Acridin-9(10H)-one based thermally activated delayed fluorescence material: simultaneous optimization of RISC and radiation processes to boost luminescence efficiency

Abstract

It is strongly desired for the thermally activated delayed fluorescence (TADF) compounds to possess high rate constant of radiation (KR) and high rate constant of reverse intersystem crossing (KRISC) simultaneously. A novel TADF compound, 3,6-di(10H-phenoxazin-10-yl)-10-phenylacridin-9(10H)-one (3,6-DPXZ-AD), is designed by attaching phenoxazine as electron donor at the 3,6-sites of acridin-9(10H)-one as acceptor. The unique sp2-hybridization of nitrogen atom of acridone ring leads to a quasi-equatorial conformer and high molecular rigidity of 3,6-DPXZ-AD, which suppress conformation relaxation and finally generate high KR of 1.4×107 s-1. The phosphorescence of 3,6-DPXZ-AD with unexpected higher energy than its fluorescence is proved to originate from the intermolecular through-space charge transfer state (TSCT) and the locally excited triplet states (3LE). Due to multichannel RISC process from the TSCT and 3LE states to the 1CT state, a high KRISC of 1.1×106 s−1 is realized simultaneously. 3,6-DPXZ-AD reveals a short TADF lifetime of 1.6 ms and a high fluorescence quantum yield of 94.9%. The yellow organic light-emitting diode with 3,6-DPXZ-AD as doped emitter exhibits excellent performance with low turn-on voltage of 2.2 V, an external quantum efficiency of 30.6% and a power efficiency of 109.9 lm W-1, being among the best values ever reported for acridone based materials.