The triad types of molecules with various combinations of electron donors (D) and acceptors (A) have been widely explored in optoelectronics. However, their photophysical and photochemical properties, which are frequently unconventional, are relatively unexplored. In this study, a donor–donor–acceptor (D–D–A)-type triad, CTPS, consisting of the donor moiety of triphenylamine (D1) and the acceptor moiety of dibenzothiophene sulfone (A) bridging through the second donor carbazole (D2) into a U-shape configuration, was synthesized. CTPS exhibited dual emission bands, both of which reveal solvent-polarity-dependent solvatochromism and unusual excitation-wavelength-dependent ratiometric emission. Comprehensive studies clarified that two emissions originate from two different D–A charge-transfer (CT) states. The lower-energy CT­(S) state possesses D1 → A through-space CT nature with optically forbidden transition, whereas the higher-lying CT­(B) state is associated with optically allowed D2 → A CT through the π-conjugation transition. Upon S0 → CT­(B) excitation, the charge transfer creates D2δ+Aδ− dipolar changes and Aδ−–D1 repulsion, leading to structural relaxation of the CT­(B) state that competes with fast CT­(B) → CT­(S) internal conversion. Therefore, despite the fact that they originate from the same Franck–Condon excited state, both energy-stabilized CT­(B) and CT­(S) states are populated through two independent channels. The stabilized CT­(B) and CT­(S) states possess different optimized geometries and do not interconvert during their lifespans, rendering different population decay time constants. The slim highest occupied molecular orbital/lowest unoccupied molecular orbital overlapped D1–A CT­(S) state exhibits thermally activated delayed fluorescence (TADF), the character of which was further exploited as a host in organic light-emitting diode. The results gain new insights into the properties of the bending-type D–D–A TADF triads. CTPS should not be a unique case. Bizarre photophysical behavior encountered in molecules comprising multiple D and A groups may involve the interplay among various local CT states, which might have been overlooked.

Four diplatinum(II) complexes with the formula [Pt(pypm)(μ-F n )] 2 (2, 3a−c) bearing both a pyridine-pyrimidinate chelate and formamidinate bridge, where (pypm)H and F n H stand for 5-(pyridin-2-yl)-2-(trifluoromethyl)pyrimidine and functional formamidines with various substituents of i Pr (n = 1), Ph (n = 2), C 6 H 4 t Bu (n = 3), and C 6 H 4 CF 3 (n = 4), were synthesized en route from a mononuclear intermediate represented by [Pt(pypm)Cl-(F 1 H)] (1). Single-crystal X-ray diffraction studies confirmed the structure of 1 and 3a comprised of an individual "Pt(pypm)" unit and two "Pt(pypm)" units with a Pt•••Pt distance of 2.8845(2) Å, respectively. Therefore, in contrast to the structured emission of mononuclear 1 with the first vibronic peak wavelength at 475 nm, all other diplatinum complexes with shortened Pt•••Pt separation exhibited greatly red shifted and structureless metal−metal to ligand charge transfer (MMLCT) emission that extended into the near-infrared region in solid states. Their photophysical characteristics were measured under three distinctive morphological states (i.e., crystals, sublimed powders, and vacuum-deposited thin films) by steady-state UV−vis spectroscopy, while retention of Pt•••Pt interactions in deposited thin films of 2 and 3a−c was confirmed using Raman spectroscopy, demonstrating lowered Pt•••Pt stretching at 80−200 cm −1 . Most importantly, complexes 3a−c exhibited a gradual red shift with the trends crystals < sublimed powders < vacuum-deposited thin films, a result of increased intermolecular π−π stacking interactions and Pt•••Pt interactions, while crystalline samples exhibited the highest luminescence among all three morphological states due to the fewest defects in comparison to other morphologies. Finally, 3b was selected as a nondoped emitter for the fabrication of NIR-emitting OLEDs, giving an electroluminescence peak at 767 nm and a maximum external quantum efficiency of 0.14% with negligible roll-off.

Phenothiazine derivatives based on the 10-phenyl-10H-phenothiazine (NAS)c hromophore,n amely 7-phenyl-7H-benzo[c]phenothiazine (NAS-1)a nd 12-phenyl-12Hbenzo[a]phenothiazine (NAS-2), were designed and synthesized. NAS-1 and NAS-2 are constitutional isomers with different steric strains imposed on the phenothiazine core moiety.Insolution, the more-strained NAS-2 possesses abent 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.T his unconventional observation results from the bent core structure facilitating p-p stacking of the peripheral naphthalene moieties.T wo-photon-coupled depthdependent emission shows spectral differences between the surface and kernel of the NAS-2 crystal, and is believed to be ageneral phenomenon, at least in part, for materials exhibiting emission mechanochromism. Photoinducedstructuralplanarization(PISP)isafascinatingand promising phenomenon that has received much attention. [1] Recent examples are focused on the class of molecules bearing an N,N'-disubstituted-dihydrodibenzo[a,c]phenazine chromophore (DPAC ;s ee Figure 1a). [2] Different from the early reported PISP molecules that reveal an intrinsic nonplanar structure free from steric perturbation, [2] bent DPACs are purportedly ar esult of the steric hindrance imposed on the DPAC moiety,which, upon optical excitation, undergoes structural planarization resulting in al arge Stokes-shifted emission. By exploiting the resulting structure-dependent emission properties,d iverse applications of PISP molecules have been reported, including white-light generation, [3] hydrolysis, [2d] and sensing for self-assembled metallacycles. [2a] To generalize,a sw ell as extend the scope of PISP compounds,i nt his study,anew class of compounds bearing phenothiazine was synthesized, including 10-phenyl-10Hphenothiazine (NAS), 7-phenyl-7H-benzo[c]phenothiazine (NAS-1), and 12-phenyl-12H-benzo[a]phenothiazine (NAS-2; Figure 1a). NAS-1 and NAS-2 are strategically designed to act as constitutional isomers,but are subject to different steric strains in the core chromophore benzophenothiazine.The aim of this study is twofold. Firstly,w ei ntend to explore if heterocyclic systems other than DAPC are able to undergo PISP,broadening its utility in chemistry.Secondly,byaccessing isomers with distinct steric strain, the mechanism of the structure-PISP relationship can be explored. Also,p henothiazines are emerging materials which have been recently reported to show persistently long phosphorescence suitable for potential applications in bioimaging. [4] As ar esult, NAS-2,w hich possesses am arkedly bent structure,undergoes prominent PISP,generalizing the mechanism of PISP governed by steric hindrance.Moreover,inthe solid state,u nlike the conventional stacking planar structure induced excimeric reaction, [5] the bent NAS-2 reveals anomalous excimer formation ...

Five N-borylated TADF emitters bearing both boron dimesityl acceptor and methoxy substituted carbazole are presented with electroluminescence ranging from 444 to 468 nm, and with the best maximum external quantum efficiency of 13.3%.

Herein, we introduce the cyclic 8p-electron (C8p) molecule N,N'-diaryl-dihydrodibenzo[a,c]phenazine (DPAC) as a dual-functional donor to establish a series of new donorlinker-acceptor (D-L-A) dyads DLA1-DLA5. The excitedstate bent-to-planar dynamics of DPAC regulate the energy gap of the donor, while the acceptors A1-A5 are endowed with different energy gaps and HOMO/LUMO levels. As a result, the rate and efficiency of the excited-state electron transfer vs. energy transfer can be finely harnessed, which is verified via steady-state spectroscopy and time-resolved emission measurements. This comprehensive approach demonstrates, for the first time, the manifold of excited-state properties governed by bifunctional donor-based D-L-A dyads, including bent-toplanar, photoinduced electron transfer (PET) from excited donor to acceptor (oxidative-PET), fluorescence resonance energy transfer (FRET), bent-to-planar followed by electron transfer (PFET), and PET from donor to excited acceptor (reductive-PET).