Exploring Efficient Purely Organic Room‐Temperature Phosphorescence Materials Based on the Heavy‐Atom Effect of Thioxanthone

Abstract Purely organic roomtemperature phosphorescence (RTP) materials have aroused great interest in the organic light‐emitting diode (OLED) area, benefiting from their good capacity of harvesting both singlet and triplet excitons, but most of them can only provide inferior electroluminescence efficiencies. In this work, by leveraging the enhanced spin‐orbit coupling (SOC) induced by the heavy atom effect, two new RTP materials (TXT‐DPA and TXT‐ t DPA) consisting of thioxanthone acceptor and diphenylamine‐based donors are designed and synthesized. Their crystal structures, thermal stability, energy levels, electronic structures, photophysical properties, and electroluminescence behaviors are thoroughly investigated. They behave dual emission features of thermally activated delayed fluorescence (TADF) and RTP with short lifetimes at microsecond time scale. In contrast, the analogous molecules containing xanthone acceptor (XT‐DPA and XT‐ t DPA) mainly exhibit TADF feature. Taking advantage of strong emission and high exciton utilization in doped films, TXT‐DPA and TXT‐ t DPA can function as efficient emitters in OLEDs, providing maximum external quantum efficiencies of 17.7% and 27.3%, respectively. The insights gained in this work are conducive to exploring efficient RTP materials for the application in high‐performance OLEDs.