Adjusting the photophysical properties of AIE-active TADF emitters from through-bond to through-space charge transfer for high-performance solution-processed OLEDs

Abstract

Intramolecular through-space charge transfer (TSCT) excited state has been exploited for developing thermally activated delayed fluorescence (TADF) emitters, while the adjustment of excited state dynamics by conformational engineering is still rare. Herein, we designed a series of AIE-active TADF emitters, bearing triphenylamine as donor and phenyl ketone as acceptor unit, and the evolution of charge transfer from through-bond to through-space is realized by controlling the relative position of the donor and acceptor units. Upon transforming the charge transfer categories from through-bond to through-space, the reverse intersystem crossing (RISC) rate is progressively improved by virtue of the narrower energy split between singlet and triplet states (ΔΕST), meanwhile, the restricted intramolecular motion suppresses the non-radiative decay effectively, resulting in obviously improved luminescence efficiency. Appointing a bipolar blue TADF material as host to sensitize these emitters, solution-processed organic light-emitting diodes (OLEDs) based on TSCT emitter 1TCPM-Cz achieve maximum current efficiency (CE) of 35.5 cd A−1 and external quantum efficiency (EQE) of 13.3%, respectively, which is higher than that of through-bond charge transfer (TBCT) analogues. The work demonstrates a convenient design strategy to achieve high-performance TSCT emitters by regulating the conformation of the donor and acceptor.