Molecular engineering by σ-linkers enables delayed fluorescence emitters for high-efficiency sky-blue solution-processed OLEDs

Abstract

Two novel thermally activated delayed fluorescence (TADF) emitters, namely Me2AcBO and F2AcBO, based on the 9,9-dimethrylacridine donor and a rigid oxygen-bridged cyclized boron acceptor, were designed and synthesized for highly efficient blue solution-processed organic light-emitting diodes (OLEDs). Me2AcBO and F2AcBO feature a twin structure derived by coupling two individual TADF monomers through non-conjugated linkers. The two new emitters exhibit 3D molecular structures, excellent thermal/morphological properties, high photoluminescence quantum yields over 97%, and high reverse intersystem crossing rates on the order of 106 s−1, which greatly benefit the high device efficiency. Solution-processed sky-blue TADF OLEDs based on Me2AcBO and F2AcBO achieved the maximum external quantum efficiency of 11.0% and 10.9%, respectively, with Commission Internationale de L’Eclairage (CIE) coordinates of (0.14, 0.25). Interestingly, relatively low efficiency roll-offs of 33% and 34% at the luminance of 1000 cd/m2 were demonstrated for Me2AcBO and F2AcBO based devices, respectively. This study presents a novel strategy to realize highly efficient sky-blue TADF emitters for solution-processed OLEDs.