The development of high-performance near-infrared organic light-emitting diodes is hindered by strong non-radiative processes as governed by the energy gap law. Here, we show that exciton ...delocalization, which serves to decouple the exciton band from highly vibrational ladders in the S0 ground state, can bring substantial enhancements in the photoluminescence quantum yield of emitters, bypassing the energy gap law. Experimental proof is provided by the design and synthesis of a series of new Pt(ii) complexes with a delocalization length of 5–9 molecules that emit at 866–960 nm with a photoluminescence quantum yield of 5–12% in solid films. The corresponding near-infrared organic light-emitting diodes emit light with a 930 nm peak wavelength and a high external quantum efficiency up to 2.14% and a radiance of 41.6 W sr−1 m−2. Both theoretical and experimental results confirm the exciton–vibration decoupling strategy, which should be broadly applicable to other well-aligned molecular solids.Pt(ii) complexes allow the fabrication of efficient near-infrared organic light-emitting diodes that operate beyond the 900 nm region.
Apart from numerous applications, for example in azo dye precursors, explosives, and industrial processes, the nitro group (−NO2) appears on countless molecules in photochemical research owing to its ...unique characteristics such as a strong electron‐withdrawing ability and facile conversion to the reduced substituent. Although it is well known as a fluorescence quencher, fluorescent chromophores that contain the nitro group have also emerged, with 3‐nitrophenothiazine being recently reported to have 100 % emission quantum yield in nonpolar solvents. The diverse characters of nitro‐containing chromophores motivated us to systematically review those chromophores with nitro substituents, their associated photophysical properties, and applications. In this Review, we succinctly elaborate the advance of the fluorescent nitro chromophores in fields of intramolecular charge transfer, fluorescent probes and nonlinear properties. Special attention is paid to the rationalization of the associated emission spectroscopy, so that the readers can gain insights into the structure‐photophysics relationship and hence gain insights for the strategic design of nitro chromophores.
Say NO2 to quenching: The nitro group is a well‐known fluorescence quencher, however, nitro‐substituted chromophores with considerable photoluminescence quantum yields have been reported. This Review systematically organizes a number of reports concerning fluorescent nitro compounds with detailed explanations of their photophysical properties, which provides guidelines for designing emissive nitro‐containing molecules.
Research into organic light emitters employing multiple resonance-induced thermally activated delayed fluorescence (MR-TADF) materials is presently attracting a great deal of attention due to the ...potential for efficient deep-blue emission. However, the origins and mechanisms of successful TADF are unclear, as many MR-TADF materials do not show TADF behaviour in solution, but only as particular pure solids. Here, an investigation into a well-known MR-TADF material, DABNA-1, together with other new MR materials (9H-quinolino3,2,1-klphenothiazin-9-one (QPO) and 9H-quinolino-3,2,1-kl-phenothiazin-9-one 5,5-dioxide (QP3O)), yields new insights regarding the origin of TADF. Although a material system may support the concept of MR, inefficiency in both forward and reverse intersystem crossings forbids TADF unless a suitable host material allows an exciplex-like host–emitter interaction that boosts TADF. This boosted-TADF mechanism can be generalized to any fluorescence dye that lacks TADF in the photoluminescence measurement but has a thermally accessible S1–T1 energy gap, opening the way to high-performance organic light-emitting diodes.This study reveals the importance of host–guest interactions for effective multiple-resonance thermally activated delayed fluorescence in organic light emitters.
Through the incorporation of various halogen‐substituted chiral organic cations, the effects of chiral molecules on the chiroptical properties of hybrid organic–inorganic perovskites (HOIPs) are ...investigated. Among them, the HOIP having a Cl‐substituted chiral cation exhibits the highest circular dichroism (CD) and circular polarized luminescence (CPL) intensities, indicating the existence of the largest rotatory strength, whereas the F‐substituted HIOP shows the weakest intensities. The observed modulation can be correlated to the varied magnetic transition dipole of HOIPs, which is sensitive to the d‐spacing between inorganic layers and the halogen–halogen interaction between organic cations and the inorganic sheets. These counteracting effects meet the optimal CD and CPL intensity with chlorine substitution, rendering the rotatory strength of HOIPs arranged in the order of (ClMBA)2PbI4>(BrMBA)2PbI4>(IMBA)2PbI4>(MBA)2PbI4>(FMBA)2PbI4.
Through the incorporation of Cl‐substituted chiral organic cations, the chiroptical properties of 2D chiral perovskites can be significantly enhanced. The observed circular dichroism and circular polarized luminescence intensities are found to be associated with the d‐spacing of hybrid organic–inorganic perovskites and the strength of the halogen–halogen interaction within the system.
The correlation between molecular packing structure and its room-temperature phosphorescence (RTP), hence rational promotion of the intensity, remains unclear. We herein present racemism enhanced RTP ...chiral chromophores by 2,2-bis-(diphenylphosphino)-1,1-napthalene (rac-BINAP) in comparison to its chiral counterparts. The result shows that rac-BINAP in crystal with denser density, consistent with a long standing Wallach's rule, exhibits deeper red RTP at 680 nm than that of the chiral counterparts. The cross packing between alternative R- and S- forms in rac-BINAP crystal significantly retards the bimolecular quenching pathway, triplet-triplet annihilation (TTA), and hence suppresses the non-radiative pathway, boosting the RTP intensity. The result extends the Wallach's rule to the fundamental difference in chiral-photophysics. In electroluminescence, rac-BINAP exhibits more balanced fluorescence versus phosphorescence intensity by comparison with that of photoluminescence, rendering a white-light emission. The result paves an avenue en route for white-light organic light emitting diodes via full exploitation of intrinsic fluorescence and phosphorescence.
Phenothiazine derivatives based on the 10‐phenyl‐10H‐phenothiazine (NAS) chromophore, namely 7‐phenyl‐7H‐benzocphenothiazine (NAS‐1) and 12‐phenyl‐12H‐benzoaphenothiazine (NAS‐2), were designed and ...synthesized. NAS‐1 and NAS‐2 are constitutional isomers with different steric strains imposed on the phenothiazine core moiety. In solution, the more‐strained NAS‐2 possesses a bent structure and undergoes photoinduced structural planarization (PISP). In the crystal, despite the absence of PISP, bent NAS‐2 exhibits prominent excimer emission as well as emission mechanochromism, which is not observed in the planar‐like NAS and NAS‐1. This unconventional observation results from the bent core structure facilitating π–π stacking of the peripheral naphthalene moieties. Two‐photon‐coupled depth‐dependent emission shows spectral differences between the surface and kernel of the NAS‐2 crystal, and is believed to be a general phenomenon, at least in part, for materials exhibiting emission mechanochromism.
In ′plane′ view: Phenothiazine derivatives were designed and synthesized. In solution, the more‐strained structure (see image) possesses a bent structure and undergoes photoinduced structural planarization (PISP). In the crystal, despite the absence of PISP, it exhibits prominent excimer emission as well as emission mechanochromism.
Tin perovskite nanomaterial is one of the promising candidates to replace organic lead halide perovskites in lighting applications. Unfortunately, the performance of tin-based systems is markedly ...inferior to those featuring toxic Pb salts. In an effort to improve the emission quantum efficiency of nanoscale 2D layered tin iodide perovskites through fine-tuning the electronic property of organic ammonium salts, we came to unveil the relationship between dielectric confinement and the photoluminescent properties of tin iodide perovskite nanodisks. Our results show that increasing the dielectric contrast for organic versus inorganic layers leads to a bathochromic shift in emission peak wavelength, a decrease of exciton recombination time, and importantly a significant boost in the emission efficiency. Under optimized conditions, a leap in emission quantum yield to a record high 21% was accomplished for the nanoscale thienylethylammonium tin iodide perovskite (TEA2SnI4). The as-prepared TEA2SnI4 also possessed superior photostability, showing no sign of degradation under continuous irradiation (10 mW/cm2) over a period of 120 h.
The weak fluorescence (quantum yield <1 % in cyclohexane) of phenothiazine (PTZ) impedes its further application. In addition, the nitro group (NO2) is a well‐known fluorescence quencher. ...Interestingly, we obtained a highly fluorescent chromophore by combining these two moieties, forming 3‐nitrophenothiazine (PTZ‐NO2). For comparison, a series of PTZ derivatives bearing electron‐withdrawing groups (EWGs; CN and CHO) or electron‐donating groups (EDGs; OMe) at the 3‐position have been designed and synthesized. The phenothiazines bearing EWGs exhibited enhanced emission compared with the parent PTZ or EDG derivatives. Computational approaches unveiled that for PTZ and PTZ‐OMe, the transitions are from HOMOs dominated by π orbitals to LUMOs of mixed sulfur nonbonding–π* orbitals, and hence are partially forbidden. In contrast, the EWGs lower the energy level of the lone‐pair electrons on the sulfur atom, thereby suppressing the mixing of the nonbonding orbital with the π* orbital in the LUMO, such that the allowed ππ* transition becomes dominant. This work thus demonstrates a judicious chemical design to fine‐tune the transition character in PTZ analogues, with PTZ‐NO2 attaining 100 % emission quantum yields in nonpolar solvent.
Fine‐tuning fluorescence: A series of 3‐substituted phenothiazines (PTZ) with different electron‐donating and ‐withdrawing groups have been investigated by comprehensive computational approaches and photophysical measurements. Of these, the nitro‐substituted PTZ achieves a quantum yield of 100 % in nonpolar solvent (see scheme). The results validate that the interplay of the nonbonding orbital of the sulfur atom in PTZ plays a crucial role in the electronic transition.
2D perovskites with chemical formula A′2An−1BnX3n+1 have recently attracted considerable attention due to their tunable optical and electronic properties, which can be attained by varying the ...chemical composition. While high color‐purity emitting perovskite nanomaterials have been accomplished through changing the halide composition, the preparation of single‐phase, specific n‐layer 2D perovskite nanomaterials is still pending because of the fast nucleation process of nanoparticles. We demonstrate a facile, rational and efficacious approach to synthesizing single‐phase 2D perovskite nanoplates with a designated n number for both lead‐ and tin‐based perovskites through kinetic control. Casting carboxylic acid additives in the reaction medium promotes selective formation of the kinetic product—multilayer 2D perovskite—in preference to the single‐layer thermodynamic product. For the n‐specific layered 2D perovskites, decreasing the number of octahedral layers per inorganic sheet leads to an increase of photoluminescence energy, radiative decay rate, and a significant boost in photostability.
Single‐phase 2D lead‐ and tin‐based perovskite nanoplates with a designated n value can be successfully prepared through kinetic control of the nucleation process. This approach can effectively avoid the multipeak photoluminescence generally observed in multilayer 2D perovskite nanomaterials.
The photophysical properties of the phenothiazine-triphenyltriazine derivative, PTZ-TRZ, are reinvestigated. The results, in combination with the computational approaches, lead us to draw the ...conclusion that the complicated excitation behavior in toluene (ref ), in part, is due to the UV absorption cutoff region for toluene where the <315 nm excitation is greatly distorted by solvent absorption, i.e., the inner filter effect, in a regular sample cuvette (1.0 cm path length). Switching the solvent to cyclohexane with the UV cutoff wavelength at 235 nm simplifies the results. In cyclohexane, two isomers exist for PTZ-TRZ in the ground state and quasi-axial and quasi-equatorial conformers. Upon electronic excitation, both quasi-axial and quasi-equatorial conformers undergo structural relaxation to an energy minimum state where the phenothiazine is in a planar configuration.
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