Theoretical insights on the luminescent mechanism of an efficient aggregation‐induced nondoped delayed fluorescence emitter using QM/MM method

Abstract

AbstractThermally activated delayed fluorescence (TADF) materials with an aggregation‐induced emission (AIE) mechanism have great potential for use in organic light‐emitting diodes (OLEDs). In this study, the luminescent mechanism of a novel efficient aggregation‐induced, nondoped, delayed fluorescence emitter 2‐(10H‐phenoxazin‐10‐yl)‐10‐phenyl‐10H‐phenothiazine‐5,5‐dioxide (PXZ2PTO) is theoretically studied based on first‐principles calculations. The polarizable continuum model and quantum mechanics and molecular mechanics method are used to simulate the surrounding environments for molecules in the toluene solution and the solid phase, respectively. Our results show that PXZ2PTO exhibits the superior AIE property. The nonradiative decay rate in the solid phase is two orders of magnitude lower than that in toluene, caused by the suppressed geometry changes during excitations and decay channels. Meanwhile, studies of intermolecular interactions using the dimer model indicate that PXZ2PTO possesses a special highly stereoscopic structure in the solid phase, and the electron acceptor group is almost perpendicular to the electron donor group, inducing a strong steric hindrance effect between adjacent molecules and leading to enhanced intramolecular interaction. Furthermore, the excited‐state dynamics studies show that the intersystem and reverse intersystem crossing rates of PXZ2PTO are comparable to the radiative decay rate, which indicates that PXZ2PTO is an excellent potential TADF emitter with full exciton usage. Our theoretical research gives a reasonable explanation of the experimental results and provides valuable information for designing highly efficient AIE‐TADF emitters in practical OLEDs.