Polymerized Thermally Activated Delayed‐Fluorescence Small Molecules: Long‐Axis Polymerization Leads to a Nearly Concentration‐Independent Luminescence
Xue Li, Libing Yan, Shen Liu, Shumeng Wang, Jiancheng Rao, Lei Zhao, Hongkun Tian, Junqiao Ding, Lixiang Wang
Abstract
Nowadays numerous thermally activated delayed fluorescence (TADF) polymers have been developed for PLEDs to realize high device performance and tunable emission colors. However, they often possess a strong concentration dependence on their luminescence including aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE). Herein, we first report a nearly concentration-independent TADF polymer based on the strategy of polymerized TADF small molecules. It is found that when a donor-acceptor-donor (D-A-D) type TADF small molecule is polymerized through its long-axis direction, the triplet state is distributed along the polymeric backbone to effectively suppress the unwanted concentration quenching. Unlike the short-axis one with an ACQ effect, the photoluminescent quantum yield (PLQY) of the resultant long-axis polymer remains almost unchanged with the increasing doping concentration. Accordingly, a promising external quantum efficiency (EQE) up to 20 % is successfully achieved in a whole doping control window of 5-100 wt. %.