Delicate modulation of triplet energy levels for activating “hot excitons” channels in deep red AIEgens

Abstract

The “hot excitons” (HE) concept has played an important role in developing high-performance and stable emitting devices with low-efficiency roll-off; however, to date, reports about how to activate the HE process by systematic molecular structure regulation have been rare. Herein, four naphthothiadiazole-based deep red (DR) emitters with aggregation-induced emission (AIE)-activity are employed as model compounds to reveal referenced structure–property rules in excited states containing large energy level differences between T₂ and T₁ levels (ΔT₂T₁), small energy splits (ΔE_st) and large spin–orbit coupling (SOC), and effective interstate coupling between S₁ and S₂. These rules are presented as “Three Golden Principles” because of their acceleration effect in improving emissive exciton transformation from high-level triplet excitons by activating the upper reversed intersystem crossing (uRISC) channel. A series of spectral measurements and the establishment of the theoretical model were achieved, which have an important guiding significance in designing HE-based organic light-emitting diodes (OLED) with high performance and stable roll-off.