Simultaneously Enhanced Reverse Intersystem Crossing and Radiative Decay in Thermally Activated Delayed Fluorophors with Multiple Through‐space Charge Transfers

Abstract

AbstractThermally activated delayed fluorescence (TADF) materials with through‐space charge transfers (CT) have attracted particularly interest recently. However, the slow reverse intersystem crossing (RISC) and radiative decay always limit their electroluminescence performances. Herein, TADF molecules with ortho‐linked multiple donors‐acceptor (ortho‐Dn‐A) motif are developed to create near‐degenerate excited states for the reinforcement of spin‐orbit coupling. The incorporation of both through‐bond and through‐space CT enlarges oscillator strength. The optimal ortho‐D3‐A compound exhibits a photoluminescence quantum yield of ca. 100 %, a high RISC rate of 2.57×106 s−1 and a high radiative decay rate of 1.00×107 s−1 simultaneously. With this compound as the sensitizer, a TADF‐sensitized‐fluorescent organic light‐emitting diode shows a maximum external quantum efficiency of 31.6 % with an ultrapure green Commission Internationale de L'Eclairage y coordinate value of 0.69.