The regioisomeric effect on the excited-state fate leading to room-temperature phosphorescence or thermally activated delayed fluorescence in a dibenzophenazine-cored donor–acceptor–donor system

Abstract

Exploring the design principle for switching between thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) is a fundamentally important research to develop triplet-mediated photofunctional organic materials. Herein systematic studies on the regioisomeric and substituent effects in a twisted donor–acceptor–donor (D–A–D) molecular scaffold (A = dibenzo[a,j]phenazine; D = dihydrophenazasiline) on the fate of its excited state have been performed. The study revealed that regioisomerism clearly affects the emission behavior of the D–A–D compounds. Moreover, distinct differences in TADF, dual TADF & RTP, and dual RTP were observed, depending on the host used. Furthermore, organic light-emitting diodes (OLEDs) fabricated with the developed emitters achieved high external quantum efficiencies (EQEs) of up to 7.4% for RTP-based OLEDs.