Highly Efficient Luminescence from a Red Thermally Activated Delayed Fluorescence Emitter with Flexible Conformation of Ancillary Groups

Abstract

AbstractRobust scaffolds were typically applied in thermally activated delayed fluorescence (TADF) molecules to suppress the non‐radiative decay, trigger the fast spin‐flipping, and enhance the light out‐coupling efficiency. Herein, we disclosed for the first time the positive effect of flexible conformation of ancillary groups on the photophysical properties of TADF emitter. The red TADF emitter Ph‐TPA with flexible conformation demonstrated small excited‐state structural distortion and low reorganization energy compared to the counterpart Mc‐TPA with a rigid macrocycle. Consequently, Ph‐TPA showed an excellent photoluminescent quantum yield (PLQY) of 92 % and a state‐of‐the‐art external quantum efficiency (EQE) of 30.6 % at 630 nm. This work could deepen our understanding of structure‐property relationships of organic luminophores and help us to rationalize the design of efficient TADF materials.