Efficient\nMicrowave Irradiation-Assisted Synthesis\nof Benzodioxinoquinoxaline and Its Donor-Variegated Derivatives Enabling\nLong-Lived Emission and Efficient Bipolar Charge Carrier Transport

To enhance the usually low-charge carrier mobilities\nof highly\ntwisted donor–acceptor-type compounds that exhibit thermally\nactivated delayed fluorescence, we designed a rodlike acceptor benzodioxinoquinoxaline.\nThis acceptor and two donor–acceptor–donor derivatives\nwere synthesized via microwave Buchwald–Hartwig cross-coupling\nreactions with yields of up to 91%. The compounds exhibit three different\ntypes of photoluminescence, which is well-explained by quantum chemical\ncalculations. Benzodioxinoquinoxaline shows blue fluorescence, with\na very short lifetime of 0.64 ns. Its derivatives exhibit either green\nsolid-state-enhanced thermally activated delayed fluorescence (SSE-TADF)\nor room-temperature phosphorescence (RTP) with lifetimes approaching\n7 ms. When molecularly dispersed in a polymeric host, the compounds\nshow a photoluminescence quantum yield close to 60%. The derivatives\ncontaining acridine or phenoxazine moieties exhibit bipolar charge\ntransport. At an electric field of 5.8 × 10<sup>5</sup> V/cm,\nhole and electron mobilities of the phenoxazine-containing compound\nreach 3.2 × 10<sup>–4</sup> and 1.5 × 10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively.\nAmong the studied SSE-TADF-based organic light-emitting diodes, the\ndevice containing this compound shows the highest external quantum\nefficiency of 12.3% due to the good charge-transporting and SSE-TADF\nparameters of the emitter.