PSF and S-TTA devices with an initial luminance of 1000 cd m -2 under continuous light irradiation with a peak wavelength of 464 nm and a power density of approximately 1 mW cm -2 were conducted to further elucidate the issue of lifetime differences. As shown in Fig.4h , the luminance of S-PSF device significantly dropped to below 90% after 60 h, while the luminance of S-TTA device still maintained over 98% of the initial luminance in the same test duration. This notable performance disparity also led to the differences in the lifetime of hybrid tandem devices as the photoelectrically unstable PSF-unit contribute higher to the EL of UHT-1 device, resulting in the relatively shorter lifetime of UHT-1 device. Discussion In summary, contradicting conventional assumptions about twisted molecular skeletons compromising color purity, an innovative MR emitter featuring a highly-twisted helical molecular configuration with spatially-confined frontier molecular orbitals was developed for stable and ultra-narrowband emission. This unique design successfully decouples radiative transitions from structural distortions while effectively mitigating spectral broadening caused by both C-H bond repulsion and molecular aggregation, demonstrating exceptional photophysical characteristics with a proper λ max of 460 nm and a FWHM of 12 nm in solution. Remarkably, this emitter maintains nearly identical emission spectra in both PSF and TTA systems with cutting-edge performances. This enables the realization of unicolor hybrid-tandem OLED concept to integrates complementary exciton-harvesting mechanisms to simultaneously address the fundamental efficiency-lifetime trade-off while preserving spectral uniformity. The optimized device achieves outstanding performance metrics with an external quantum efficiency of 39.7%, a remarkable long LT90 of 539 hours at 1,000 cd·m⁻², an EL FWHM of 14 nm and CIE ­y of 0.10 concurrently. These findings may provide valuable insights for future development of high-performance deep-blue OLED materials and devices. Recently, LG Display announced a hybrid-tandem device incorporating a phosphorescent and a fluorescent unit, highlighting the growing commercial interest in this approach. (https://news.lgdisplay.com/en/2025/05/final-step-to-achieving-dream-oled-lg-display-becomesworlds-first-to-verify-commercialization-ofblue-phosphorescent-oled-panels/.) However, their design faces inherent challenges of spectral mismatch due to the different final emitters in each unit. Our architecture overcomes this limitation by employing the same final emitter in both units, thereby ensuring perfect spectral uniformity (i.e., unicolor emission) while preserving all performance advantages, representing a critical advancement in the pursuit of eventual commercialization. Declarations Data availability The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information file. The X-ray crystallographic coordinates for structures reported in this study have been deposited at the CCDC under deposition numbers 2484150 and 2484151. These data can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk/data_request/cif. Acknowledgements This work was supported by the National Key Basic Research and Development Program of China (Grant no. 2024YFB361210), the National Science Fund of China (Grant No. 22135004 and 52222308). Contributions L.D. and D.Z. supervised the project and conceived the conceptual idea and designed the experiments. C.C. synthesized and characterized the MR emitter. C. C., M.M., and C.L. performed the theoretical calculations, photophysical characterization, OLED fabrication, and measurement. D.Z. and L.D. analyzed the results and wrote the manuscript. References Tang, C. W. & VanSlyke, S. A. Organic electroluminescent diodes. Appl. Phys. Lett. 51 , 913-915 (1987). Hong, G. et al. A Brief History of OLEDs—Emitter Development and Industry Milestones. Adv. Mater. 33 , 2005630 (2021). Monkman, A. Why Do We Still Need a Stable Long Lifetime Deep Blue OLED Emitter? ACS Appl. Mater. Interfaces 14 , 20463-20467 (2022). Im, Y. et al. 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Highly Efficient Electroluminescent Materials with High Color Purity Based on Strong Acceptor Attachment onto B–N-Containing Multiple Resonance Frameworks. CCS Chem. 4 , 2065-2079 (2021). Wu, X., Ni, S., Wang, C.-H., Zhu, W. & Chou, P.-T. Comprehensive Review on the Structural Diversity and Versatility of Multi-Resonance Fluorescence Emitters: Advance, Challenges, and Prospects toward OLEDs. Chem. Rev. 125 , 6685-6752 (2025). Lu, T. A comprehensive electron wavefunction analysis toolbox for chemists, Multiwfn. The J. Chem. Phys. 161 , 082503 (2024). Lu, T. & Chen, F. Multiwfn: A multifunctional wavefunction analyzer. J. Comput. Chem. 33 , 580-592 (2012). Shuai, Z. Thermal Vibration Correlation Function Formalism for Molecular Excited State Decay Rates. Chin. J. Chem. 38 , 1223-1232 (2020). Shuai, Z. & Peng, Q. Organic light-emitting diodes: theoretical understanding of highly efficient materials and development of computational methodology. Nat. Sci. Rev. 4 , 224-239 (2017). Zhang, H. et al. Fast reverse intersystem crossing over 107 s−1 via near-enantiomeric charge-transfer transitions. Chem , 102685 (2025). Li, X. et al. High-Efficiency and Stable Tandem Organic Light-Emitting Diodes Based on In Situ Coordination-Activated N-Doping. Adv. Funct. Mater. 35 , 2500409 (2025). Liu, Z. et al. In situ-formed tetrahedrally coordinated double-helical metal complexes for improved coordination-activated n-doping. Nat. Commun. 13 , 1215 (2022). Fusella, M. A. et al. Plasmonic enhancement of stability and brightness in organic light-emitting devices. Nature 585 , 379-382 (2020). Methods General Information All starting materials and reaction solvent (ultra-dry) were obtained from commercial suppliers and were used without further purification. Further drying and distillation of commercially available ultra-dry solvents are required before use. The 1 H NMR and 13 C NMR spectra were obtained in deuterated solution utilizing a JEOL JNM-ECS400 NMR spectrometer. MALDI-TOF-MS data were performed on a Shimadzu AXIMA Performance MALDI-TOF instrument in positive detection modes. Thermogravimetric analysis (TGA) was conducted using a HITACHI STA200 instrument under a nitrogen atmosphere. Single-crystal X-ray diffraction data were recorded on a Bruker D8 Venture X-ray single-crystal diffractometer using Cu/Ga Kα radiation (λ = 1.54178/1.34139 Å) for the compound. The structure was solved using SHELXT and refined with SHELXL. All non-hydrogen atoms were refined anisotropically. The positions of hydrogen atoms were calculated and refined isotropically. UV-vis absorption spectra were recorded on a UV-2600 (Shimadzu) spectrophotometer. Photoluminescence (PL) spectra were acquired using a Hitachi F-7000 fluorescence spectrophotometer. The lifetimes of prompt fluorescence and delayed fluorescence were measured on an Edinburgh Fluorescence Spectroscopy FLS1000. Absolute PL quantum yields (PLQYs) were obtained with an absolute photoluminescence quantum yield measurement system Hamamatsu C9920-03G in an integrating sphere. Quantum Chemical Calculations All simulation calculations were conducted using the Gaussian 16 program package. The ground-state geometries were optimized via density functional theory (DFT) calculations in vacuum, employing the B3LYP hybrid functional and the 6-31G (d,p) basis set. Based on the optimized ground-state geometries, time-dependent DFT (TD-DFT) excited-state analyses were performed at the B3LYP/6-31G(d,p) level. Franck-Condon analyses of the emission spectra were performed according to the literature using the Gaussian 16 package 47 . The MPP values and RMSDs of the optimized structures at S 0 and S 1 states were analyzed by Visual Molecular Dynamics (VMD) software 48 . The Huang-Rhys (HR) factors and reorganization energies were calculated using the MOMAP software. Optical simulations were conducted using the methods in Supporting Information. Device Fabrication and Characterization All compounds underwent temperature gradient sublimation under high vacuum before use with a purity exceeding 99.9%. Organic light-emitting diodes (OLEDs) were fabricated on glass substrates coated with indium tin oxide (ITO), with multiple organic layers sandwiched between the transparent ITO anode at the bottom and the metal cathode at the top. Before device fabrication, the ITO glass substrates were carefully pre-cleaned. All material layers were deposited via vacuum evaporation in a vacuum chamber with a base pressure of 10 -5 torr. The deposition system allows the fabrication of the complete device structure in a single vacuum pumping cycle without breaking the vacuum. The deposition rate of organic layers was maintained at 0.5 ~ 1 Å/s. Doping was achieved through co-evaporation from separate evaporation sources with different evaporation rates. The current density, voltage, luminance, external quantum efficiency (EQE), electroluminescent spectra, and other characteristics were measured simultaneously using a Keithley 2400 source meter and an absolute EQE measurement system in an integrating sphere. The EQE measurement system is Hamamatsu C9920-12, equipped with a Hamamatsu PMA-12 Photonic Multichannel Analyzer C10027-02, which has a maximum detection wavelength of 1100 nm. References 47 Santoro, F., Lami, A., Improta, R., Bloino, J. & Barone, V. Effective method for the computation of optical spectra of large molecules at finite temperature including the Duschinsky and Herzberg–Teller effect: The Qx band of porphyrin as a case study. J. Chem. Phys. 128 , 224311 (2008). 48 Humphrey, W., Dalke, A. & Schulten, K. VMD: Visual molecular dynamics. J. Mol. Graphics 14 , 33-38 (1996). Tables Table1 | Summarized performance of OLEDs Devices λ EL a (nm) FWHM (nm) EQE b max/1000/5000 (%) PE c max/1000/5000 (lm W -1 ) CE d max/1000/5000 (cd A -1 ) CIE e ( x , y ) LT 90 f (h) S-PSF 464 14 33.5/27.9/22.5 33.2/18.4/10.4 31.7/25.8/20.6 (0.13,0.11) 150 S-TTA 463 13 10.1/9.4/8.5 8.9/5.4/3.5 8.7/8.0/7.2 (0.13,0.10) 676 UHT-1 464 14 46.3/42.4/36.4 22.8/15.2/10.0 42.4/37.8/31.9 (0.13,0.11) 263 UHT-2 464 14 39.7/37.2/33.6 20.8/14.4/10.1 40.1/36.7/32.6 (0.13,0.10) 539 BD-02 462 25 24.8/23.9/21.4 40.2/26.5/17.9 36.3/33.7/29.6 (0.16,0.19) 249 a EL peak wavelength. b Maximum external quantum efficiency (EQE) and EQE at 1000 and 5000 cd m -2 . c Maximum power efficiency (PE) and PE at 1000 and 5000 cd m -2 d Maximum current efficiency (CE) and CE at 1000 and 5000 cd m -2 . e CIE coordinates. f Recorded at an initial luminance of 1,000 cd m -2 . Additional Declarations There is NO Competing Interest. Supplementary Files SupportingInformationfinal.pdf Supplementary and Additional Information Cite Share Download PDF Status: Published Journal Publication published 27 Mar, 2026 Read the published version in Nature Materials → 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-7669597","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":523391833,"identity":"348dfea4-a323-40f0-b012-7fe8d732ecd2","order_by":0,"name":"Lian Duan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFklEQVRIiWNgGAWjYDCCA0D8oIKBgY0dxDMAIyBgI6Al4QxQDTMDYwPxWhLbgARYCwMRWvhuJD97kDhvmzwfMwP7wx8Fd+y2SyQ/YPhQdpiBf3YDVi2SN9LMDRK33TZsA9rSzGPwLHnnjDQDxhnnDjNI3DmAVYvBjQQzCaAWRrAWBoPDyUARA2betsMMBhIJOLSkf5NInHPbHqSl8QdYS/oH5r94teQAbWm4nQjS0sBjcNgOKGLAzIhHi+SZN2USCcduJ7cxMzbOBmpJMDjzpuBgz7l0Hokb2LXwHU/fJvGh5rbt/PbmAx9//Dlsb3A8feODH2XWcvwzsGtBApBoSQSRB4CYh5B6OLAnWuUoGAWjYBSMGAAAaYpja9d+UqcAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-2750-0972","institution":"Tsinghua University","correspondingAuthor":true,"prefix":"","firstName":"Lian","middleName":"","lastName":"Duan","suffix":""},{"id":523391834,"identity":"bb1dbde2-e7fa-402e-b489-5a11218caa2b","order_by":1,"name":"Chuanqin Cheng","email":"","orcid":"","institution":"Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Chuanqin","middleName":"","lastName":"Cheng","suffix":""},{"id":523391835,"identity":"fa817925-7097-46f7-9259-f5eeef7e0252","order_by":2,"name":"Minqiang Mai","email":"","orcid":"","institution":"Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Minqiang","middleName":"","lastName":"Mai","suffix":""},{"id":523391836,"identity":"b06ca902-9a1c-437f-9654-0b9da3e97674","order_by":3,"name":"Chenglong Li","email":"","orcid":"","institution":"Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Chenglong","middleName":"","lastName":"Li","suffix":""},{"id":523391837,"identity":"a0701aff-7d12-4988-bda0-fd29978b9d05","order_by":4,"name":"Dongdong Zhang","email":"","orcid":"https://orcid.org/0000-0002-8433-6200","institution":"Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Dongdong","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2025-09-22 06:30:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7669597/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7669597/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41563-026-02529-2","type":"published","date":"2026-03-27T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":92696034,"identity":"2c4f72b6-cb22-4301-ad5d-5d772d18fd22","added_by":"auto","created_at":"2025-10-03 07:05:01","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":506643,"visible":true,"origin":"","legend":"\u003cp\u003eMolecular design of BD-Cz-2CzO. a, The molecular structures and design strategies of BD-3Cz, BD-2Cz-CzO and BD-Cz-2CzO. b, Measured and calculated fluorescence spectra in dilute toluene at room temperature. Inset: the vibration modes corresponding to the marked frequencies in Fig. 1e. c, The root mean square displacement (RMSD) values of the optimized structures of BD-3Cz, BD-2Cz-CzO and BD-Cz-2CzO in their S\u003csub\u003e0\u003c/sub\u003e and S\u003csub\u003e1\u003c/sub\u003e states. d, HOMO and LUMO distributions of BD-3Cz, BD-2Cz-CzO and BD-Cz-2CzO. e, Schematic potential energy diagram of the S\u003csub\u003e0\u003c/sub\u003e and the S\u003csub\u003e1\u003c/sub\u003e related to the \u003cem\u003eλ\u003c/em\u003e. f, The relationship between reorganization energy\u003cem\u003e \u003c/em\u003eand frequency that describe the contributions of each vibrational mode to the reorganization energy\u003cem\u003e \u003c/em\u003efor the S\u003csub\u003e1\u003c/sub\u003e-S\u003csub\u003e0\u003c/sub\u003e transitions. g, The Huang–Rhys factors of BD-3Cz, BD-2Cz-CzO and BD-Cz-2CzO under different vibrational modes.\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7669597/v1/db94eb9022f96fc978efdd22.jpg"},{"id":92696032,"identity":"851cd16b-36de-437a-a558-5a990eb4ba96","added_by":"auto","created_at":"2025-10-03 07:05:01","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":60824,"visible":true,"origin":"","legend":"\u003cp\u003eSingle crystal structures and photophysical analysis. a-b, Single-crystal X-ray diffraction molecular structures of BD-2Cz-CzO (a) and BD-Cz-2CzO (b). c-e, PL spectra of BD-3Cz (c), BD-2Cz-CzO (d), and BD-Cz-2CzO (e) in solid film with a doping concentration of 1, 2 and 4 wt %, respectively.\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7669597/v1/da3e8ffdc2f311bde01aa46d.jpg"},{"id":92696035,"identity":"dbed14c2-15ad-4c6c-a274-fe73bc19c747","added_by":"auto","created_at":"2025-10-03 07:05:01","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":172768,"visible":true,"origin":"","legend":"\u003cp\u003eEL performance of single PSF device (S-PSF) and TTA device (S-TTA) based on BD-Cz-2CzO and device based on BD-02. a, Device architectures with energy-level alignment of the relevant materials. b, Chemical structures of the materials used in the devices. c, The EL spectra of S-PSF, S-TTA and BD-02 based OLED devices at luminance of 1,000 cd m\u003csup\u003e-2\u003c/sup\u003e. d, External quantum efficiency versus luminance versus luminance (EQE-L) curves of S-PSF, S-TTA and BD-02 based OLED devices. e, Angle-dependent PL spectra of 1%, 2%, and 4%wt BD-Cz-2CzO doped films. f, The operation lifetime of the devices at an initial luminance of 1,000 cd m\u003csup\u003e-2\u003c/sup\u003e. L, luminance of the device during the operational lifetime measurement; L\u003csub\u003e0\u003c/sub\u003e, initial luminance of the device.\u003c/p\u003e","description":"","filename":"Picture8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7669597/v1/fa5cb85b354e939c2399ca0b.jpg"},{"id":92697261,"identity":"fc6de64a-bf34-43fb-8bed-6fec8f0c8e18","added_by":"auto","created_at":"2025-10-03 07:13:01","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":126390,"visible":true,"origin":"","legend":"\u003cp\u003eEL performance of hybrid tandem device (UHT-1 and UHT-2). a, The device architectures of hybrid tandem OLED. b, The EL spectra of UHT-1 and UHT-2 based OLED devices at luminance of 1,000 cd m\u003csup\u003e-2\u003c/sup\u003e.c, EQE-L curves of UHT-1 and UHT-2 based OLED devices. d, The operation lifetimes of the devices at an initial luminance of 1,000 cd m\u003csup\u003e-2\u003c/sup\u003e. e, Performance of recently reported stable deep-blue (λ\u003csub\u003eEL\u003c/sub\u003e≤467 nm) bottom-emitting devices. f-g, Relative light outcoupling efficiency in UHT-1 (f) and UHT-2 (g) devices. The horizontal axis represents the results for different thicknesses of the electron transport layer. The vertical axis represents the relative light outcoupling efficiency, which is the ratio of the light outcoupling efficiency of the TTA-unit to that of the PSF-unit. h, The photoelectric tests results of S-PSF and S-TTA devices with an initial luminance of 1000 cd m\u003csup\u003e-2\u003c/sup\u003e under continuous light irradiation.\u003c/p\u003e","description":"","filename":"Picture9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7669597/v1/63d4e67eb15e852c8823b4a0.jpg"},{"id":105617768,"identity":"e4741e32-af2f-4a4a-b2dc-95f86a9a9abd","added_by":"auto","created_at":"2026-03-28 07:05:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1659213,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7669597/v1/09e394e2-406c-491a-9bac-c67e9f91ab5a.pdf"},{"id":92696037,"identity":"1b09659c-75ba-4652-901d-b602afe76565","added_by":"auto","created_at":"2025-10-03 07:05:01","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":2530636,"visible":true,"origin":"","legend":"Supplementary and Additional Information","description":"","filename":"SupportingInformationfinal.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7669597/v1/615f0fcdf7ab981cca085385.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Ultra-Narrowband Helical Emitter with Frontier Orbital Confinement for Stable Deep-Blue Hybrid-Tandem Organic Light-emitting Diodes","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSince the landmark demonstration of organic light-emitting diodes (OLEDs) in 1987, the field has been dedicated to developing stable devices capable of achieving unity internal quantum efficiency across the entire visible spectrum\u003csup\u003e1,2\u003c/sup\u003e. Despite substantial progress, realizing highly efficient and long‐lifetime deep‐blue OLEDs remains a formidable challenge\u003csup\u003e3,4\u003c/sup\u003e.\u0026nbsp;Despite its multi-billion-dollar scale, the current OLED industry continues to rely on inefficient fluorescent emitters with triplet\u0026ndash;triplet annihilation (TTA) for deep blue, which cannot utilize all excitons generated by electrical excitation\u003csup\u003e5,6\u003c/sup\u003e. Subsequent strategies, based on phosphorescent heavy‐metal complexes\u003csup\u003e7-9\u0026nbsp;\u003c/sup\u003eand thermally activated delayed fluorescence (TADF) emitters\u003csup\u003e10-14\u003c/sup\u003e, have been developed to fully utilize excitons in electroluminescence. Notably, these materials can also serve as sensitizers for narrowband multiple‐resonance (MR) emitters, enhancing color purity and accelerating triplet consumption through fast F\u0026ouml;rster energy transfer\u003csup\u003e15-19\u003c/sup\u003e. Operational lifetime can be further improved by employing tandem architectures, wherein multiple discrete electroluminescent (EL) units are stacked in series\u003csup\u003e20,21\u003c/sup\u003e. This configuration significantly reduces the brightness requirements on each emitting unit, thereby extending device longevity. More recently, building upon their breakthrough in extending the lifetime of blue devices via the polariton-enhanced Purcell effect (PEP), Forrest et al. successfully applied this strategy to phosphorescent tandem OLEDs by double-sided PEP effect and achieved a tenfold improvement in operational lifetime, alongside superior color saturation\u003csup\u003e22,23\u003c/sup\u003e. Nevertheless, a critical trade-off remains: as color purity improves, operational lifetime declines drastically. Specifically, most devices with a CIEy coordinate \u0026le; 0.10 exhibit a lifetime of less than 20 hours\u0026mdash;well below commercial requirements.\u003c/p\u003e\n\u003cp\u003eA conventional strategy to attain deep blue emission involves blue-shifting the emission spectrum. However, research indicates that the correlation between emission energy and device stability follows Marcus theory rather than Arrhenius kinetics, implying that even a slight blue shift can significantly reduce operational lifetime\u003csup\u003e23-26\u003c/sup\u003e. Furthermore, such blue-shifted emitters impose more stringent requirements on the high energy gap of host materials. An alternative approach is to narrow the FWHM of the emitter to suppress the long-wavelength spectral tail, thereby increasing the average photon energy and enabling a bluer chromaticity coordinate\u003csup\u003e27\u003c/sup\u003e. Importantly, for a target chromaticity, an ultra-narrowband emitter allows for a moderately red-shifted emission peak, thereby stabilizing the emitter and relaxing the energy-level requirements on host and transporting materials. Considering that a monochromatic light at 467 nm can meet the color coordinate requirements of BT.2020, organic light-emitting materials with maximum emission wavelengths (\u003cem\u003e\u0026lambda;\u003c/em\u003eₘₐₓ) below this value should be adopted to achieve deep blue emission\u003csup\u003e28\u003c/sup\u003e. On the other hand, for the development of displays that are physiologically friendly, it is essential to mitigate the potential \u0026quot;blue light hazard\u0026quot; and reduce the emission of blue light below 455 nm\u003csup\u003e29\u003c/sup\u003e. As a result, the spectral tuning window is subject to strict constraints: the \u003cem\u003e\u0026lambda;\u003c/em\u003eₘₐₓ should not exceed 467 nm, while the onset wavelength must stay above 455 nm. Previous attempts to narrow emission linewidths have mainly focused on extending the multiple-resonance frameworks via multi-boron-fused polycyclic aromatic hydrocarbons and the state-of-the-art quadruple-borylated emitter could realize a \u003cem\u003e\u0026lambda;\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e of 458\u0026thinsp;nm with a FWHM of only 12\u0026thinsp;nm in solution\u003csup\u003e30\u003c/sup\u003e. Yet, most emitters struggle to meet the above constraints, and they also exhibit increased molecular weight and enhanced intermolecular interactions\u0026mdash;both of which compromise thermal stability and device longevity. \u003csup\u003e30,31\u003c/sup\u003e. Although steric substitution or cyclic protective structures have been explored to suppress aggregation, few of them could result in adequate stability\u003csup\u003e32,33\u003c/sup\u003e. Therefore, achieving a balance between ultra narrowband emission, superior molecular stability, and deep-blue color remains a major challenge.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo overcome these constraints, we departed from the conventional design of large planar MR frameworks and developed an advanced molecular architecture characterized by a highly twisted helical configuration with spatially confined frontier molecular orbitals. Challenging the conventional wisdom that twisted molecules inevitably impair color purity via structural distortion, our design strategically circumvents this limitation by precisely engineering orbital confinement to decouple radiative transitions from helical deformation while leveraging this framework to mitigate carbon-hydrogen (C\u0026ndash;H) bond repulsion and suppress molecule aggregation. Benefiting from the weakened intermolecular interactions, this emitter successfully showed almost the same spectra in high polarity phosphor-sensitized fluorescence (PSF) and low polarity TTA systems, while also delivering high efficiency and prolonged operational lifetime in their respective configurations. This allows us to develop a novel unicolor hybrid-tandem architecture concept that synergistically integrates complementary exciton-utilization mechanisms: PSF unit for 100% internal quantum efficiency and TTA unit for enhanced operational lifetime. This innovative design overcomes the fundamental efficiency-lifetime trade-off inherent in conventional homogeneous tandem deep-blue OLEDs while maintaining perfect spectral uniformity. The proof-of-the-concept device achieved a high external quantum efficiency of 39.7%, an LT90 of 539 h at an L\u003csub\u003e0\u003c/sub\u003e of 1,000 cd m\u003csup\u003e-2\u003c/sup\u003e, an ultra-narrow electroluminescence with FWHM of only 14 nm, and CIE coordinates of (0.13, 0.10). We further reveal that the stacking sequence of emitting units significantly influences operational lifetime\u0026mdash;a two‐fold difference attributable to disparities in outcoupling efficiency and photoelectric co‐aging mechanisms. It is worth noting that our device performances even surpass recently reported state-of-the-art stable deep-blue phosphorescent tandem OLEDs in both device efficiency and stability with even bluer color\u003csup\u003e23\u003c/sup\u003e, representing the potential toward commercially viable ultrapure-blue OLEDs.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eMolecular design and theoretical calculation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFig. 1 illustrates the molecular design strategy proposed in this work. To gain deep insight into the relationship between molecular structure and photophysical properties, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were carried out at the B3LYP/6-31G (d, p) level. The selection of an appropriate parent molecule is crucial. Previous studies have shown that double-borylated \u0026pi;-skeletons with meta-substituted B\u0026ndash;Ar\u0026ndash;B fragments represent a highly promising approach for achieving narrow FWHM values of \u0026lt;20 nm, as exemplified by \u003cem\u003ev\u003c/em\u003e-DABNA and BD-3Cz (also referred to as BBCZ-SB)\u003csup\u003e34,35\u003c/sup\u003e. Compared to \u003cem\u003ev\u003c/em\u003e-DABNA, BD-3Cz exhibits a convergent structure and contains one fewer nitrogen atom in the fused core, resulting in a wider energy gap and a hypsochromic shift in emission. However, theoretical calculation indicates a high vibration intensity for BN-3Cz at frequency of 1573.6 cm⁻\u0026sup1;, leading to a relatively broad FWHM and a pronounced high-energy shoulder peak. This strong vibrational mode primarily stems from stretching vibrations of the 1- and 3-positioned carbazole units, driven by steric repulsion between adjacent C-H bonds-as indicated by large displacement vectors pushing these hydrogens away from each other. It is therefore envisioned that mitigating this repulsion could lead to a narrower emission spectrum and reduced shoulder intensity.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn contrast to conventional approaches that extend planar multiple-resonance skeletons through additional boron incorporation, we proposed an innovative strategy employing a highly twisted helical configuration to eliminate C-H bond repulsion. As shown in Fig. 1a, we strategically replaced two carbazole units in BD-3Cz with 12H-benzofuro [3,2-a] carbazole (CzO) segments to create our target molecule BD-Cz-2CzO. The CzO group was specifically selected for its nonlinear architecture, which would restrict molecular extension to maintain deep-blue emission and provide unique reaction sites for helical structure formation. As detailed in the Supplementary Information, BD-Cz-2CzO was efficiently synthesized in three steps from commercially available precursors. The synthesis involved a classical directional nucleophilic substitution coupling followed by a high-yield \u0026quot;one-pot\u0026quot; lithiation-diboronation reaction. Comprehensive structural characterization was performed using nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. For comparative studies, we also synthesized BD-3Cz and BD-2Cz-CzO as reference compounds. The optimized molecule structures of those compounds in ground states (S\u003csub\u003e0\u003c/sub\u003e) were shown in Supplementary Fig. 1, clearly demonstrating the successful formation of a helical configuration for BD-Cz-2CzO. Quantitative analysis revealed increasing molecular planarity parameters (MPP) of 1.12 \u0026Aring;, 1.37 \u0026Aring;, and 1.57 \u0026Aring; for BD-3Cz, BD-2Cz-CzO, and BD-Cz-2CzO, respectively (Supplementary Fig. 2). This progressive increase in MPP values confirms our design strategy of enhancing molecular twist through CzO group incorporation.\u003c/p\u003e\n\u003cp\u003eThe photophysical properties of all three compounds were measured in diluted toluene, and the collected results are presented in Fig.1b. Remarkably, BD-Cz-2CzO exhibits an ultra-narrowband deep-blue emission peak at 460 nm with a\u0026nbsp;recorded FWHM of merely 12 nm (0.07 eV). To the best of our knowledge, this narrow FWHM is comparable to, or even surpasses, that of state-of-the-art quadruple-borylated deep-blue emitters-particularly when compared using eV as the unit of measurement (Supplementary Table 1). The other two references, however, showed relatively large FWHMs of 16 nm and 14 nm for BD-3Cz and BD-2Cz-CzO, respectively. Notably, as the number of CzO groups increases, not only is the FWHM narrowed, but the shoulder intensity also decreases-from 0.18 in BD-3Cz and 0.15 in BD-2Cz-CzO to 0.10 in BD-Cz-2CzO. Moreover, given its strong absorption band at 455 nm as illustrated in Supplementary Fig. 3, BD-Cz-2CzO displays an exceptionally small Stokes shift of only 5 nm, suggesting its minimal vibrational coupling between the S\u003csub\u003e0\u003c/sub\u003e and S\u003csub\u003e1\u003c/sub\u003e states and the minimal vibrational relaxation in the singlet excited state (S\u003csub\u003e1\u003c/sub\u003e). Considering the large MPP value of BD-Cz-2CzO aforementioned, our findings reveal a deviation from conventional photophysical principles: while molecular twisting is typically associated with spectral broadening, BD-Cz-2CzO demonstrates an inverse relationship, exhibiting the most pronounced helical distortion yet the narrowest emission spectrum. This counterintuitive phenomenon is further corroborated by root mean square displacement (RMSD) analysis, which shows progressively increasing values from 0.053 (BD-3Cz) to 0.063 (BD-2Cz-CzO) to 0.073 (BD-Cz-2CzO) between S\u003csub\u003e0\u003c/sub\u003e and S\u003csub\u003e1\u003c/sub\u003e states. And as illustrated in Fig. 1c, the main structural deformation of BD-Cz-2CzO primarily localized at the benzofuran segment of the helical structure.\u0026nbsp;These RMSD values quantitatively confirm the enhanced structural deformation upon excitation that accompanies the increased molecular twist. This apparent paradox between structural distortion and spectral narrowing highlights the unique photophysical behavior enabled by our helical molecular design.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo elucidate the structure-property relationships of these three molecules, we conducted detailed theoretical calculations of their electronic properties. Fig.1d shows the electron density distributions of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), revealing that the HOMO is localized at ortho- and para-positions relative to the electron-donating nitrogen atoms, while the LUMO occupies meta-positions to nitrogen and ortho/para-positions to the electron-withdrawing boron atoms. These distributions exhibit characteristic hybrid \u0026pi;/non-bonding orbital features typical of MR emitters\u003csup\u003e36-38\u003c/sup\u003e. Hole-electron analysis using Multiwfn software\u003csup\u003e39,40\u0026nbsp;\u003c/sup\u003efurther demonstrated that the S\u003csub\u003e1\u003c/sub\u003e states of all three compounds exhibits partial intramolecular short-range charge-transfer (SRCT) characteristics (Supplementary Fig. 4), with large oscillator strengths (\u003cem\u003ef\u003c/em\u003e) of 0.522, 0.427, and 0.305 for BD-3Cz, BD-2Cz-CzO, and BD-Cz-2CzO, respectively. A key distinction emerges in the frontier orbital distributions: unlike BD-3Cz where orbitals delocalize across the entire skeleton, BD-2Cz-CzO and BD-Cz-2CzO show negligible HOMO/LUMO density on the benzofuran moiety of CzO donors. Fragment analysis of CzO revealed that its HOMO primarily resides on the carbazole unit (82.17%, Supplementary Fig. 5), which can be attributed to two factors: first, carbazole\u0026apos;s stronger electron-donating ability (electronegativity O (3.44)\u0026gt; N (3.04)\u0026gt; C (2.55)) results in a higher-lying HOMO; second, the oxygen atom\u0026apos;s strategic connection to the void carbon atom minimizes orbital overlap between benzofuran and carbazole. This is further supported by the calculated HOMO energies: CzO (-5.44 eV) closely matches carbazole (-5.46 eV) and is significantly higher than benzofuran (-5.98 eV). In BD-Cz-2CzO, boron\u0026apos;s strong electron-withdrawing nature further confines orbitals to carbazole segments, with benzofuran contributing minimally to both HOMO (4.74%) and LUMO (3.40%) distributions (Supplementary Fig. 6). Hole-electron analysis confirmed this localized character, showing the benzofuran segment contributes only 5.10 % to hole distribution and 2.54% to electron distribution during charge-transfer excitation (Supplementary Fig. 7). These results collectively demonstrate the effective orbital confinement in BD-Cz-2CzO, being away from the distortion-prone helical region. Therefore, though enlarging the geometric structural discrepancies between the S\u003csub\u003e0\u003c/sub\u003e and S\u003csub\u003e1\u003c/sub\u003e states, the distorted benzofuran-segment does not contribute to the radiative transition process and thus showed negligible influence on the spectra. Moreover, the limited orbital extension of the molecule also benefits to maintain blue emission without disturbing MR distributions.\u003c/p\u003e\n\u003cp\u003eTo further elucidate the origination of the smaller FWHM and the weaker shoulder of BD-Cz-2CzO, we calculated the reorganization energies (\u003cem\u003e\u0026lambda;\u003c/em\u003e) of all three compounds using the Molecular Materials Property Prediction Package (MOMAP)\u003csup\u003e41,42\u003c/sup\u003e. Contrary to the RMSD results, we observed a progressive decrease in \u003cem\u003e\u0026lambda;\u003c/em\u003e values from BD-3Cz to BD-2Cz-CzO to BD-Cz-2CzO (Fig.1e). This trend directly correlates with the narrowing of emission linewidths, as \u003cem\u003e\u0026lambda;\u003c/em\u003e more accurately reflects the structural rearrangement during S\u003csub\u003e1\u003c/sub\u003e\u0026rarr;S\u003csub\u003e0\u003c/sub\u003e transitions. Detailed vibrational mode analysis in Fig.1f revealed that the key differences emerge in the high-frequency region (\u0026gt;1000 cm⁻\u0026sup1;), which critically influences both spectral width and shoulder intensity. The introduction of CzO groups systematically reduces vibrational coupling in this region, particularly for modes associated with C-H wagging (1573.6 cm⁻\u0026sup1; in BD-3Cz, \u003cem\u003e\u0026lambda;\u003c/em\u003e=77.5 cm⁻\u0026sup1;). This reduction is most pronounced in BD-Cz-2CzO, where the helical structure completely eliminates steric repulsion between adjacent hydrogens, yielding a negligible \u003cem\u003e\u0026lambda;\u003c/em\u003e of 2.6 cm⁻\u0026sup1; at 1574.1 cm⁻\u0026sup1;. Complementary Huang-Rhys factor analysis (Fig. 1g) confirmed these findings, showing significantly reduced values in the high-frequency region for BD-Cz-2CzO compared to the reference compounds. These results demonstrate that our helical molecular design achieves ultra-narrow emission with suppressed shoulder through two key mechanisms: one is strategic localization of frontier orbitals away from distortion-prone regions to decouple radiative transitions from structural deformation, and another is effective mitigation of C-H repulsion through the twisted framework. This approach represents a significant departure from conventional planar designs, opening new possibilities for engineering high-performance narrowband emitters.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization and photophysical properties\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSingle crystals of BD-2Cz-CzO and BD-Cz-2CzO were successfully grown through slow solvent evaporation in dichloromethane and characterized by single-crystal X-ray diffraction (Fig. 2a, 2b and Supplementary Tables 2-3). Structural analysis revealed fundamentally different packing behaviors between these two emitters. The BD-2Cz-CzO with only one-side twisting shows twist angles of 29.1\u0026deg; (CzO-benzene) and 20.9\u0026deg; (carbazole-benzene), and a 3.5 \u0026Aring; separation between benzofuran and carbazole units. Its crystal packing features both head-to-head and tail-to-tail arrangements with intermolecular distances of 3.4 \u0026Aring; and 3.5 \u0026Aring;, respectively. More significantly, the overlapping regions in this packing configuration coincide with areas of electronic transition, promoting intermolecular orbital interactions that can lead to spectral broadening and aggregation-caused quenching at elevated doping concentrations. On the contrary, the dual-side twisting BD-Cz-2CzO exhibits distinct structural parameters with dihedral angles of 34.2\u0026deg; and 34.1\u0026deg; between its CzO units and central benzene ring, with benzofuran segments separated by 3.6 \u0026Aring;. This molecule adopts a head-to-tail helical packing arrangement with an average intermolecular distance of 3.4 \u0026Aring;. Though the existence of \u003cem\u003e\u0026pi;\u003c/em\u003e-\u003cem\u003e\u0026pi;\u003c/em\u003e interactions, this molecule adopts a head-to-tail helical packing motif, with predominant intermolecular contacts occurring at the tail regions of the CzO units where electronic transitions are minimal. This packing mode effectively separates adjacent MR emitting-cores in spatial, benefiting the suppression of aggregation-induced spectral broadening and molecule stability issues. The striking contrast between these molecular architectures - the moderately twisted BD-2Cz-CzO versus the highly twisted helical BD-Cz-2CzO - provides clear evidence that the degree of molecular distortion plays a decisive role in determining anti-aggregation behavior.\u003c/p\u003e\n\u003cp\u003eTo evaluate the anti-aggregation capability of the helical structure, we examined doped films with varying concentrations (1-4 wt%) in SiCzCz: SiTrzCz2 (65: 35) host matrices. While BD-3Cz-doped films exhibited significant spectral broadening (FWHM up to 30 nm) and greatly enhanced shoulder intensity, and BD-2Cz-CzO showed moderate improvement, BD-Cz-2CzO maintained nearly identical deep-blue emission (\u003cem\u003e\u0026lambda;\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e of 466 nm, FWHM of 14 nm) across all doping concentrations (Fig. 2c-e). This exceptional spectral stability, accompanied by consistently high photoluminescence quantum yields (PLQYs) of \u0026gt;98%, directly demonstrates the superior anti-aggregation effect of the highly twisted helical architecture, which effectively increases intermolecular distances between emitting cores. Transient photoluminescence analysis of 2 wt% BD-Cz-2CzO doped films at room temperature revealed distinct decay components with a prompt lifetime of 9 ns and delayed lifetime of 52 \u0026mu;s. The remarkably high radiative decay rate (\u003cem\u003ek\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e) of 8.4\u0026times;10\u003csup\u003e7\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e should benefit from the efficient SRCT transition characteristic with large \u003cem\u003ef\u003c/em\u003e value. Meanwhile, the moderate reverse intersystem crossing rate (\u003cem\u003ek\u003c/em\u003e\u003csub\u003eRISC\u003c/sub\u003e) of 2.3\u0026times;10\u003csup\u003e4\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e is consistent with the behavior observed in most multiple-resonance emitters (Supplementary Fig. 9 and Supplementary Table 4)\u003csup\u003e43\u003c/sup\u003e.\u0026nbsp;This \u003cem\u003ek\u003c/em\u003e\u003csub\u003eRISC\u003c/sub\u003e value directly correlates with the measured singlet-triplet energy gap (\u0026Delta;\u003cem\u003eE\u003c/em\u003e\u003csub\u003eST\u003c/sub\u003e) of 0.17 eV, as determined from low-temperature (77 K) fluorescence and phosphorescence spectra in Supplementary Fig. 10, which yielded singlet and triplet state energies of 2.77 eV and 2.60 eV, respectively.\u003c/p\u003e\n\u003cp\u003eBesides, the helical molecular architecture favors excellent thermal stability. Thermogravimetric analysis (TGA) reveals a high decomposition temperature (T\u003csub\u003ed\u003c/sub\u003e) of 523 \u0026deg;C at 5% weight loss (Supplementary Fig. 11), while the relatively low molecular weight (\u0026lt;900) ensures good vapor deposition processability. Crucially, the material maintains exceptional thermal stability during prolonged heating, as evidenced by high-performance liquid chromatography (HPLC) analysis showing \u0026gt;99.9% purity after 240 hours of continuous heating at 360\u0026deg;C (the operational evaporation temperature) (Supplementary Fig. 12). This combination of properties stands in stark contrast to conventional planar extended skeletons, which typically suffer from thermal degradation and compromised device longevity.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePerformance of single-unit OLEDs\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOwing to its excellent photophysical properties, BD-Cz-2CzO was further evaluated in single-unit devices based on TTA (S-TTA) and PSF (S-PSF) emitting mechanisms with device structures of ITO/ HATCN (5 nm)/ NPB (30 nm)/ BCzPh (10 nm)/ \u0026alpha;,\u0026beta;-ADN: BD-Cz-2CzO (1-4 wt%, 30 nm)/ CzPhPy (10 nm)/ DPPyA: Liq (1:1, 30 nm)/ LiF (0.5 nm)/ Al (150 nm) and ITO/ HATCN (5 nm)/ NPB (30 nm)/ SiCzCz (10 nm)/ SiCzCz: SiTrzCz2: BD-02: BD-Cz-2CzO (65 wt%:35 wt%:10 wt%:1-4 wt%, 30 nm)/ SiTrzCz2 (10 nm)/ DPPyA: Liq (1:1, 30 nm)/ LiF (0.5 nm)/ Al (150 nm), respectively. The device structures and energy levels have been provided in Fig.3a and 3b. The blue phosphorescent material BD-02 in the emissive layer (EML) was utilized as a sensitizer due to its favorable PL spectral overlap with the absorption of the BD-Cz-2CzO (Supplementary Fig.13)\u003csup\u003e9\u003c/sup\u003e, ensuring sufficient energy transfer to maintain a narrowband spectral distribution and harvest triplet excitons to attain unit internal quantum efficiency (IQE).\u003c/p\u003e\n\u003cp\u003eBoth type devices showed sharp electroluminescence (EL) emission from the final emitter with\u0026nbsp;\u003cem\u003e\u0026lambda;\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e of 463 nm, FWHM of 13 nm and CIE\u003csub\u003ey\u003c/sub\u003e of 0.10 for S-TTA device while\u0026nbsp;\u003cem\u003e\u0026lambda;\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e of 464 nm, FWHM of 14 nm and CIE\u003csub\u003ey\u003c/sub\u003e of 0.11 for S-PSF device (Fig. 3c). It is interestingly to note that nearly identical EL spectra were observed for both devices. Typically, owing to the existence of solid-state solvation effect and uncomplete energy transfer,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eEL spectra of MR emitters would show relatively broader FWHM and redshifted\u0026nbsp;\u003cem\u003e\u0026lambda;\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e in the high polarity PSF device compared with the low polarity TTA system. The nearly identical EL spectra of both devices should arise from, on one hand, the twisted helical structure of our emitter, suppressing molecular interactions, and on the other hand, complete energy transfer owing to its extremely small stokes-shift and thus guarantee efficient sensitizer emission-emitter absorption overlap. This can be reflected by the fact that as the concentration of the emitter increased from 1 wt% to 4 wt%, all the devices achieved nearly identical deep-blue EL (Fig. 3c, and Supplementary Fig.14 and Supplementary Table 5). To the best of our knowledge, the observed extremely narrow EL spectra represents one of the narrowest emissions for MR emitters in OLEDs (Supplementary Table 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig.3d showed the EQE-luminance characteristics and\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003efor\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eS-TTA device, owing to the triplet recycle through TTA process, EQE\u003csub\u003emax\u003c/sub\u003e of 10.1% was obtained. While the optimal S-PSF device exhibited higher EQE\u003csub\u003emax\u003c/sub\u003e of 33.5% owing to its much higher internal quantum efficiency due to the sensitized process. Moreover, the high EQE also arises from the high horizontal emitting dipole orientation (\u003cem\u003e\u0026Theta;\u003c/em\u003e\u003csub\u003e//, max\u0026nbsp;\u003c/sub\u003e= 84%) of the emitter (Fig. 3e), which benefit light outcoupling. Excitingly, minimal efficiency roll-off was observed for S-PSF device with EQE of 27.9% at 1, 000 cd m\u003csup\u003e-2\u003c/sup\u003e, which outperforms other deep-blue emitters with significant roll-offs at high luminance in the literature. A plausible reason for this is that the high \u003cem\u003ek\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e of emitter could efficiently accelerate exciton radiative dynamics which avoiding exciton annihilations at high luminance.\u0026nbsp;The stability of both devices was evaluated with a fixed current at an initial luminance (L\u003csub\u003e0\u003c/sub\u003e) of 1, 000 cd m\u003csup\u003e-\u003c/sup\u003e\u0026sup2;, revealing LT90 of 676 h and 150 h for S-TTA and S-PSF devices (Fig.3f). To the best of our knowledge, both devices show the cutting-edge efficiency and lifetime\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ein their respective configurations at their specific colors\u003csup\u003e7\u003c/sup\u003e. The good stability could be attributed to the ultra-narrowband emission of the emitter to lower onset energy to reduce the proportion of high-energy photons of the emitter and mitigating the degradation probability of molecules in the excited state, ultimately leading to a longer lifetime.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eMoreover, the twisted structure of BD-Cz-2CzO enhance thermal stability and prevent the potential molecule interactions, and thus benefit operation stability. Previous works with extended MR skeletons would deteriorate molecule thermal stability and increase the chance for molecule interactions and thus poor stability.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePerformance of uni-color hybrid tandem OLED\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;The nearly identical EL spectra and excellent performances of BD-Cz-2CzO in both S-PSF and S-TTA configurations enabled the development of the unicolor-hybrid-tandem (UHT) OLED concept, theoretically\u0026nbsp;integrating complementary advantages of high efficiency from PSF unit and long lifetime from TTA unit.\u0026nbsp;Fig.4a illustrated architectures of UHT devices and what deserves to mention is that two distinct configurations with inverted unit sequences can be fabricated: UHT-1 positions the PSF-unit closer to the light-emitting side, whereas UHT-2 adopts the opposite arrangement. Moreover, both device configurations employed an experimentally validated charge generation layer known for its stability and efficiency\u003csup\u003e44,45\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig.4b illustrates the identical sharp EL spectra of both devices with\u0026nbsp;\u003cem\u003e\u0026lambda;\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e at 464 nm, FWHMs of 14 nm and deep-blue CIE\u003csub\u003ey\u0026nbsp;\u003c/sub\u003ecoordinates of 0.10 and 0.11, respectively. This spectrum represents the narrowest one among reported deep-blue tandem OLEDs\u003csup\u003e15,23,30\u003c/sup\u003e.\u003cstrong\u003e\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u003c/strong\u003eMoreover, this\u0026nbsp;\u003cem\u003e\u0026lambda;\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e is shorter than the theoretical 467 nm for BT.2020 blue and negligible emission below 455 nm owing to its smallest FWHM among reported deep-blue tandem devices, therefore potentially satisfying the constraint for physiologically friendly wide-color gamut displays. As shown in Supplementary Fig.15, the nearly identical current density-voltage characteristics observed in both devices indicates highly consistent charge transport properties across the two hybrid tandem architectures. This further suggests that the exciton recombination processes remain essentially equivalent between the two configurations, ultimately yielding matching internal quantum efficiencies (IQEs). The EQE-luminance characteristics in Fig.4c, however, revealed a slightly higher EQE\u003csub\u003emax\u003c/sub\u003e of 46.3% for UHT-1 while 39.7% for UHT-2, indicating distinct light outcoupling behaviors between the two architectures. Notably, both devices exhibited minimal efficiency roll-off, retaining EQEs of 42.4% and 37.2% at a practical luminance of 1,000 cd\u0026middot;m\u0026sup2; for UHT-1 and UHT-2, respectively. The angular dependence of EL intensity was systematically investigated as documented in Supplementary Fig.16, which basically followed the Lambertian distribution, validating the high device efficiency. The operational stability of both devices was evaluated under constant current driving at an initial luminance of 1,000 cd/m\u0026sup2;. The measured LT90 values reached 263 hours for UHT-1 and 539 hours for UHT-2. To the best of our knowledge, the UHT-2 device represents a breakthrough with the longest LT90 reported so far to date for deep-blue OLED exceeding 20% EQE, not to mention its small CIE\u003csub\u003ey\u003c/sub\u003e of only 0.10 (Fig.4d, 4e, and Supplementary Table 6). The UHT devices demonstrate superior performance when compared with state-of-the-art homogeneous tandem phosphorescent OLEDs\u003csup\u003e23\u003c/sup\u003e.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eFor comparative study, we fabricated two conventional tandem OLEDs: T-PSF (dual S-PSF units) and T-TTA (dual S-TTA units). As shown in Supplementary Fig.17 and Supplementary Table.7, these control devices exhibited the characteristic efficiency-stability trade-off: the T-PSF configuration achieved a higher EQE\u003csub\u003emax\u003c/sub\u003e of 67.7% but limited operational stability (LT90 of 228 h), whereas the T-TTA architecture showed superior lifetime (LT90 of 927 h) but significantly lower efficiency (EQE\u003csub\u003emax\u003c/sub\u003e of 21.8%). This marked contrast in performance metrics conclusively demonstrates the potential of the UHT concept in resolving the long-standing efficiency-stability compromise for deep-blue OLED applications.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo investigate the underlying mechanism responsible for the substantial lifetime variation between the two hybrid tandem device configurations, we performed systematic optical simulations to analyze\u0026nbsp;their respective optical modes as illustrated in Supplemntary Fig. 18.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eA distinct refractive index profiles between the two architectures was obtained, which could be attributed to the fact that while both configurations maintain identical charge transport layers, their EMLs and charge blocking layers exhibit markedly different refractive index, leading to variations in microcavity resonance characteristics and optical path lengths to the outcoupling substrate (Supplemntary Fig. 19). Specifically, in the UHT-1 configuration, the higher refractive index EML and blocking layers of the TTA-unit enhance interfacial reflections, consequently reducing the TTA-unit\u0026apos;s emission contribution through intensified surface plasmon polariton (SPP)\u003csup\u003e46\u003c/sup\u003e, substrate and waveguide modes.\u0026nbsp;Conversely, the PSF-units in this architecture benefit from their greater distance from the cathode, which substantially reduces SPP mode losses and thereby increases their relative contribution to total emission. The UHT-2 architecture demonstrates the opposite optical behavior. By positioning the TTA-unit away from the cathode, SPP mode losses are effectively minimized. Furthermore, the proximity to the anode, combined with favorable refractive index matching between the emitting/blocking layers and the transparent ITO substrate, significantly enhances light extraction efficiency. This optimized configuration allows the TTA-unit to contribute more substantially to the overall emission in UHT-2, while the PSF-unit in this architecture suffers from increased SPP losses and consequently reduced its emission contribution. To visualize this effect quantitatively, we introduced a parameter termed the relative light outcoupling efficiency (Fig.4f and 4g), denoted as \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003eout, relative\u003c/sub\u003e, defined as the ratio of the light outcoupling efficiency of the TTA-unit to that of the PSF-unit within the hybrid tandem device. This quantity is expressed as:\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cimg src=\"data:image/png;base64,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\" style=\"width: 184px; height: 55.2px;\" width=\"184\" height=\"55.2\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003eout\u003c/sub\u003e,\u003csub\u003eTTA\u003c/sub\u003e and \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003eout\u003c/sub\u003e,\u003csub\u003ePSF\u003c/sub\u003e represent the absolute outcoupling efficiencies of the TTA-unit and PSF-unit, respectively. Based on optical simulations, the calculated \u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003eout,relative\u003c/sub\u003e was 0.78 for the UHT-1 device and 1.34 for UHT-2. These results indicate that the TTA-unit possesses higher contribution to the total emission in the UHT-2 architecture, which is inconsistent with the lower EQE but better operation stability of UHT-2 device, underscoring the pronounced influence of unit positioning on the overall emission balance in the hybrid tandem structure.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMeanwhile, in tandem devices, due to the small stokes-shift of ultranarrowband emitter, there would generate self-absoprtion and thus photoelectric co-aging. And the different duration of TTA and PSF units would also induce different photoelectric co-aging discrepancy compared with the tandem devices with the same emitting-units.\u0026nbsp;Here, the photoelectric tests of S-PSF and S-TTA devices with an initial luminance of 1000 cd m\u003csup\u003e-2\u003c/sup\u003e under continuous light irradiation with a peak wavelength of 464 nm and a power density of approximately 1 mW cm\u003csup\u003e-2\u003c/sup\u003e were conducted to further elucidate the issue of lifetime differences. As shown in Fig.4h , the luminance of S-PSF device significantly dropped to below 90% after 60 h, while the luminance of S-TTA device still maintained over 98% of the initial luminance in the same test duration. This notable performance disparity also led to the differences in the lifetime of hybrid tandem devices as the photoelectrically unstable PSF-unit contribute higher to the EL of UHT-1 device, resulting in the relatively shorter lifetime of UHT-1 device. \u0026nbsp;\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, contradicting conventional assumptions about twisted molecular skeletons compromising color purity, an innovative MR emitter featuring a highly-twisted helical molecular configuration with spatially-confined frontier molecular orbitals was developed for stable and ultra-narrowband emission. This unique design successfully decouples radiative transitions from structural distortions while effectively mitigating spectral broadening caused by both C-H bond repulsion and molecular aggregation, demonstrating exceptional photophysical characteristics with a proper \u0026lambda;\u003csub\u003emax\u003c/sub\u003e of 460 nm and a FWHM of 12 nm in solution. Remarkably, this emitter maintains nearly identical emission spectra in both PSF and TTA systems with cutting-edge performances. This enables the realization of unicolor hybrid-tandem OLED concept to integrates complementary exciton-harvesting mechanisms to simultaneously address the fundamental efficiency-lifetime trade-off while preserving spectral uniformity. The optimized device achieves outstanding performance metrics with an external quantum efficiency of 39.7%, a remarkable long LT90 of 539 hours at 1,000 cd\u0026middot;m⁻\u0026sup2;, an EL FWHM of 14 nm and CIE\u003csub\u003e\u0026shy;y\u003c/sub\u003e of 0.10 concurrently. These findings may provide valuable insights for future development of high-performance deep-blue OLED materials and devices. Recently, LG Display announced a hybrid-tandem device incorporating a phosphorescent and a fluorescent unit, highlighting the growing commercial interest in this approach. (https://news.lgdisplay.com/en/2025/05/final-step-to-achieving-dream-oled-lg-display-becomesworlds-first-to-verify-commercialization-ofblue-phosphorescent-oled-panels/.) However, their design faces inherent challenges of spectral mismatch due to the different final emitters in each unit. Our architecture overcomes this limitation by employing the same final emitter in both units, thereby ensuring perfect spectral uniformity (i.e., unicolor emission) while preserving all performance advantages, representing a critical advancement in the pursuit of eventual commercialization.\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information file. The X-ray crystallographic coordinates for structures reported in this study have been deposited at the CCDC under deposition numbers 2484150 and 2484151. These data can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk/data_request/cif.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Key Basic Research and Development Program of China (Grant no. 2024YFB361210), the National Science Fund of China (Grant No. 22135004 and 52222308).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eL.D. and D.Z. supervised the project and conceived the conceptual idea and designed the experiments. C.C. synthesized and characterized the MR emitter. C. C., M.M., and C.L. performed the theoretical calculations, photophysical characterization, OLED fabrication, and measurement. D.Z. and L.D. analyzed the results and wrote the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eTang, C. W. \u0026amp; VanSlyke, S. A. Organic electroluminescent diodes. \u003cem\u003eAppl. Phys. Lett.\u003c/em\u003e \u003cstrong\u003e51\u003c/strong\u003e, 913-915 (1987).\u003c/li\u003e\n\u003cli\u003eHong, G.\u003cem\u003e et al.\u003c/em\u003e A Brief History of OLEDs\u0026mdash;Emitter Development and Industry Milestones. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e33\u003c/strong\u003e, 2005630 (2021).\u003c/li\u003e\n\u003cli\u003eMonkman, A. Why Do We Still Need a Stable Long Lifetime Deep Blue OLED Emitter? \u003cem\u003eACS Appl. Mater. Interfaces\u003c/em\u003e \u003cstrong\u003e14\u003c/strong\u003e, 20463-20467 (2022).\u003c/li\u003e\n\u003cli\u003eIm, Y.\u003cem\u003e et al.\u003c/em\u003e Recent Progress in High‐Efficiency Blue‐Light‐Emitting Materials for Organic Light‐Emitting Diodes. \u003cem\u003e Adv. 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A.\u003cem\u003e et al.\u003c/em\u003e Plasmonic enhancement of stability and brightness in organic light-emitting devices. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e585\u003c/strong\u003e, 379-382 (2020).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eGeneral Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll starting materials and\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ereaction solvent (ultra-dry) were obtained from commercial suppliers and were used without further purification. Further drying and distillation of commercially available ultra-dry solvents are required before use.\u003c/p\u003e\n\u003cp\u003eThe \u003csup\u003e1\u003c/sup\u003eH NMR and \u003csup\u003e13\u003c/sup\u003eC NMR spectra were obtained in deuterated solution utilizing a JEOL JNM-ECS400 NMR spectrometer. MALDI-TOF-MS data were performed on a Shimadzu AXIMA Performance MALDI-TOF instrument in positive detection modes. Thermogravimetric analysis (TGA) was conducted using a HITACHI STA200 instrument under a nitrogen atmosphere. Single-crystal X-ray diffraction data were recorded on a Bruker D8 Venture X-ray single-crystal diffractometer using Cu/Ga K\u0026alpha; radiation (\u0026lambda; = 1.54178/1.34139 \u0026Aring;) for the compound. The structure was solved using SHELXT and refined with SHELXL. All non-hydrogen atoms were refined anisotropically. The positions of hydrogen atoms were calculated and refined isotropically. UV-vis absorption spectra were recorded on a UV-2600 (Shimadzu) spectrophotometer. Photoluminescence (PL) spectra were acquired using a Hitachi F-7000 fluorescence spectrophotometer. The lifetimes of prompt fluorescence and delayed fluorescence were measured on an Edinburgh Fluorescence Spectroscopy FLS1000. Absolute PL quantum yields (PLQYs) were obtained with an absolute photoluminescence quantum yield measurement system Hamamatsu C9920-03G in an integrating sphere.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eQuantum Chemical Calculations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll simulation calculations were conducted using the Gaussian 16 program package. The ground-state geometries were optimized via density functional theory (DFT) calculations in vacuum, employing the B3LYP hybrid functional and the 6-31G (d,p) basis set. Based on the optimized ground-state geometries, time-dependent DFT (TD-DFT) excited-state analyses were performed at the B3LYP/6-31G(d,p) level. Franck-Condon analyses of the emission spectra were performed according to the literature using the Gaussian 16 package\u003csup\u003e47\u003c/sup\u003e. The MPP values and RMSDs of the optimized structures at S\u003csub\u003e0\u003c/sub\u003e and S\u003csub\u003e1\u003c/sub\u003e states were analyzed by Visual Molecular Dynamics (VMD) software\u003csup\u003e48\u003c/sup\u003e. The Huang-Rhys (HR) factors and reorganization energies were calculated using the MOMAP software. Optical simulations were conducted using the methods in Supporting Information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDevice Fabrication and Characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll compounds underwent temperature gradient sublimation under high vacuum before use with a purity exceeding 99.9%. Organic light-emitting diodes (OLEDs) were fabricated on glass substrates coated with indium tin oxide (ITO), with multiple organic layers sandwiched between the transparent ITO anode at the bottom and the metal cathode at the top.\u003c/p\u003e\n\u003cp\u003eBefore device fabrication, the ITO glass substrates were carefully pre-cleaned. All material layers were deposited via vacuum evaporation in a vacuum chamber with a base pressure of 10\u003csup\u003e-5\u0026nbsp;\u003c/sup\u003etorr. The deposition system allows the fabrication of the complete device structure in a single vacuum pumping cycle without breaking the vacuum. The deposition rate of organic layers was maintained at 0.5 ~ 1 \u0026Aring;/s. Doping was achieved through co-evaporation from separate evaporation sources with different evaporation rates.\u003c/p\u003e\n\u003cp\u003eThe current density, voltage, luminance, external quantum efficiency (EQE), electroluminescent spectra, and other characteristics were measured simultaneously using a Keithley 2400 source meter and an absolute EQE measurement system in an integrating sphere. The EQE measurement system is Hamamatsu C9920-12, equipped with a Hamamatsu PMA-12 Photonic Multichannel Analyzer C10027-02, which has a maximum detection wavelength of 1100 nm.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReferences\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e47\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Santoro, F., Lami, A., Improta, R., Bloino, J. \u0026amp; Barone, V. Effective method for the computation of optical spectra of large molecules at finite temperature including the Duschinsky and Herzberg\u0026ndash;Teller effect: The Qx band of porphyrin as a case study. \u003cem\u003eJ. Chem. Phys.\u003c/em\u003e \u003cstrong\u003e128\u003c/strong\u003e, 224311 (2008).\u003c/p\u003e\n\u003cp\u003e48\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Humphrey, W., Dalke, A. \u0026amp; Schulten, K. VMD: Visual molecular dynamics. \u003cem\u003eJ. Mol. Graphics\u003c/em\u003e \u003cstrong\u003e14\u003c/strong\u003e, 33-38 (1996).\u003c/p\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable1\u003c/strong\u003e |\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eSummarized performance of OLEDs\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"640\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11.8565%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDevices\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.33229%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e\u0026lambda;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eEL\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csup\u003ea\u003c/sup\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e(nm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.67239%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFWHM (nm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.7847%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eEQE\u003csup\u003eb\u003c/sup\u003e\u003csub\u003emax/1000/5000\u003c/sub\u003e (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.3807%;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePE\u003csup\u003ec\u003c/sup\u003e\u003csub\u003emax/1000/5000\u003c/sub\u003e (lm W\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2246%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCE\u003csup\u003ed\u003c/sup\u003e \u003csub\u003emax/1000/5000\u003c/sub\u003e (cd A\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.4805%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCIE\u003csup\u003ee\u003c/sup\u003e (\u003cem\u003ex\u003c/em\u003e,\u003cem\u003ey\u003c/em\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.26833%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLT\u003csub\u003e90\u003c/sub\u003e\u003csup\u003ef\u003c/sup\u003e (h)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11.8565%;\"\u003e\n \u003cp\u003eS-PSF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.33229%;\"\u003e\n \u003cp\u003e464\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.67239%;\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.7847%;\"\u003e\n \u003cp\u003e33.5/27.9/22.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.3807%;\"\u003e\n \u003cp\u003e33.2/18.4/10.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2246%;\"\u003e\n \u003cp\u003e31.7/25.8/20.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.4805%;\"\u003e\n \u003cp\u003e(0.13,0.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.26833%;\"\u003e\n \u003cp\u003e150\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11.8565%;\"\u003e\n \u003cp\u003eS-TTA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.33229%;\"\u003e\n \u003cp\u003e463\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.67239%;\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.7847%;\"\u003e\n \u003cp\u003e10.1/9.4/8.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.3807%;\"\u003e\n \u003cp\u003e8.9/5.4/3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2246%;\"\u003e\n \u003cp\u003e8.7/8.0/7.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.4805%;\"\u003e\n \u003cp\u003e(0.13,0.10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.26833%;\"\u003e\n \u003cp\u003e676\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11.8565%;\"\u003e\n \u003cp\u003eUHT-1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.33229%;\"\u003e\n \u003cp\u003e464\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.67239%;\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.7847%;\"\u003e\n \u003cp\u003e46.3/42.4/36.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.3807%;\"\u003e\n \u003cp\u003e22.8/15.2/10.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2246%;\"\u003e\n \u003cp\u003e42.4/37.8/31.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.4805%;\"\u003e\n \u003cp\u003e(0.13,0.11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.26833%;\"\u003e\n \u003cp\u003e263\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11.8565%;\"\u003e\n \u003cp\u003eUHT-2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.33229%;\"\u003e\n \u003cp\u003e464\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.67239%;\"\u003e\n \u003cp\u003e14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.7847%;\"\u003e\n \u003cp\u003e39.7/37.2/33.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.3807%;\"\u003e\n \u003cp\u003e20.8/14.4/10.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2246%;\"\u003e\n \u003cp\u003e40.1/36.7/32.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.4805%;\"\u003e\n \u003cp\u003e(0.13,0.10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.26833%;\"\u003e\n \u003cp\u003e539\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 11.8565%;\"\u003e\n \u003cp\u003eBD-02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.33229%;\"\u003e\n \u003cp\u003e462\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.67239%;\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.7847%;\"\u003e\n \u003cp\u003e24.8/23.9/21.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.3807%;\"\u003e\n \u003cp\u003e40.2/26.5/17.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2246%;\"\u003e\n \u003cp\u003e36.3/33.7/29.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.4805%;\"\u003e\n \u003cp\u003e(0.16,0.19)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.26833%;\"\u003e\n \u003cp\u003e249\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003ea\u0026nbsp;\u003c/sup\u003eEL peak wavelength. \u003csup\u003eb\u0026nbsp;\u003c/sup\u003eMaximum external quantum efficiency (EQE) and EQE at 1000 and 5000 cd m\u003csup\u003e-2\u003c/sup\u003e. \u003csup\u003ec\u0026nbsp;\u003c/sup\u003eMaximum power efficiency (PE) and PE at 1000 and 5000 cd m\u003csup\u003e-2\u003c/sup\u003e\u003csup\u003ed\u0026nbsp;\u003c/sup\u003eMaximum current efficiency (CE) and CE at 1000 and 5000 cd m\u003csup\u003e-2\u003c/sup\u003e. \u003csup\u003ee\u0026nbsp;\u003c/sup\u003eCIE coordinates. \u003csup\u003ef\u0026nbsp;\u003c/sup\u003eRecorded at an initial luminance of 1,000\u0026thinsp;cd\u0026thinsp;m\u003csup\u003e-2\u003c/sup\u003e.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7669597/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7669597/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Achieving efficient and stable deep-blue organic light-emitting diodes (OLEDs) with high color purity remains challenging, primarily due to the scarcity of blue emitters that simultaneously exhibit ultra-narrowband emission and high operational stability. Herein, we present a multiple-resonance emitter featuring a highly-twisted helical configuration with spatially-confined frontier molecular orbitals, thereby decoupling radiative transitions from structural distortion while mitigating spectral broadening from carbon–hydrogen bond repulsion and molecular aggregation. A sharp emission peaking at 460 nm with a full-width at half-maximum (FWHM) of only 12 nm is obtained in solution, which challenges the conventional belief that a twisted molecular skeleton compromises color purity. Remarkably, this emitter delivers cutting-edge performance with nearly identical spectra across emitting systems of varying polarity, enabling the realization of a unicolor hybrid-tandem OLED design that integrates complementary exciton-harvesting mechanisms to overcome the efficiency-lifetime trade-off inherent in conventional homogeneous tandem devices, while maintaining spectral uniformity. The targeted device concurrently achieves an external quantum efficiency of 39.7%, a lifetime of 539 hours to 90% of 1,000 cd·m⁻², a FWHM of 14 nm, and a chromaticity y-coordinate of 0.10. We further show that the stacking sequence of emitting units induces a twofold lifetime variation, which mainly arises from differences in outcoupling efficiency and photoelectric co-aging. This co-engineering strategy constitutes a substantial advance toward commercially viable ultrapure-blue OLED displays.","manuscriptTitle":"Ultra-Narrowband Helical Emitter with Frontier Orbital Confinement for Stable Deep-Blue Hybrid-Tandem Organic Light-emitting Diodes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-03 07:04:56","doi":"10.21203/rs.3.rs-7669597/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-materials","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"nmat","sideBox":"Learn more about [Nature Materials](http://www.nature.com/nmat/)","snPcode":"","submissionUrl":"","title":"Nature Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0c34e535-78b0-485d-96bb-90e8331f78d9","owner":[],"postedDate":"October 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":55633272,"name":"Physical sciences/Materials science/Materials for optics/Lasers, LEDs and light sources/Organic LEDs"},{"id":55633273,"name":"Physical sciences/Chemistry/Materials chemistry/Optical materials"}],"tags":[],"updatedAt":"2026-03-28T07:05:26+00:00","versionOfRecord":{"articleIdentity":"rs-7669597","link":"https://doi.org/10.1038/s41563-026-02529-2","journal":{"identity":"nature-materials","isVorOnly":false,"title":"Nature Materials"},"publishedOn":"2026-03-27 04:00:00","publishedOnDateReadable":"March 27th, 2026"},"versionCreatedAt":"2025-10-03 07:04:56","video":"","vorDoi":"10.1038/s41563-026-02529-2","vorDoiUrl":"https://doi.org/10.1038/s41563-026-02529-2","workflowStages":[]},"version":"v1","identity":"rs-7669597","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7669597","identity":"rs-7669597","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}