Thermally activated delayed fluorescence emitter with a symmetric acceptor–donor–acceptor structure

Abstract

A thermally activated delayed fluorescence (TADF) emitter with a symmetric acceptor– donor–acceptor structure, 3,3'-(9H,9′H-[3,3′-bicarbazole]-9,9′-diyl)bis(9H-xanthen-9-one) (CzX), was developed. Theoretical calculations based on quantum chemistry revealed that the energy difference between the singlet and triplet excited states of CzX was sufficiently small to allow TADF. In addition, the symmetric acceptor–donor–acceptor structure of CzX provided a widely distributed overlap density between its lowest singlet excited state and ground state, which led to a large transition dipole moment between them. These results suggested that CzX is promising as an efficient TADF emitter. An organic light-emitting diode (OLED) containing CzX as an emitting dopant was fabricated by vacuum deposition. The OLED displayed a maximum quantum efficiency of 19.9%. Such a high external quantum efficiency resulted from efficient TADF from CzX.