Halogen-Dependent Deep-Blue Circularly Polarized Emitters with Ultrahigh-Color-Purity Under High Pressure

Halogen-Dependent Deep-Blue Circularly Polarized Emitters with Ultrahigh-Color-Purity Under High Pressure | 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 Halogen-Dependent Deep-Blue Circularly Polarized Emitters with Ultrahigh-Color-Purity Under High Pressure Shuang-Quan Zang, Meng-En Sun, Fei Wang, Manman He, Ya-Ni Yang, and 9 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4687727/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Achieving free exciton (FE) emission in low-dimensional (2D, 1D, and 0D) metal halide perovskites is challenging due to the strong electron–phonon coupling effect induced by lead halide octahedral distortion. Herein, the FE emission behaviors of three new 2D chiral perovskites, ( R -3-XPEA) 2 PbBr 4 (PEA = phenethylamine, X = F, Cl, Br), were investigated under hydrostatic pressure. ( R -3-BrPEA) 2 PbBr 4 and ( R -3-ClPEA) 2 PbBr 4 exhibited high color–purity deep-blue circularly polarized luminescence (CPL) dominated by FE at pressures of 1.7 and 2.5 GPa, respectively, whereas ( R -3-FPEA) 2 PbBr 4 presented broadband warm-white CPL under high pressure. The structural analysis and theoretical calculation results demonstrated that pressure reduced the penetration depths of R -3-BrPEA + and R -3-ClPEA + into [PbBr 6 ] 4- inorganic frameworks by strengthening halogen···halogen (Br···Br and Cl···Cl) interactions between organic amines, resulting in smaller [PbBr 6 ] 4- octahedral distortion and weaker electron–phonon coupling in ( R -3-BrPEA) 2 PbBr 4 and ( R -3-ClPEA) 2 PbBr 4 . Thus, pressure-driven enhancement of halogen···halogen interactions was responsible for remarkable deep-blue CPL in ( R -3-BrPEA) 2 PbBr 4 and ( R -3-ClPEA) 2 PbBr 4 . Conversely, [PbBr 6 ] 4- octahedral distortion and strong electron–phonon coupling could not be effectively suppressed in ( R -3-FPEA) 2 PbBr 4 owing to the lack of halogen···halogen interactions, leading to the absence of deep-blue CPL. Our work gives a new insight into the intrinsic structure-property relationship between noncovalent interactions and the ultrahigh-color-purity emission behavior in chiral perovskites. Physical sciences/Chemistry/Inorganic chemistry Physical sciences/Chemistry/Materials chemistry Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Low-dimensional (2D, 1D, and 0D) metal halide perovskites (LDMHPs) have attracted considerable research attention for light-emitting diodes, nonlinear photonics, and detectors owing to their large exciton binding energy, diverse structures, and quantum confinement effects. 1 – 6 LDMHPs can be prepared by replacing cesium (Cs + ), formamidine (FA + ), or methylammonium (MA + ) in 3D metal halide perovskites with larger organic amine cations. 7 – 9 Bulky ammoniums exacerbate the structural distortion of the metal halide octahedron and induce a strong electron–phonon coupling effect in LDMHPs, 10 – 11 facilitating trapping of the free exction (FE) state by the distorted lattice and transformation into the self-trapped exciton (STE) state. 12 – 14 Thus, FE radiative recombination is the dominant process in 3D perovskites; however, it is scarce in LDMHPs. In contrast to broadband STE emission, radiative recombination results in narrower-band FE emission and higher luminescence color purity. FE-dominated luminescent materials are promising candidates for micro-nano lasers and highly sensitive sensors. 15 – 16 Effectively suppressing the large structural distortion and strong electron–phonon coupling effect in LDMHPs is expected to achieve FE emission and help to expand their applications. Quantum and dielectric confinement effects are often employed to tune FE emission characteristics in perovskites. 17 – 20 However, the key role of noncovalent interactions (i.e., hydrogen bonding and halogen···halogen interactions) is frequently ignored in the regulation of perovskite FE emission behavior. Halogen···halogen interactions, as a novel form of noncovalent interactions, have garnered growing interest among researchers due to their powerful ability to manipulate chiroptical activity, nonlinear optical response, and photoelectric conversion efficiency. 21 – 25 The ability of halogen···halogen interactions to control the structure and optical properties of materials makes it a potential strategy for FE emission manipulation in perovskites. Nevertheless, the inability to continuously and controllably regulate halogen···halogen interactions severely restricts their use in managing the FE emission behavior of LDMHPs. Therefore, convenient and efficient strategies based on halogen···halogen interactions are urgently needed to regulate the FE emission behavior of LDMHPs and systematically elucidate the intrinsic mechanism of noncovalent interactions driving FE emission. Hydrostatic pressure can be utilized as a powerful tool to efficiently manipulate the crystal and electronic structures and physicochemical properties of materials by shortening interatomic distances and increasing orbital overlap. 26 – 36 Currently, strengthening noncovalent interactions via the hydrostatic pressure effect is utilized to enhance luminescence, improve conductivity, narrow the band gap, and optimize chiroptical activity in perovskites, metal–organic frameworks, and organic molecules. 37 – 45 Thus, applying hydrostatic pressure to LDMHPs is expected to achieve FE emission through pressure-enhanced halogen···halogen interactions, thereby clarifying the structure–property relationship between structural distortion, noncovalent interactions, and FE emission behavior. Herein, three novel 2D chiral organic–inorganic halide perovskites ( R -3-XPEA) 2 PbBr 4 (PEA = phenethylamine, X = F, Cl, Br) with different halogen···halogen interactions were successfully prepared. Under ambient conditions, ( R -3-XPEA) 2 PbBr 4 crystals presented broadband yellow circularly polarized luminescence (CPL) dominated by STE emission. Variations in halogen···halogen interactions strength generated discrepancies in the pressure-dependent CPL spectral evolution of ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 . With increased pressure, ( R -3-BrPEA) 2 PbBr 4 and ( R -3-ClPEA) 2 PbBr 4 crystals exhibited remarkable piezochromic luminescence from yellow to cold-white to deep-blue. ( R -3-BrPEA) 2 PbBr 4 and ( R -3-ClPEA) 2 PbBr 4 exhibited narrow-band deep-blue (λ < 450 nm) CPL at pressures of 1.7 and 2.5 GPa, respectively. However, deep-blue CPL prevailed by FE states is absent in ( R -3-FPEA) 2 PbBr 4 . The in situ high-pressure angle-dispersive X-ray diffraction (ADXRD) results indicated that pressure weakened the penetration depths of R -3-BrPEA + and R -3-ClPEA + into the [PbBr 6 ] 4− octahedral frameworks by strengthening halogen···halogen (Br···Br and Cl···Cl) interactions between adjacent organic amines, which drove [PbBr 6 ] 4− to approach an ideal octahedral structure by suppressing the structural distortion of the inorganic sublattice. Density functional theory (DFT) calculations further demonstrated that reducing structural distortion weakened the electron–phonon coupling effect, promoting the de-trapping of the STE state back to the FE state. Conversely, structural distortion failed to be effectively prevented in ( R -3-FPEA) 2 PbBr 4 , which lacked halogen···halogen interactions, resulting in broadband STE emission. Our findings shed light on the intricate correlations between halogen···halogen interactions, structural distortion, and CPL performance in LDMHPs. Meanwhile, our work also provides a novel approach and experimental reference for the preparation of new deep-blue CPL materials with ultrahigh-color-purity. Results and Discussion Synthesis and characterization of ( R -3-XPEA) 2 PbBr 4 (X = F, Cl, Br) under ambient conditions. ( R -3-XPEA) 2 PbBr 4 (X = F, Cl, Br) crystals were grown by slowly cooling an aqueous HBr solution containing stoichiometric amounts of PbBr 2 and halogen-substituted organic amines, R -3-XPEA (X = F, Cl, Br). The single-crystal XRD results revealed that ( R -3-XPEA) 2 PbBr 4 crystallized in the chiral monoclinic space group P 2 1 under ambient conditions (Supplementary Tables 1–3). As shown in Figs. 1 a– 1 c, inorganic [PbBr 6 ] 4− octahedrons shared vertices to form the Pb–Br layer. Inorganic Pb–Br sheets connected two layers of monovalent R -3-XPEA + cations by Coulombic and hydrogen bonding interactions, forming 2D Ruddlesden–Popper perovskites (Supplementary Figs. 1–3). The inorganic interlayer spacing of the perovskites were in the order of 10.87 Å (( R -3-FPEA) 2 PbBr 4 ) < 11.70 Å (( R -3-ClPEA) 2 PbBr 4 ) < 11.90 Å (( R -3-BrPEA) 2 PbBr 4 ), which was consistent with the atomic size of the meta-substituted halogen in R -3-XPEA + . Simultaneously, halogen···halogen interactions were expected to form in ( R -3-XPEA) 2 PbBr 4 with decreased halogen distances between organic layers. The parameter Δ d x (Δ d x = d x − r x ) was employed to evaluate the halogen···halogen interactions strength, which was defined as the discrepancy between the atomic distance of halogens ( d x ) and the sum of their theoretical van der Waals radii ( r x ). 46 When d x < r x , strong halogen···halogen interactions occurred in ( R -3-XPEA) 2 PbBr 4 . Specifically, owing to the strong electronegativity of F atoms, halogen···halogen interactions were absent in ( R -3-FPEA) 2 PbBr 4 . A Δ d Cl value of 0.09 Å in ( R -3-ClPEA) 2 PbBr 4 was critical for forming Cl···Cl interaction, whereas Δ d Br was − 0.04 Å in ( R -3-BrPEA) 2 PbBr 4 , suggesting that Br···Br interaction was stronger than Cl···Cl interaction. Therefore, the halogen···halogen interactions in ( R -3-XPEA) 2 PbBr 4 became stronger as the atomic number of the meta-substituted halogen in R -3-XPEA + increased. Differentiated halogen···halogen interactions were expected to affect the structural and optical characteristics of ( R -3-XPEA) 2 PbBr 4 . The distance between the primary NH 3 + and the plane of terminal Br defines the penetration depth ( d P ). As the atomic number of the meta-substituted halogen in R -3-XPEA + increased, the d P of R -3-XPEA + into the [PbBr 6 ] 4− octahedral inorganic framework gradually became shallower (Fig. 1 d), which was consistent with the law of enhanced halogen···halogen interactions in ( R -3-XPEA) 2 PbBr 4 . To facilitate a more comprehensive analysis of the relationship between halogen···halogen interactions and structure, the Br–Pb–Br bond angle variance ( δ 2 ) was introduced to quantify the structural distortion of the [PbBr 6 ] 4− octahedron from an ideal octahedral structure. The δ 2 value decreased from ( R -3-FPEA) 2 PbBr 4 to ( R -3-ClPEA) 2 PbBr 4 to ( R -3-BrPEA) 2 PbBr 4 , which was consistent with the order of halogen···halogen interactions strength (Fig. 1 d). The study findings indicated that halogen···halogen interactions may play a role in guiding the [PbBr 6 ] 4− octahedron toward the ideal structure, thereby exerting a substantial influence on the optical properties of ( R -3-XPEA) 2 PbBr 4 . Before discussing the optical features of ( R -3-XPEA) 2 PbBr 4 , we confirmed the crystalline phase purity of the prepared samples by the consistency of the simulated powder XRD patterns of powder samples and single crystals (Supplementary Figs. 4–6). The absorption spectra of ( R -3-XPEA) 2 PbBr 4 were similar, demonstrating an obvious exciton absorption peak at approximately 388 nm (Fig. 1 e). The photoluminescence (PL) spectra of ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 exhibited dual emissions consisting of the FE (399 nm) and STE (520 ~ 560 nm) states. Interestingly, the FE emission peak gradually became sharper from ( R -3-FPEA) 2 PbBr 4 to ( R -3-ClPEA) 2 PbBr 4 to ( R -3-BrPEA) 2 PbBr 4 , which was consistent with the order of halogen···halogen interactions strength. Furthermore, chiral organic ammonium molecules endowed ( R -3-XPEA) 2 PbBr 4 with chiroptical activity. The opposite signals of ( R -3-XPEA) 2 PbBr 4 and ( S -3-XPEA) 2 PbBr 4 in the CPL spectra confirmed that chirality was successfully transferred from R -3-XPEA + to the inorganic Pb–Br sheets (Fig. 1 f). The values of the asymmetry factor ( g lum ) of ( S / R -3-FPEA) 2 PbBr 4 , ( S / R -3-ClPEA) 2 PbBr 4 , and ( S / R -3-BrPEA) 2 PbBr 4 were ± 1.1 × 10 − 2 , ± 3.0 × 10 − 2 , and ± 2.4 × 10 − 2 , respectively (Supplementary Figs. 7–9). In situ high-pressure optical measurement of ( R -3-XPEA) 2 PbBr 4 (X = F, Cl, Br). To further investigate the impact of halogen···halogen interactions on the optical properties of ( R -3-XPEA) 2 PbBr 4 , in situ high-pressure PL and absorption spectroscopy were performed. As shown in Fig. 2 a, STE emission intensity in the low-energy region of ( R -3-ClPEA) 2 PbBr 4 continued to weaken with increased pressure until it disappeared. By contrast, FE emission intensity in the high-energy region continued to increase until 2.5 GPa, with a tenfold increase in intensity. Meanwhile, the peak center of FE emission monotonically redshifted to 412.4 nm, and the full width at half maximum narrowed to 10.4 nm (Supplementary Fig. 10). The PL microphotographs of ( R -3-ClPEA) 2 PbBr 4 crystals during compression exhibited piezochromic luminescence from warm white to deep blue (Fig. 2 b). The evolution process of the emission peak under pressure in ( R -3-BrPEA) 2 PbBr 4 was similar to that in ( R -3-ClPEA) 2 PbBr 4 , and the strongest deep-blue emission was obtained at 1.7 GPa (Supplementary Figs. 11–12). Based on the PL spectra, the corresponding Commission Internationale de l’Eclairage (CIE) color coordinates demonstrated pressure-induced emission color modulation from yellow to deep blue in ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 (Supplementary Figs. 13–14). Notably, the chromaticity coordinates of pressure-induced deep- blue light were (0.17, 0.04), which satisfied the requirement of Rec. 2020 display standards. The PL spectral evolution under compression in ( R -3-FPEA) 2 PbBr 4 , in the absence of halogen···halogen interactions, differed from that in ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 . The emission peak of ( R -3-FPEA) 2 PbBr 4 was governed by broadband STE emission (Figs. 2 b, 2 e and Supplementary Fig. 15). The pressure-dependent PL microphotographs and CIE color coordinates of ( R -3-FPEA) 2 PbBr 4 demonstrated that the emission color gradually changed from yellow to warm white (Fig. 2 d and Supplementary Fig. 16). Conversely, ( R -3-FPEA) 2 PbBr 4 did not emit deep-blue light in the tested pressure range. The in situ high-pressure absorption spectra demonstrated a consistent red shift of band edges with pressure in ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 . The band gap energy, determined by linearly fitting the edge of the absorption curve, exhibited a monotonic decrease with pressure, indicating that the application of hydrostatic pressure adjusted the lattice and atomic distance in ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 (Supplementary Figs. 17–19). Exploring crystal structure evolution under compression is essential to understanding the structure–property relationship between halogen···halogen interactions and FE emission. Thus, pressure-dependent ADXRD and Raman spectroscopy were performed. As shown in Figs. 3 a, 3 b and Supplementary Fig. 20, the diffraction peaks moved toward higher angles with increasing pressure, indicating ongoing lattice contraction in ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 . Additionally, the vibration signals exhibited a blue shift in the in situ high-pressure Raman spectra, providing further evidence of lattice contraction (Supplementary Fig. 21). Importantly, no new signals were observed in the ADXRD and Raman spectra within the tested pressure range, suggesting the absence of structural phase transitions in ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 . Therefore, the pressure-induced deep-blue emission in (R-3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 also expressed CPL activity. Illustration of the compression process and octahedral tilt. Lattice parameter variations with pressure provided insight into lattice shrinkage in ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 induced by anisotropic compression (Figs. 3 c, 3 d, Supplementary Figs. 22–26, and Supplementary Tables 4–6). Specifically, a higher degree of compressibility was observed along the c -axis perpendicular to the inorganic Pb–Br layers. Interlayer compression greatly shortened the distance between inorganic layers, simultaneously decreasing the halogen···halogen distances in adjacent organic layers in ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 (Supplementary Figs. 27–28). The ∆ d Cl value decreased from 0.09 Å at 1 atm to − 0.03 Å at 2.5 GPa, indicating that pressure strengthened Cl···Cl interactions in ( R -3-ClPEA) 2 PbBr 4 (Figs. 4 a and 4 b). Meanwhile, the progressive red shift observed in the C–Cl bond stretching signal (785 cm − 1 ) in the in situ high-pressure IR spectrum provided compelling evidence for enhanced Cl···Cl interaction strength in ( R -3-ClPEA) 2 PbBr 4 (Figs. 3 e and 3 f). 47 Analysis of the noncovalent interaction index provided another qualitative assessment of the enhanced Cl···Cl interaction in ( R -3-ClPEA) 2 PbBr 4 . As depicted in Supplementary Fig. 29, a green isosurface was observed within the ClPEA + ···ClPEA + homodimer, 48 confirming the propensity of organic ammonium layers to establish Cl···Cl interaction at 1 atm and 2.5 GPa. Simultaneously, the Cl–Cl bond energy at 2.5 GPa exceeded that at 1 atm, providing further evidence of pressure-intensified Cl···Cl interaction (Supplementary Fig. 29). Similarly, the ∆ d Br value, which continuously decreased from − 0.04 Å at 1 atm to − 0.14 Å at 1.7 GPa in ( R -3-BrPEA) 2 PbBr 4 , suggested the reinforcement of Br···Br interaction with pressure (Supplementary Fig. 28). The persistent absence of halogen···halogen interactions in ( R -3-FPEA) 2 PbBr 4 was portended by Δ d F > 0 (Figs. 4 e, 4 f, and Supplementary Fig. 28). To further dissect the role of halogen···halogen interactions in the structural evolution of ( R -3-FPEA) 2 PbBr 4 , ( R -3-ClPEA) 2 PbBr 4 , and ( R -3-BrPEA) 2 PbBr 4 , the changes in d P and δ 2 with pressure were explored (Supplementary Fig. 30 and Fig. 2 f). With increasing pressure, interlayer shrinkage enhanced the interactions between organic amine layers, drawing organic amines closer to one another and reducing their penetration depth into the inorganic framework (Figs. 4 g, 4 h and Supplementary Fig. 30). Enhanced Cl···Cl and Br···Br interactions in ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 further drew organic amines away from the inorganic framework, which led to their d P values being shallower than in ( R -3-FPEA) 2 PbBr 4 (Supplementary Fig. 30). As shown in Figs. 4 c and 4 d, the enhanced halogen···halogen interactions guided the tilt and movement of the [PbBr 6 ] 4− octahedron with pressure. During compression, the δ 2 values of ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 substantially decreased as Cl···Cl and Br···Br interactions were reinforced, reaching minimum values at 2.5 and 1.7 GPa, respectively (Fig. 2 f). This finding corresponded to the pressures at which the strongest deep-blue CPL was observed in the PL spectra of ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 . When halogen···halogen interactions were absent, the δ 2 value slightly decreased and then rapidly increased in ( R -3-FPEA) 2 PbBr 4 , hindering deep-blue emission (Fig. 2 f). Therefore, pressure-induced enhancement of halogen···halogen interactions substantially reduced the penetration depth of organic amines, effectively mitigating structural distortion of the inorganic Pb–Br layer. Density functional theory (DFT) calculations. To clarify the photophysical mechanism underlying pressure-triggered deep-blue emission in ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 , DFT calculations of the electronic band structure and partial density of states of ( R -3-ClPEA) 2 PbBr 4 were performed. As shown in Supplementary Fig. 31, the valence band maximum of ( R -3-ClPEA) 2 PbBr 4 was primarily attributed to the Br 4p and Pb 6s orbitals, while the conduction band minimum predominantly consisted of the Pb 6p orbitals. The organic component, acting as an electron barrier, did not contribute to the electronic states at the band edge due to its density of states being projected at a deeper energy level. 49 Therefore, the results indicated that the photophysical property evolution in ( R -3-XPEA) 2 PbBr 4 was governed by the [PbBr 6 ] 4− octahedral structure. The reduction in band gap energy at 2.5 GPa was attributed to enhanced orbital overlap due to the shortened Pb–Br bond length (Supplementary Fig. 32). The progressive decrease in the band gap energy under pressure in ( R -3-XPEA) 2 PbBr 4 was consistent with the continuous shortening of the Pb–Br bond length (Supplementary Figs. 33–35). Theoretical analysis of excited states further suggested that pressure-induced deep-blue emission could be attributed to the facilitated de-trapping of the STE state, which was facilitated by the reduced transient elastic deformation within the inorganic lattice. The excited states involved in electron–phonon coupling at 1 atm and 2.5 GPa are depicted in Figs. 5 a and 5 b, respectively. The strong electron–phonon coupling effect created by the distorted lattice at 1 atm effectively captured and confined excitons within the lattice, resulting in the localization of electrons and holes within a specific inorganic [PbBr 6 ] 4− octahedron. By contrast, the diminished lattice distortion induced by increased Cl···Cl interaction at 2.5 GPa impeded electron–phonon coupling, facilitating the unrestricted movement of electrons and holes within the lattice. The configuration coordinate diagrams of STE formation at 1 atm and 2.5 GPa are presented in Figs. 5 c and 5 d, respectively. ΔE st denotes the self-trapping depth, which refers to the difference between the STE and FE configurations in the excited state. High STE emission is frequently observed at greater self-trapping depths. 50 The calculated self-trapping depth at 1 atm (0.120 eV) surpassed that at 2.5 GPa (0.007 eV), suggesting a higher likelihood of STE radiative recombination at 1 atm than at 2.5 GPa. Therefore, ( R -3-ClPEA) 2 PbBr 4 crystals exhibited warm-white luminescence dominated by broadband STE emission at 1 atm (Fig. 5 e) and deep-blue luminescence led by narrow-band FE emission at 2.5 GPa (Fig. 5 f). The Huang–Rhys factor ( S ) was employed to quantitatively describe electron–phonon coupling strength, thereby facilitating a deeper understanding of the mechanism underlying pressure-induced deep-blue emission. The S value is estimated by ΔE stokes = 2 Sћ ω LO , where E stokes represents the Stokes shift energy and ω LO represents the vibration energy of the longitudinal optical phonon. 51 The considerable decrease in S value with increasing pressure in ( R -3-ClPEA) 2 PbBr 4 provided further evidence of effective suppression of the electron–phonon coupling effect through pressure-induced Cl···Cl interaction enhancement (Supplementary Fig. 36). The S value of ( R -3-FPEA) 2 PbBr 4 far exceeded that of ( R -3-ClPEA) 2 PbBr 4 , indicating that ( R -3-FPEA) 2 PbBr 4 tended to exhibit broadband STE emission due to stronger electron–phonon coupling in the absence of halogen···halogen interactions (Supplementary Fig. 37). The evolution of S values with pressure in ( R -3-BrPEA) 2 PbBr 4 was similar to that in ( R -3-ClPEA) 2 PbBr 4 (Supplementary Fig. 38), demonstrating a sharp decrease in S values with increasing pressure. This finding suggested that the enhancement of Cl···Cl and Br···Br interactions facilitated the de-trapping of the STE state back to the FE state by weakening electron–phonon coupling. Furthermore, the short lifetime components in the STE emission lifetime of ( R -3-ClPEA) 2 PbBr 4 increased with pressure, further signifying that the STE state gradually de-trapped back to the FE state under compression (Supplementary Fig. 39 and Supplementary Table 7). Conclusion In this work, we successfully synthesized novel 2D chiral perovskites, ( R -3-XPEA) 2 PbBr 4 , with discrepancies in halogen···halogen interactions by employing halogen-substituted chiral organic amine and PbBr 2 . Pressure-driven enhancement of halogen···halogen interactions in ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 achieved high color–purity deep-blue CPL controlled by narrow-band FE emission under moderate pressure. Without halogen···halogen interactions, ( R -3-FPEA) 2 PbBr 4 exhibited yellow light commanded by broadband STE emission under high pressure. The ADXRD and DFT results demonstrated that halogen···halogen interactions played a crucial role in guiding the tilt and movement of the inorganic [PbBr 6 ] 4− octahedron under high pressure. Greatly diminished lattice distortion originating from reinforced halogen···halogen interactions weakened electron–phonon coupling, facilitating FE radiative recombination to realize deep-blue CPL in ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 . By contrast, ( R -3-FPEA) 2 PbBr 4 , without halogen···halogen interactions, was unable to achieve blue emission owing to the inability to prevent structural distortion. Methods Synthesis of ( R -3-XPEA) 2 PbBr 4 (PEA = phenethylamine, X = F, Cl, Br). PbO (0.5 mmol) was dissolved in a mixed solution of 2 mL of concentrated aqueous HBr and 0.5 mL of concentrated aqueous H 3 PO 3 under heating and vigorous stirring until a clear solution was obtained. The temperature of the hot plate was set to 120 o C to keep the HBr solution boiling. The R -3-XPEA (1 mmol) was added to 0.5 mL of concentrated aqueous HBr solution in a separate vial under stirring. The neutralized R -3-XPEA solution was added to the boiling HBr solution under vigorous stirring. Then the temperature was lowered to 100 o C until colorless plate-shaped crystals started to precipitate out. Further decrease of the temperature to 60 o C resulted in precipitation of most of the crystals within 1h. Then the hot plate was turned off, and the solution was cooled slowly to room temperature. Crystallographic data collection and refinement of the structure. Single-crystal X-ray diffraction analysis (SCXRD). SCXRD measurements of ( R -3-ClPEA) 2 PbBr 4 and ( R -3-BrPEA) 2 PbBr 4 were performed on a Bruker D8 VENTURE diffractometer with Mo-K α radiation (λ = 0.71073 Å). Data reduction was performed using the APEX3 software package. SCXRD measurement of ( R -3-FPEA) 2 PbBr 4 was performed on a Rigaku XtaLAB Pro diffractometer with Cu-K α radiation ( λ = 1.54184 Å). Data collection and reduction were performed using the program CrysAlis Pro . The three structures were all assessed with direct methods (SHELXS) 52 and refined by full-matrix least squares in F2 using OLEX2, 53 which utilizes the SHELXL-2015 module. 54 The crystal structures were visualized in DIAMOND 3.2. 55 Detailed information about the X-ray crystal data, intensity collection procedure and refinement results for ( R -3-XPEA) 2 PbBr 4 (X = F, Cl, Br) are summarized in Supplementary Tables 1–6. Powder X-ray diffraction (PXRD) . PXRD patterns of the ( R -3-XPEA) 2 PbBr 4 samples were recorded on a D/MAX-3D diffractometer (Cu Kα, λ = 1.54178 Å). Simulated powder patterns were obtained with Mercury software and a crystallographic information file (CIF) from a single-crystal X-ray experiment. Circularly polarized luminescence (CPL). CPL spectra were obtained by a JASCO CPL-300 spectropolarimeter in the solid state. Each CPL spectrum was the average of at least three scans. The degree of chirality can be quantified by the anisotropy factor g lum , which is defined as g lum = 2(I L − I R )/(I L + I R ), where I L and I R represent the photoluminescence intensity of left- and right-circularly polarized light respectively. 56 Analysis of octahedral distortion. The degree of octahedral distortion was determined by using the parameter δ 2 , \(\:{\delta\:}^{2}=\frac{1}{11}\sum\:_{i=1}^{12}{\left(\text{θ}\text{i}-\text{90}\right)}^{2}\) , where θ i represents the individual Br-Pb-Br bond angles of the octahedron. 57 High-pressure Generation. High-pressure experiments were carried out with a symmetric-type diamond-anvil cell (DAC) with a pair of 300 µm culets. The sample and a small ruby ball were loaded into the 150 µm-diameter chamber of a DAC, constructed from a T301 steel gasket pre-indented to a thickness of 45 µm. In high-pressure experiments, silicon oil was utilized as the pressure transmitting medium (PTM) for optical absorption, PL, TRPL, Raman and ADXRD experiments. The PTM did not have any detectable effect on the behavior of ( R -3-XPEA) 2 PbBr 4 under pressure. All of the measurements were performed at room temperature. In situ high-pressure optical measurements. PL spectra were measured by using a 360 nm laser excitation. Absorption spectra were measured by using a deuterium-halogen light source (Ocean Insight DH-2000-BAL) and a fiber spectrometer of Ocean Insight QEP03490. PL and optical micrographs of the samples were obtained using a camera (Olympus DP74) equipped with a microscope (Olympus BX53). The camera can record the photographs under the same conditions including exposure time and intensity. Raman spectra were collected in a MonoVista CRS + spectrometer with a 532 nm laser excitation. The TRPL spectra were performed using a homemade spectroscopy system (Ideaoptics, Shanghai, China) with a 375 nm laser as the excitation source. The measured PL decay curves were fitted using double exponential functions I(t) = I(0) × [A 1 × exp(-t/τ 1 ) + A 2 × exp(-t/τ 2 )]. We performed in situ high-pressure ADXRD measurements with the wavelength of 0.6199 Å at the 4W2 beamline at the High-Pressure Station of the Beijing Synchrotron Radiation Facility. We used CeO 2 as a standard sample to do the calibration. The 2D Debye-Scherrer diffraction rings were recorded using an imaging plate detector and integrated into the 1D profile using the Dioptas program. All high-pressure experiments were conducted at room temperature. Computational Details. Density functional theory (DFT) calculations are performed using the plane-wave pseudopotential as implemented in the Vienna Ab-initio Simulation Package (VASP). 58 – 59 The electron-core interactions are described with the frozen-core projector-augmented wave pseudopotentials. 60 The generalized gradient approximation formulated by Perdew, Burke, and Ernzerhof (PBE) as the exchange-correlation functional with cutoff energies of 520 eV was chosen in all of the calculations. 61 The total energy convergence criteria is 1.0 × 10 − 5 eV and the force on each atom converges to 0.01 eV Å −1 in optimizing the geometric structure. The vdW interaction is considered by using the DFT-D3 method of Grimme. 62 Pressure values are calculated through the relation P = -∂E/∂V, where E is the energy of the crystal and V is the cell volume. The spin-orbit coupling (SOC) effect is important in cubic lead halide perovskites. We test the band gap of the 2D lead bromide perovskite ( R -3-ClPEA) 2 PbBr 4 . The PBE calculated band gap energy is 2.79 eV. The without and with HSE06 calculated band gaps are 3.56 eV and 2.86 eV, respectively. Thus, the PBE is only 0.29 eV smaller than the experiment band gap of 3.08 eV. The reason for 2D and 1D lead halide perovskites, the SOC is significantly quenched due to the crystal field splitting of the Pb 6 p orbitals. Since the SOC induced effective mass change is also minor in 2D perovskites, the effect on the self-trapping is expected to be small. 63 Therefore, we neglect the SOC effect on the STE calculations. To study the STE properties, a 2×2×1 supercell containing 376 atoms with Γ only k point is used in the calculations. The excited states were achieved by the constrained occupancy method. The triplet STE state was achieved by setting the spin quantum number. Following Wang et al. 63 , the configurational coordinate diagrams were constructed by linear interpolating the coordinates between the ground and STE configurations then the total energies both of the ground and excited STE state at each coordinate can be got. The coordinate difference between the ground and STE is \(\:\varDelta\:\text{Q}=\sqrt{{\sum\:}_{k,i}{m}_{k}({R}_{k,i}^{e}-{R}_{k,i}^{g})}\) , where k labels the atoms, i = (x, y, z), m is the atomic mass, and R is the atomic coordinates with e and g for the excited and ground state, respectively. Note that the underestimated 0.29 eV band gap arising from DFT-PBE compared with the experiment value was corrected with the scissor method in the configurational coordinate diagrams. Theoretical calculation of weak interaction calculations. The initial step involved extracting the dimeric structure from the crystal lattice. Subsequently, we performed structural optimization and vibrational analysis, concentrating on the hydrogen atom. Utilizing the Gaussian 16 software package, 64 we employed the B3LYP functional 65 – 66 and D3BJ dispersion correction 62 for tasks such as structural optimization and vibration analysis. The optimized molecular structures and vibration analysis were determined using the 6-31G* basis set. 67 – 68 For weak interaction calculations, we utilized the M06-2X functional 69 and the ma-def2-TZVP basis sets 70 . Additionally, a thorough analysis of weak interactions was carried out using the Interaction Region Indicator (IRI) 48 with Multiwfn 3.8 71 . To visualize the system's structure and weak interactions, we employed VMD 72 . Declarations Data availability. Data supporting the findings of this manuscript are available from the corresponding authors upon reasonable request. The X-ray crystallographic coordinates for structures reported in this article have been deposited at the Cambridge Crystallographic Data Centre (CCDC) under deposition numbers CCDC: 2327085 ( ( R -3-FPEA) 2 PbBr 4 ), 2327086 ( ( R -3-ClPEA) 2 PbBr 4 ), and 2327087 ( ( R -3-BrPEA) 2 PbBr 4 ). Acknowledgments This work was supported by the National Key R&D Program of China (2021YFA1200301), the National Natural Science Foundation of China (nos. 92061201, 21825106, 52103238), Zhongyuan Thousand Talents (Zhongyuan Scholars) Program of Henan Province (234000510007), the China Postdoctoral Science Foundation (nos. 2021TQ0289, 2021M700128, 2023T160197 and 2022M711061), and Zhengzhou University. The in situ high-pressure powder XRD was performed at 4W2 HP-Station in the Beijing Synchrotron Radiation Facility (BSRF) and BL15U1 Station in the Shanghai Synchrotron Radiation Facility (SSRF). Author contributions † M.-E. Sun, F. Wang and M. He contributed equally to this work. S.-Q. Zang, Y. Wu and G. Chen supervised the project. M.-E. Sun, Y.-N. Yang, J.-K. Yang, and X.-J Zhang synthesized the crystals and characterized the material properties in high-pressure. F. Wang carried out first principles DFT calculations. Y. Wang, Y. Fu and Q. Li revised the manuscript. J. Lei and Z. Wang participated in discussions and gave much helpful suggestion. M.-E. Sun, M. He and G. Chen wrote the paper, and all the authors read and commented on the paper. Additional information Supplementary information is available in the online version of the paper. Reprints and permissions information is available online at www.nature.com/reprints. 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Chem. 33 , 580-592 (2012). Humphrey W., Dalke A. & Schulten K., VMD: Visual molecular dynamics. J. Mol. Graphics 14 , 33-38 (1996). Additional Declarations There is NO Competing Interest. Supplementary Files R3BrPEA2PbBr4.cif R3ClPEA2PbBr4.cif R3FPEA2PbBr4.cif CheckcifR3BrPEA2PbBr4.pdf CheckcifR3ClPEA2PbBr4.pdf CheckcifR3FPEA2PbBr4.pdf SupportingInformation.doc Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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(\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-3-XPEA)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e under ambient conditions. \u003c/strong\u003ea–c) Schematic single-crystal structures of a) (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, b) (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and c) (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. d) Penetration depth (\u003cem\u003ed\u003c/em\u003e\u003csub\u003eP\u003c/sub\u003e) of \u003cem\u003eR\u003c/em\u003e-3-XPEA\u003csup\u003e+\u003c/sup\u003e into the Pb–Br inorganic framework and variance (\u003cem\u003eδ\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e) of the Br–Pb–Br bond angle in the [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4−\u003c/sup\u003e octahedron. The inset shows \u003cem\u003ed\u003c/em\u003e\u003csub\u003eP\u003c/sub\u003e, which is defined by the distance between the primary NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e and the plane of terminal bromines. e) Optical absorption and photoluminescence (PL) spectra of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. f) Circularly polarized luminescence (CPL) spectra of (\u003cem\u003eS\u003c/em\u003e/\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eS\u003c/em\u003e/\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eS\u003c/em\u003e/\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4687727/v1/8056905eda908dc7043bae6d.png"},{"id":60559485,"identity":"97b463b5-b0dd-492b-a956-54e94e11a4a8","added_by":"auto","created_at":"2024-07-18 07:14:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":662204,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSpectroscopic measurements and microphotographs of (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-3-ClPEA)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e and (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-3-FPEA)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e under high pressure. \u003c/strong\u003ea, b) In situ pressure-dependent photoluminescence spectra of a) (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and b) (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. c, d) Microphotographs in the sample chamber at selected pressures under the ultraviolet field for c) (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and d) (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. e) Intensity ratio of FE and STE emissions (I\u003csub\u003eFE\u003c/sub\u003e/I\u003csub\u003eSTE\u003c/sub\u003e) of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e at different pressures. f) Variations in bond angle variance (\u003cem\u003eδ\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e) in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e under pressure.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4687727/v1/19b698a56692411346a2e503.png"},{"id":60559479,"identity":"0b63d83b-4af5-4dd6-9a55-f4b46b7b62d1","added_by":"auto","created_at":"2024-07-18 07:14:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":449778,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIn situ structural characterization of (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-3-FPEA)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e and (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-3-ClPEA)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e under high pressure. \u003c/strong\u003ea, b) Angle-dispersive X-ray diffraction patterns of a) (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and b) (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e at selected pressures. c, d) Pressure-dependent lattice parameters of c) (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and d) (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. e) In situ high-pressure infrared (IR) spectra of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. f) Frequency variation of C–Cl stretching modes with applied pressure.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4687727/v1/c20c2a89a4dbe287345d86bc.png"},{"id":60559490,"identity":"203fcbc4-3bbb-4c2e-8249-70dc71cf3931","added_by":"auto","created_at":"2024-07-18 07:14:26","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":452174,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIllustration of the compression process of (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-3-ClPEA)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e and (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-3-FPEA)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e. \u003c/strong\u003ea-b) Crystal structure models of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e under a) 1 atm and b) 2.5 GPa. c-d) The mechanism of structural evolution in inorganic [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4-\u003c/sup\u003e octahedron guided by pressure-enhanced halogen···halogen interactions at c) 1 atm and d) 2.5 GPa. e-f) Crystal structure models of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e under e) 1 atm and f) 2.3 GPa. g-h) The mechanism of structural evolution in inorganic [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4-\u003c/sup\u003e octahedron under pressure at g) 1 atm and h) 2.3 GPa.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4687727/v1/3b00806f8c79f001d69def82.png"},{"id":60560303,"identity":"e658f628-9d35-4f27-a25c-a4239c5d5c2d","added_by":"auto","created_at":"2024-07-18 07:22:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":507976,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTheoretical studies of pressure-induced deep-blue emission in (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-3-ClPEA)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003ePbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e. \u003c/strong\u003ea-b) The electronic charge densities for the valence band maximum (VBM) and conduction band minimum (CBM) for (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e supercells at a) 1 atm and b) 2.5 GPa. c-d) One-dimensional configuration coordinate diagram of the ground, excited, and STE states for (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e at c) 1 atm and d) 2.5 GPa. The ΔE\u003csub\u003est\u003c/sub\u003e is the self-trapping energy. e-f) Configuration coordinate diagram for the (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e at e) 1 atm and f) 2.5 GPa. FE, free exciton state; GS, ground state; STE, self-trapped state.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4687727/v1/97886116b8a48a0858e86580.png"},{"id":72010887,"identity":"ed6d64c1-0e9f-4db3-8bd1-9d44d91a8a41","added_by":"auto","created_at":"2024-12-20 15:08:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3716905,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4687727/v1/afedae72-3a4f-4414-915f-4897e15cb579.pdf"},{"id":60559494,"identity":"b56b3361-a4b7-4796-b377-72bced590bcc","added_by":"auto","created_at":"2024-07-18 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07:14:26","extension":"doc","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":6551040,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"SupportingInformation.doc","url":"https://assets-eu.researchsquare.com/files/rs-4687727/v1/b2c5c56139c54ca921410e27.doc"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Halogen-Dependent Deep-Blue Circularly Polarized Emitters with Ultrahigh-Color-Purity Under High Pressure","fulltext":[{"header":"Introduction","content":"\u003cp\u003eLow-dimensional (2D, 1D, and 0D) metal halide perovskites (LDMHPs) have attracted considerable research attention for light-emitting diodes, nonlinear photonics, and detectors owing to their large exciton binding energy, diverse structures, and quantum confinement effects.\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e LDMHPs can be prepared by replacing cesium (Cs\u003csup\u003e+\u003c/sup\u003e), formamidine (FA\u003csup\u003e+\u003c/sup\u003e), or methylammonium (MA\u003csup\u003e+\u003c/sup\u003e) in 3D metal halide perovskites with larger organic amine cations.\u003csup\u003e\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e Bulky ammoniums exacerbate the structural distortion of the metal halide octahedron and induce a strong electron\u0026ndash;phonon coupling effect in LDMHPs,\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e facilitating trapping of the free exction (FE) state by the distorted lattice and transformation into the self-trapped exciton (STE) state.\u003csup\u003e\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e Thus, FE radiative recombination is the dominant process in 3D perovskites; however, it is scarce in LDMHPs. In contrast to broadband STE emission, radiative recombination results in narrower-band FE emission and higher luminescence color purity. FE-dominated luminescent materials are promising candidates for micro-nano lasers and highly sensitive sensors.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e Effectively suppressing the large structural distortion and strong electron\u0026ndash;phonon coupling effect in LDMHPs is expected to achieve FE emission and help to expand their applications.\u003c/p\u003e \u003cp\u003eQuantum and dielectric confinement effects are often employed to tune FE emission characteristics in perovskites.\u003csup\u003e\u003cspan additionalcitationids=\"CR18 CR19\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e However, the key role of noncovalent interactions (i.e., hydrogen bonding and halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions) is frequently ignored in the regulation of perovskite FE emission behavior. Halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions, as a novel form of noncovalent interactions, have garnered growing interest among researchers due to their powerful ability to manipulate chiroptical activity, nonlinear optical response, and photoelectric conversion efficiency.\u003csup\u003e\u003cspan additionalcitationids=\"CR22 CR23 CR24\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e The ability of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions to control the structure and optical properties of materials makes it a potential strategy for FE emission manipulation in perovskites. Nevertheless, the inability to continuously and controllably regulate halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions severely restricts their use in managing the FE emission behavior of LDMHPs. Therefore, convenient and efficient strategies based on halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions are urgently needed to regulate the FE emission behavior of LDMHPs and systematically elucidate the intrinsic mechanism of noncovalent interactions driving FE emission.\u003c/p\u003e \u003cp\u003eHydrostatic pressure can be utilized as a powerful tool to efficiently manipulate the crystal and electronic structures and physicochemical properties of materials by shortening interatomic distances and increasing orbital overlap.\u003csup\u003e\u003cspan additionalcitationids=\"CR27 CR28 CR29 CR30 CR31 CR32 CR33 CR34 CR35\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e Currently, strengthening noncovalent interactions via the hydrostatic pressure effect is utilized to enhance luminescence, improve conductivity, narrow the band gap, and optimize chiroptical activity in perovskites, metal\u0026ndash;organic frameworks, and organic molecules.\u003csup\u003e\u003cspan additionalcitationids=\"CR38 CR39 CR40 CR41 CR42 CR43 CR44\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e Thus, applying hydrostatic pressure to LDMHPs is expected to achieve FE emission through pressure-enhanced halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions, thereby clarifying the structure\u0026ndash;property relationship between structural distortion, noncovalent interactions, and FE emission behavior.\u003c/p\u003e \u003cp\u003eHerein, three novel 2D chiral organic\u0026ndash;inorganic halide perovskites (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (PEA\u0026thinsp;=\u0026thinsp;phenethylamine, X\u0026thinsp;=\u0026thinsp;F, Cl, Br) with different halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions were successfully prepared. Under ambient conditions, (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals presented broadband yellow circularly polarized luminescence (CPL) dominated by STE emission. Variations in halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions strength generated discrepancies in the pressure-dependent CPL spectral evolution of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. With increased pressure, (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals exhibited remarkable piezochromic luminescence from yellow to cold-white to deep-blue. (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e exhibited narrow-band deep-blue (λ\u0026thinsp;\u0026lt;\u0026thinsp;450 nm) CPL at pressures of 1.7 and 2.5 GPa, respectively. However, deep-blue CPL prevailed by FE states is absent in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. The in situ high-pressure angle-dispersive X-ray diffraction (ADXRD) results indicated that pressure weakened the penetration depths of \u003cem\u003eR\u003c/em\u003e-3-BrPEA\u003csup\u003e+\u003c/sup\u003e and \u003cem\u003eR\u003c/em\u003e-3-ClPEA\u003csup\u003e+\u003c/sup\u003e into the [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedral frameworks by strengthening halogen\u0026middot;\u0026middot;\u0026middot;halogen (Br\u0026middot;\u0026middot;\u0026middot;Br and Cl\u0026middot;\u0026middot;\u0026middot;Cl) interactions between adjacent organic amines, which drove [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e to approach an ideal octahedral structure by suppressing the structural distortion of the inorganic sublattice. Density functional theory (DFT) calculations further demonstrated that reducing structural distortion weakened the electron\u0026ndash;phonon coupling effect, promoting the de-trapping of the STE state back to the FE state. Conversely, structural distortion failed to be effectively prevented in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, which lacked halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions, resulting in broadband STE emission. Our findings shed light on the intricate correlations between halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions, structural distortion, and CPL performance in LDMHPs. Meanwhile, our work also provides a novel approach and experimental reference for the preparation of new deep-blue CPL materials with ultrahigh-color-purity.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e \u003cb\u003eSynthesis and characterization of (\u003c/b\u003e \u003cb\u003eR\u003c/b\u003e \u003cb\u003e-3-XPEA)\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003ePbBr\u003c/b\u003e \u003csub\u003e \u003cb\u003e4\u003c/b\u003e \u003c/sub\u003e \u003cb\u003e(X\u0026thinsp;=\u0026thinsp;F, Cl, Br) under ambient conditions.\u003c/b\u003e (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (X\u0026thinsp;=\u0026thinsp;F, Cl, Br) crystals were grown by slowly cooling an aqueous HBr solution containing stoichiometric amounts of PbBr\u003csub\u003e2\u003c/sub\u003e and halogen-substituted organic amines, \u003cem\u003eR\u003c/em\u003e-3-XPEA (X\u0026thinsp;=\u0026thinsp;F, Cl, Br). The single-crystal XRD results revealed that (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystallized in the chiral monoclinic space group \u003cem\u003eP\u003c/em\u003e2\u003csub\u003e1\u003c/sub\u003e under ambient conditions (Supplementary Tables\u0026nbsp;1\u0026ndash;3). As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea\u0026ndash;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec, inorganic [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedrons shared vertices to form the Pb\u0026ndash;Br layer. Inorganic Pb\u0026ndash;Br sheets connected two layers of monovalent \u003cem\u003eR\u003c/em\u003e-3-XPEA\u003csup\u003e+\u003c/sup\u003e cations by Coulombic and hydrogen bonding interactions, forming 2D Ruddlesden\u0026ndash;Popper perovskites (Supplementary Figs.\u0026nbsp;1\u0026ndash;3). The inorganic interlayer spacing of the perovskites were in the order of 10.87 \u0026Aring; ((\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e)\u0026thinsp;\u0026lt;\u0026thinsp;11.70 \u0026Aring; ((\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e)\u0026thinsp;\u0026lt;\u0026thinsp;11.90 \u0026Aring; ((\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e), which was consistent with the atomic size of the meta-substituted halogen in \u003cem\u003eR\u003c/em\u003e-3-XPEA\u003csup\u003e+\u003c/sup\u003e. Simultaneously, halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions were expected to form in (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e with decreased halogen distances between organic layers. The parameter Δ\u003cem\u003ed\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e (Δ\u003cem\u003ed\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e = \u003cem\u003ed\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e \u0026minus; \u003cem\u003er\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e) was employed to evaluate the halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions strength, which was defined as the discrepancy between the atomic distance of halogens (\u003cem\u003ed\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e) and the sum of their theoretical van der Waals radii (\u003cem\u003er\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e).\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e When \u003cem\u003ed\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e \u0026lt; \u003cem\u003er\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e, strong halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions occurred in (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. Specifically, owing to the strong electronegativity of F atoms, halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions were absent in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. A Δ\u003cem\u003ed\u003c/em\u003e\u003csub\u003eCl\u003c/sub\u003e value of 0.09 \u0026Aring; in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was critical for forming Cl\u0026middot;\u0026middot;\u0026middot;Cl interaction, whereas Δ\u003cem\u003ed\u003c/em\u003e\u003csub\u003eBr\u003c/sub\u003e was \u0026minus;\u0026thinsp;0.04 \u0026Aring; in (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, suggesting that Br\u0026middot;\u0026middot;\u0026middot;Br interaction was stronger than Cl\u0026middot;\u0026middot;\u0026middot;Cl interaction. Therefore, the halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions in (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e became stronger as the atomic number of the meta-substituted halogen in \u003cem\u003eR\u003c/em\u003e-3-XPEA\u003csup\u003e+\u003c/sup\u003e increased. Differentiated halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions were expected to affect the structural and optical characteristics of (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThe distance between the primary NH\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e and the plane of terminal Br defines the penetration depth (\u003cem\u003ed\u003c/em\u003e\u003csub\u003eP\u003c/sub\u003e). As the atomic number of the meta-substituted halogen in \u003cem\u003eR\u003c/em\u003e-3-XPEA\u003csup\u003e+\u003c/sup\u003e increased, the \u003cem\u003ed\u003c/em\u003e\u003csub\u003eP\u003c/sub\u003e of \u003cem\u003eR\u003c/em\u003e-3-XPEA\u003csup\u003e+\u003c/sup\u003e into the [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedral inorganic framework gradually became shallower (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed), which was consistent with the law of enhanced halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions in (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. To facilitate a more comprehensive analysis of the relationship between halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions and structure, the Br\u0026ndash;Pb\u0026ndash;Br bond angle variance (\u003cem\u003eδ\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) was introduced to quantify the structural distortion of the [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedron from an ideal octahedral structure. The \u003cem\u003eδ\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e value decreased from (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e to (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e to (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, which was consistent with the order of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions strength (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). The study findings indicated that halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions may play a role in guiding the [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedron toward the ideal structure, thereby exerting a substantial influence on the optical properties of (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eBefore discussing the optical features of (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, we confirmed the crystalline phase purity of the prepared samples by the consistency of the simulated powder XRD patterns of powder samples and single crystals (Supplementary Figs.\u0026nbsp;4\u0026ndash;6). The absorption spectra of (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e were similar, demonstrating an obvious exciton absorption peak at approximately 388 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). The photoluminescence (PL) spectra of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e exhibited dual emissions consisting of the FE (399 nm) and STE (520\u0026thinsp;~\u0026thinsp;560 nm) states. Interestingly, the FE emission peak gradually became sharper from (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e to (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e to (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, which was consistent with the order of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions strength. Furthermore, chiral organic ammonium molecules endowed (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e with chiroptical activity. The opposite signals of (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eS\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e in the CPL spectra confirmed that chirality was successfully transferred from \u003cem\u003eR\u003c/em\u003e-3-XPEA\u003csup\u003e+\u003c/sup\u003e to the inorganic Pb\u0026ndash;Br sheets (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef). The values of the asymmetry factor (\u003cem\u003eg\u003c/em\u003e\u003csub\u003elum\u003c/sub\u003e) of (\u003cem\u003eS\u003c/em\u003e/\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eS\u003c/em\u003e/\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eS\u003c/em\u003e/\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e were \u0026plusmn;\u0026thinsp;1.1 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, \u0026plusmn;\u0026thinsp;3.0 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, and \u0026plusmn;\u0026thinsp;2.4 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively (Supplementary Figs.\u0026nbsp;7\u0026ndash;9).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eIn situ high-pressure optical measurement of (\u003c/b\u003e \u003cb\u003eR\u003c/b\u003e \u003cb\u003e-3-XPEA)\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003ePbBr\u003c/b\u003e \u003csub\u003e \u003cb\u003e4\u003c/b\u003e \u003c/sub\u003e \u003cb\u003e(X\u0026thinsp;=\u0026thinsp;F, Cl, Br).\u003c/b\u003e To further investigate the impact of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions on the optical properties of (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, in situ high-pressure PL and absorption spectroscopy were performed. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, STE emission intensity in the low-energy region of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e continued to weaken with increased pressure until it disappeared. By contrast, FE emission intensity in the high-energy region continued to increase until 2.5 GPa, with a tenfold increase in intensity. Meanwhile, the peak center of FE emission monotonically redshifted to 412.4 nm, and the full width at half maximum narrowed to 10.4 nm (Supplementary Fig.\u0026nbsp;10). The PL microphotographs of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals during compression exhibited piezochromic luminescence from warm white to deep blue (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). The evolution process of the emission peak under pressure in (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was similar to that in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and the strongest deep-blue emission was obtained at 1.7 GPa (Supplementary Figs.\u0026nbsp;11\u0026ndash;12). Based on the PL spectra, the corresponding Commission Internationale de l\u0026rsquo;Eclairage (CIE) color coordinates demonstrated pressure-induced emission color modulation from yellow to deep blue in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (Supplementary Figs.\u0026nbsp;13\u0026ndash;14). Notably, the chromaticity coordinates of pressure-induced deep- blue light were (0.17, 0.04), which satisfied the requirement of Rec. 2020 display standards.\u003c/p\u003e \u003cp\u003eThe PL spectral evolution under compression in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, in the absence of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions, differed from that in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. The emission peak of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was governed by broadband STE emission (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee and Supplementary Fig.\u0026nbsp;15). The pressure-dependent PL microphotographs and CIE color coordinates of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e demonstrated that the emission color gradually changed from yellow to warm white (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed and Supplementary Fig.\u0026nbsp;16). Conversely, (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e did not emit deep-blue light in the tested pressure range. The in situ high-pressure absorption spectra demonstrated a consistent red shift of band edges with pressure in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. The band gap energy, determined by linearly fitting the edge of the absorption curve, exhibited a monotonic decrease with pressure, indicating that the application of hydrostatic pressure adjusted the lattice and atomic distance in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (Supplementary Figs.\u0026nbsp;17\u0026ndash;19).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eExploring crystal structure evolution under compression is essential to understanding the structure\u0026ndash;property relationship between halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions and FE emission. Thus, pressure-dependent ADXRD and Raman spectroscopy were performed. As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;20, the diffraction peaks moved toward higher angles with increasing pressure, indicating ongoing lattice contraction in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. Additionally, the vibration signals exhibited a blue shift in the in situ high-pressure Raman spectra, providing further evidence of lattice contraction (Supplementary Fig.\u0026nbsp;21). Importantly, no new signals were observed in the ADXRD and Raman spectra within the tested pressure range, suggesting the absence of structural phase transitions in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. Therefore, the pressure-induced deep-blue emission in (R-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e also expressed CPL activity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eIllustration of the compression process and octahedral tilt.\u003c/b\u003e Lattice parameter variations with pressure provided insight into lattice shrinkage in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e induced by anisotropic compression (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, Supplementary Figs.\u0026nbsp;22\u0026ndash;26, and Supplementary Tables\u0026nbsp;4\u0026ndash;6). Specifically, a higher degree of compressibility was observed along the \u003cem\u003ec\u003c/em\u003e-axis perpendicular to the inorganic Pb\u0026ndash;Br layers. Interlayer compression greatly shortened the distance between inorganic layers, simultaneously decreasing the halogen\u0026middot;\u0026middot;\u0026middot;halogen distances in adjacent organic layers in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (Supplementary Figs.\u0026nbsp;27\u0026ndash;28). The ∆\u003cem\u003ed\u003c/em\u003e\u003csub\u003eCl\u003c/sub\u003e value decreased from 0.09 \u0026Aring; at 1 atm to \u0026minus;\u0026thinsp;0.03 \u0026Aring; at 2.5 GPa, indicating that pressure strengthened Cl\u0026middot;\u0026middot;\u0026middot;Cl interactions in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Meanwhile, the progressive red shift observed in the C\u0026ndash;Cl bond stretching signal (785 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in the in situ high-pressure IR spectrum provided compelling evidence for enhanced Cl\u0026middot;\u0026middot;\u0026middot;Cl interaction strength in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef).\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAnalysis of the noncovalent interaction index provided another qualitative assessment of the enhanced Cl\u0026middot;\u0026middot;\u0026middot;Cl interaction in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. As depicted in Supplementary Fig.\u0026nbsp;29, a green isosurface was observed within the ClPEA\u003csup\u003e+\u003c/sup\u003e\u0026middot;\u0026middot;\u0026middot;ClPEA\u003csup\u003e+\u003c/sup\u003e homodimer,\u003csup\u003e48\u003c/sup\u003e confirming the propensity of organic ammonium layers to establish Cl\u0026middot;\u0026middot;\u0026middot;Cl interaction at 1 atm and 2.5 GPa. Simultaneously, the Cl\u0026ndash;Cl bond energy at 2.5 GPa exceeded that at 1 atm, providing further evidence of pressure-intensified Cl\u0026middot;\u0026middot;\u0026middot;Cl interaction (Supplementary Fig.\u0026nbsp;29). Similarly, the ∆\u003cem\u003ed\u003c/em\u003e\u003csub\u003eBr\u003c/sub\u003e value, which continuously decreased from \u0026minus;\u0026thinsp;0.04 \u0026Aring; at 1 atm to \u0026minus;\u0026thinsp;0.14 \u0026Aring; at 1.7 GPa in (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, suggested the reinforcement of Br\u0026middot;\u0026middot;\u0026middot;Br interaction with pressure (Supplementary Fig.\u0026nbsp;28). The persistent absence of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was portended by Δ\u003cem\u003ed\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e \u0026gt; 0 (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef, and Supplementary Fig.\u0026nbsp;28).\u003c/p\u003e \u003cp\u003eTo further dissect the role of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions in the structural evolution of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, the changes in \u003cem\u003ed\u003c/em\u003e\u003csub\u003eP\u003c/sub\u003e and \u003cem\u003eδ\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e with pressure were explored (Supplementary Fig.\u0026nbsp;30 and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). With increasing pressure, interlayer shrinkage enhanced the interactions between organic amine layers, drawing organic amines closer to one another and reducing their penetration depth into the inorganic framework (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh and Supplementary Fig.\u0026nbsp;30). Enhanced Cl\u0026middot;\u0026middot;\u0026middot;Cl and Br\u0026middot;\u0026middot;\u0026middot;Br interactions in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e further drew organic amines away from the inorganic framework, which led to their \u003cem\u003ed\u003c/em\u003e\u003csub\u003eP\u003c/sub\u003e values being shallower than in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (Supplementary Fig.\u0026nbsp;30). As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed, the enhanced halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions guided the tilt and movement of the [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedron with pressure. During compression, the \u003cem\u003eδ\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e values of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e substantially decreased as Cl\u0026middot;\u0026middot;\u0026middot;Cl and Br\u0026middot;\u0026middot;\u0026middot;Br interactions were reinforced, reaching minimum values at 2.5 and 1.7 GPa, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). This finding corresponded to the pressures at which the strongest deep-blue CPL was observed in the PL spectra of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. When halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions were absent, the \u003cem\u003eδ\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e value slightly decreased and then rapidly increased in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, hindering deep-blue emission (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). Therefore, pressure-induced enhancement of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions substantially reduced the penetration depth of organic amines, effectively mitigating structural distortion of the inorganic Pb\u0026ndash;Br layer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eDensity functional theory (DFT) calculations.\u003c/b\u003e To clarify the photophysical mechanism underlying pressure-triggered deep-blue emission in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, DFT calculations of the electronic band structure and partial density of states of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e were performed. As shown in Supplementary Fig.\u0026nbsp;31, the valence band maximum of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was primarily attributed to the Br 4p and Pb 6s orbitals, while the conduction band minimum predominantly consisted of the Pb 6p orbitals. The organic component, acting as an electron barrier, did not contribute to the electronic states at the band edge due to its density of states being projected at a deeper energy level.\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e Therefore, the results indicated that the photophysical property evolution in (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was governed by the [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedral structure. The reduction in band gap energy at 2.5 GPa was attributed to enhanced orbital overlap due to the shortened Pb\u0026ndash;Br bond length (Supplementary Fig.\u0026nbsp;32). The progressive decrease in the band gap energy under pressure in (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was consistent with the continuous shortening of the Pb\u0026ndash;Br bond length (Supplementary Figs.\u0026nbsp;33\u0026ndash;35).\u003c/p\u003e \u003cp\u003eTheoretical analysis of excited states further suggested that pressure-induced deep-blue emission could be attributed to the facilitated de-trapping of the STE state, which was facilitated by the reduced transient elastic deformation within the inorganic lattice. The excited states involved in electron\u0026ndash;phonon coupling at 1 atm and 2.5 GPa are depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, respectively. The strong electron\u0026ndash;phonon coupling effect created by the distorted lattice at 1 atm effectively captured and confined excitons within the lattice, resulting in the localization of electrons and holes within a specific inorganic [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedron. By contrast, the diminished lattice distortion induced by increased Cl\u0026middot;\u0026middot;\u0026middot;Cl interaction at 2.5 GPa impeded electron\u0026ndash;phonon coupling, facilitating the unrestricted movement of electrons and holes within the lattice. The configuration coordinate diagrams of STE formation at 1 atm and 2.5 GPa are presented in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed, respectively. ΔE\u003csub\u003est\u003c/sub\u003e denotes the self-trapping depth, which refers to the difference between the STE and FE configurations in the excited state. High STE emission is frequently observed at greater self-trapping depths.\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e The calculated self-trapping depth at 1 atm (0.120 eV) surpassed that at 2.5 GPa (0.007 eV), suggesting a higher likelihood of STE radiative recombination at 1 atm than at 2.5 GPa. Therefore, (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals exhibited warm-white luminescence dominated by broadband STE emission at 1 atm (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee) and deep-blue luminescence led by narrow-band FE emission at 2.5 GPa (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Huang\u0026ndash;Rhys factor (\u003cem\u003eS\u003c/em\u003e) was employed to quantitatively describe electron\u0026ndash;phonon coupling strength, thereby facilitating a deeper understanding of the mechanism underlying pressure-induced deep-blue emission. The \u003cem\u003eS\u003c/em\u003e value is estimated by ΔE\u003csub\u003estokes\u003c/sub\u003e = 2\u003cem\u003eSћ\u003c/em\u003eω\u003csub\u003eLO\u003c/sub\u003e, where E\u003csub\u003estokes\u003c/sub\u003e represents the Stokes shift energy and ω\u003csub\u003eLO\u003c/sub\u003e represents the vibration energy of the longitudinal optical phonon.\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e The considerable decrease in \u003cem\u003eS\u003c/em\u003e value with increasing pressure in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e provided further evidence of effective suppression of the electron\u0026ndash;phonon coupling effect through pressure-induced Cl\u0026middot;\u0026middot;\u0026middot;Cl interaction enhancement (Supplementary Fig.\u0026nbsp;36). The \u003cem\u003eS\u003c/em\u003e value of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e far exceeded that of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, indicating that (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e tended to exhibit broadband STE emission due to stronger electron\u0026ndash;phonon coupling in the absence of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions (Supplementary Fig.\u0026nbsp;37). The evolution of \u003cem\u003eS\u003c/em\u003e values with pressure in (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was similar to that in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (Supplementary Fig.\u0026nbsp;38), demonstrating a sharp decrease in \u003cem\u003eS\u003c/em\u003e values with increasing pressure. This finding suggested that the enhancement of Cl\u0026middot;\u0026middot;\u0026middot;Cl and Br\u0026middot;\u0026middot;\u0026middot;Br interactions facilitated the de-trapping of the STE state back to the FE state by weakening electron\u0026ndash;phonon coupling. Furthermore, the short lifetime components in the STE emission lifetime of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e increased with pressure, further signifying that the STE state gradually de-trapped back to the FE state under compression (Supplementary Fig.\u0026nbsp;39 and Supplementary Table\u0026nbsp;7).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work, we successfully synthesized novel 2D chiral perovskites, (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, with discrepancies in halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions by employing halogen-substituted chiral organic amine and PbBr\u003csub\u003e2\u003c/sub\u003e. Pressure-driven enhancement of halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e achieved high color\u0026ndash;purity deep-blue CPL controlled by narrow-band FE emission under moderate pressure. Without halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions, (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e exhibited yellow light commanded by broadband STE emission under high pressure. The ADXRD and DFT results demonstrated that halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions played a crucial role in guiding the tilt and movement of the inorganic [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e octahedron under high pressure. Greatly diminished lattice distortion originating from reinforced halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions weakened electron\u0026ndash;phonon coupling, facilitating FE radiative recombination to realize deep-blue CPL in (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. By contrast, (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, without halogen\u0026middot;\u0026middot;\u0026middot;halogen interactions, was unable to achieve blue emission owing to the inability to prevent structural distortion.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eSynthesis of (\u003c/b\u003e \u003cb\u003eR\u003c/b\u003e \u003cb\u003e-3-XPEA)\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003ePbBr\u003c/b\u003e \u003csub\u003e \u003cb\u003e4\u003c/b\u003e \u003c/sub\u003e \u003cb\u003e(PEA\u0026thinsp;=\u0026thinsp;phenethylamine, X\u0026thinsp;=\u0026thinsp;F, Cl, Br).\u003c/b\u003e PbO (0.5 mmol) was dissolved in a mixed solution of 2 mL of concentrated aqueous HBr and 0.5 mL of concentrated aqueous H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e3\u003c/sub\u003e under heating and vigorous stirring until a clear solution was obtained. The temperature of the hot plate was set to 120 \u003csup\u003eo\u003c/sup\u003eC to keep the HBr solution boiling. The \u003cem\u003eR\u003c/em\u003e-3-XPEA (1 mmol) was added to 0.5 mL of concentrated aqueous HBr solution in a separate vial under stirring. The neutralized \u003cem\u003eR\u003c/em\u003e-3-XPEA solution was added to the boiling HBr solution under vigorous stirring. Then the temperature was lowered to 100 \u003csup\u003eo\u003c/sup\u003eC until colorless plate-shaped crystals started to precipitate out. Further decrease of the temperature to 60 \u003csup\u003eo\u003c/sup\u003eC resulted in precipitation of most of the crystals within 1h. Then the hot plate was turned off, and the solution was cooled slowly to room temperature.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCrystallographic data collection and refinement of the structure.\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eSingle-crystal X-ray diffraction analysis (SCXRD).\u003c/b\u003e SCXRD measurements of (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e were performed on a Bruker D8 VENTURE diffractometer with Mo-K\u003cem\u003eα\u003c/em\u003e radiation (λ\u0026thinsp;=\u0026thinsp;0.71073 \u0026Aring;). Data reduction was performed using the APEX3 software package. SCXRD measurement of (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e was performed on a Rigaku XtaLAB Pro diffractometer with Cu-K\u003cem\u003eα\u003c/em\u003e radiation (\u003cem\u003eλ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.54184 \u0026Aring;). Data collection and reduction were performed using the program \u003cem\u003eCrysAlis\u003c/em\u003e\u003csup\u003e\u003cem\u003ePro\u003c/em\u003e\u003c/sup\u003e. The three structures were all assessed with direct methods (SHELXS)\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e and refined by full-matrix least squares in F2 using OLEX2,\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e which utilizes the SHELXL-2015 module.\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e The crystal structures were visualized in DIAMOND 3.2.\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e Detailed information about the X-ray crystal data, intensity collection procedure and refinement results for (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (X\u0026thinsp;=\u0026thinsp;F, Cl, Br) are summarized in Supplementary Tables\u0026nbsp;1\u0026ndash;6.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePowder X-ray diffraction (PXRD)\u003c/b\u003e. PXRD patterns of the (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e samples were recorded on a D/MAX-3D diffractometer (Cu Kα, λ\u0026thinsp;=\u0026thinsp;1.54178 \u0026Aring;). Simulated powder patterns were obtained with Mercury software and a crystallographic information file (CIF) from a single-crystal X-ray experiment.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCircularly polarized luminescence (CPL).\u003c/b\u003e CPL spectra were obtained by a JASCO CPL-300 spectropolarimeter in the solid state. Each CPL spectrum was the average of at least three scans. The degree of chirality can be quantified by the anisotropy factor \u003cem\u003eg\u003c/em\u003e\u003csub\u003elum\u003c/sub\u003e, which is defined as \u003cem\u003eg\u003c/em\u003e\u003csub\u003elum\u003c/sub\u003e = 2(I\u003csub\u003eL\u003c/sub\u003e \u0026minus; I\u003csub\u003eR\u003c/sub\u003e)/(I\u003csub\u003eL\u003c/sub\u003e + I\u003csub\u003eR\u003c/sub\u003e), where I\u003csub\u003eL\u003c/sub\u003e and I\u003csub\u003eR\u003c/sub\u003e represent the photoluminescence intensity of left- and right-circularly polarized light respectively.\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eAnalysis of octahedral distortion.\u003c/b\u003e The degree of octahedral distortion was determined by using the parameter \u003cem\u003eδ\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/em\u003e\u003c/sup\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\delta\\:}^{2}=\\frac{1}{11}\\sum\\:_{i=1}^{12}{\\left(\\text{\u0026theta;}\\text{i}-\\text{90}\\right)}^{2}\\)\u003c/span\u003e\u003c/span\u003e, where \u003cem\u003eθ\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e represents the individual Br-Pb-Br bond angles of the octahedron.\u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eHigh-pressure Generation.\u003c/b\u003e High-pressure experiments were carried out with a symmetric-type diamond-anvil cell (DAC) with a pair of 300 \u0026micro;m culets. The sample and a small ruby ball were loaded into the 150 \u0026micro;m-diameter chamber of a DAC, constructed from a T301 steel gasket pre-indented to a thickness of 45 \u0026micro;m. In high-pressure experiments, silicon oil was utilized as the pressure transmitting medium (PTM) for optical absorption, PL, TRPL, Raman and ADXRD experiments. The PTM did not have any detectable effect on the behavior of (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e under pressure. All of the measurements were performed at room temperature.\u003c/p\u003e \u003cp\u003e \u003cb\u003eIn situ high-pressure optical measurements.\u003c/b\u003e PL spectra were measured by using a 360 nm laser excitation. Absorption spectra were measured by using a deuterium-halogen light source (Ocean Insight DH-2000-BAL) and a fiber spectrometer of Ocean Insight QEP03490. PL and optical micrographs of the samples were obtained using a camera (Olympus DP74) equipped with a microscope (Olympus BX53). The camera can record the photographs under the same conditions including exposure time and intensity. Raman spectra were collected in a MonoVista CRS\u0026thinsp;+\u0026thinsp;spectrometer with a 532 nm laser excitation. The TRPL spectra were performed using a homemade spectroscopy system (Ideaoptics, Shanghai, China) with a 375 nm laser as the excitation source. The measured PL decay curves were fitted using double exponential functions I(t)\u0026thinsp;=\u0026thinsp;I(0) \u0026times; [A\u003csub\u003e1\u003c/sub\u003e \u0026times; exp(-t/τ\u003csub\u003e1\u003c/sub\u003e)\u0026thinsp;+\u0026thinsp;A\u003csub\u003e2\u003c/sub\u003e \u0026times; exp(-t/τ\u003csub\u003e2\u003c/sub\u003e)].\u003c/p\u003e \u003cp\u003eWe performed in situ high-pressure ADXRD measurements with the wavelength of 0.6199 \u0026Aring; at the 4W2 beamline at the High-Pressure Station of the Beijing Synchrotron Radiation Facility. We used CeO\u003csub\u003e2\u003c/sub\u003e as a standard sample to do the calibration. The 2D Debye-Scherrer diffraction rings were recorded using an imaging plate detector and integrated into the 1D profile using the Dioptas program. All high-pressure experiments were conducted at room temperature.\u003c/p\u003e \u003cp\u003e \u003cb\u003eComputational Details.\u003c/b\u003e Density functional theory (DFT) calculations are performed using the plane-wave pseudopotential as implemented in the Vienna Ab-initio Simulation Package (VASP).\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e The electron-core interactions are described with the frozen-core projector-augmented wave pseudopotentials.\u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e The generalized gradient approximation formulated by Perdew, Burke, and Ernzerhof (PBE) as the exchange-correlation functional with cutoff energies of 520 eV was chosen in all of the calculations.\u003csup\u003e\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e The total energy convergence criteria is 1.0 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e eV and the force on each atom converges to 0.01 eV \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e in optimizing the geometric structure. The vdW interaction is considered by using the DFT-D3 method of Grimme.\u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e Pressure values are calculated through the relation P = -\u0026part;E/\u0026part;V, where E is the energy of the crystal and V is the cell volume.\u003c/p\u003e \u003cp\u003eThe spin-orbit coupling (SOC) effect is important in cubic lead halide perovskites. We test the band gap of the 2D lead bromide perovskite (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. The PBE calculated band gap energy is 2.79 eV. The without and with HSE06 calculated band gaps are 3.56 eV and 2.86 eV, respectively. Thus, the PBE is only 0.29 eV smaller than the experiment band gap of 3.08 eV. The reason for 2D and 1D lead halide perovskites, the SOC is significantly quenched due to the crystal field splitting of the Pb 6\u003cem\u003ep\u003c/em\u003e orbitals. Since the SOC induced effective mass change is also minor in 2D perovskites, the effect on the self-trapping is expected to be small.\u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e Therefore, we neglect the SOC effect on the STE calculations.\u003c/p\u003e \u003cp\u003eTo study the STE properties, a 2\u0026times;2\u0026times;1 supercell containing 376 atoms with Γ only \u003cem\u003ek\u003c/em\u003e point is used in the calculations. The excited states were achieved by the constrained occupancy method. The triplet STE state was achieved by setting the spin quantum number. Following Wang et al.\u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e, the configurational coordinate diagrams were constructed by linear interpolating the coordinates between the ground and STE configurations then the total energies both of the ground and excited STE state at each coordinate can be got. The coordinate difference between the ground and STE is \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:\\text{Q}=\\sqrt{{\\sum\\:}_{k,i}{m}_{k}({R}_{k,i}^{e}-{R}_{k,i}^{g})}\\)\u003c/span\u003e\u003c/span\u003e, where \u003cem\u003ek\u003c/em\u003e labels the atoms, \u003cem\u003ei\u003c/em\u003e = (x, y, z), \u003cem\u003em\u003c/em\u003e is the atomic mass, and \u003cem\u003eR\u003c/em\u003e is the atomic coordinates with \u003cem\u003ee\u003c/em\u003e and \u003cem\u003eg\u003c/em\u003e for the excited and ground state, respectively. Note that the underestimated 0.29 eV band gap arising from DFT-PBE compared with the experiment value was corrected with the scissor method in the configurational coordinate diagrams.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTheoretical calculation of weak interaction calculations.\u003c/b\u003e The initial step involved extracting the dimeric structure from the crystal lattice. Subsequently, we performed structural optimization and vibrational analysis, concentrating on the hydrogen atom. Utilizing the Gaussian 16 software package, \u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e we employed the B3LYP functional \u003csup\u003e\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e and D3BJ dispersion correction\u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e for tasks such as structural optimization and vibration analysis. The optimized molecular structures and vibration analysis were determined using the 6-31G* basis set. \u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e For weak interaction calculations, we utilized the M06-2X functional \u003csup\u003e\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e and the ma-def2-TZVP basis sets \u003csup\u003e\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e\u003c/sup\u003e. Additionally, a thorough analysis of weak interactions was carried out using the Interaction Region Indicator (IRI) \u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e with Multiwfn 3.8 \u003csup\u003e71\u003c/sup\u003e. To visualize the system's structure and weak interactions, we employed VMD \u003csup\u003e\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability.\u0026nbsp;\u003c/strong\u003eData supporting the findings of this manuscript are available from the corresponding authors upon reasonable request.\u0026nbsp;The X-ray crystallographic coordinates for structures reported in this article have been deposited at the Cambridge Crystallographic Data Centre (CCDC) under deposition numbers CCDC: 2327085 (\u003cstrong\u003e(\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e), 2327086 (\u003cstrong\u003e(\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e), and 2327087 (\u003cstrong\u003e(\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Key R\u0026amp;D Program of China (2021YFA1200301), the National Natural Science Foundation of China (nos. 92061201, 21825106, 52103238), Zhongyuan Thousand Talents (Zhongyuan Scholars) Program of Henan Province (234000510007), the China Postdoctoral Science Foundation (nos. 2021TQ0289, 2021M700128, 2023T160197 and 2022M711061), and Zhengzhou University. The in situ high-pressure powder XRD was performed at 4W2 HP-Station in the Beijing Synchrotron Radiation Facility (BSRF) and BL15U1 Station in the Shanghai Synchrotron Radiation Facility (SSRF).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026dagger;\u003c/sup\u003e M.-E. Sun, F. Wang and M. He contributed equally to this work. S.-Q. Zang, Y. Wu and G. Chen supervised the project. M.-E. Sun, Y.-N. Yang, J.-K. Yang, and X.-J Zhang synthesized the crystals and\u0026nbsp;characterized the material properties in high-pressure. F. Wang carried out first principles DFT calculations. Y. Wang, Y. Fu and Q. Li revised the\u0026nbsp;manuscript. J. Lei and Z. Wang participated in discussions and gave much helpful suggestion. M.-E. Sun,\u0026nbsp;M. He\u0026nbsp;and\u0026nbsp;G. Chen wrote the paper, and all the authors read and commented on the paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupplementary information is available in the online version of the paper. Reprints and permissions information is available online at www.nature.com/reprints. Correspondence and requests for materials should be addressed to S.-Q. Zang.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting financial interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eGrancini G. \u0026amp; Nazeeruddin M. K., Dimensional tailoring of hybrid perovskites for photovoltaics. \u003cem\u003eNat. Rev. 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Herein, the FE emission behaviors of three new 2D chiral perovskites, (\u003cem\u003eR\u003c/em\u003e-3-XPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (PEA = phenethylamine, X = F, Cl, Br), were investigated under hydrostatic pressure. (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e exhibited high color–purity deep-blue circularly polarized luminescence (CPL) dominated by FE at pressures of 1.7 and 2.5 GPa, respectively, whereas (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e presented broadband warm-white CPL under high pressure. The structural analysis and theoretical calculation results demonstrated that pressure reduced the penetration depths of \u003cem\u003eR\u003c/em\u003e-3-BrPEA\u003csup\u003e+\u003c/sup\u003e and\u003cem\u003e R\u003c/em\u003e-3-ClPEA\u003csup\u003e+\u003c/sup\u003e\u003cem\u003e \u003c/em\u003einto [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4-\u003c/sup\u003e inorganic frameworks by strengthening halogen···halogen (Br···Br and Cl···Cl) interactions between organic amines, resulting in smaller [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4-\u003c/sup\u003e octahedral distortion and weaker electron–phonon coupling in (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. Thus, pressure-driven enhancement of halogen···halogen interactions was responsible for remarkable deep-blue CPL in (\u003cem\u003eR\u003c/em\u003e-3-BrPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-3-ClPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. Conversely, [PbBr\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4-\u003c/sup\u003e octahedral distortion and strong electron–phonon coupling could not be effectively suppressed in (\u003cem\u003eR\u003c/em\u003e-3-FPEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e owing to the lack of halogen···halogen interactions, leading to the absence of deep-blue CPL. Our work gives a new insight into the intrinsic structure-property relationship between noncovalent interactions and the ultrahigh-color-purity emission behavior in chiral perovskites.\u003c/p\u003e","manuscriptTitle":"Halogen-Dependent Deep-Blue Circularly Polarized Emitters with Ultrahigh-Color-Purity Under High Pressure","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-18 07:14:20","doi":"10.21203/rs.3.rs-4687727/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b5497d1b-6a2a-48b8-956a-0c760361d8f9","owner":[],"postedDate":"July 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":34660190,"name":"Physical sciences/Chemistry/Inorganic chemistry"},{"id":34660191,"name":"Physical sciences/Chemistry/Materials chemistry"}],"tags":[],"updatedAt":"2024-12-20T15:00:18+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-18 07:14:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4687727","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4687727","identity":"rs-4687727","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}