Efficient deep-red hot exciton electroluminescent emitters with fine-tuning of excited states via locally large twisted conformation

Abstract

The precise regulation of excited state is a challenge to emitters for achieving highly efficient non-doped deep-red electroluminescence (EL). Herein, we used triphenylamine and phenoxazine as donors and benzo[c][1,2,5]thiadiazole as an acceptor to construct a hot exciton skeleton. Then chemically modified the phenoxazine by locally large twisted conformation to obtain N,N-diphenyl-4-(7-(10-phenyl-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)aniline (TPAPH), 4-(7-(10-(4-ethoxyphenyl)-10H-phenoxazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)-N,N-diphenylaniline (TPAPHOC2), and 4-(3-(7-(4-(diphenylamino)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)-10H-phenoxazin-10-yl)benzonitrile (TPAPHCN), thereby achieving excited state perturbation. As a result, three emitters exhibited aggregation-induced emission enhancement and hybridized local and charge transfers characteristics based on photophysical experimentals. In EL, the TPAPH-, TPAPHOC2-, and TPAPHCN-based non-doped devices achieved deep-red emission with Commission International de L’Eclairage coordinates of (0.68, 0.32), (0.69, 0.31), and (0.66, 0.34) and with emission peaks at 660, 669, and 647 nm, respectively. The maximum external quantum efficiencies were 5.3%, 3.7%, and 6.0%, respectively. The results of this study not only realize the non-doped deep-red OLEDs with high performance but also indicate that the presence of locally large twisted conformation presented an efficient manner for exploring precise excited state tuning for fluorescent emitter.