Rational insertion of peripheral rigid units to construct thianthrene-based blue TADF emitters for highly efficient solution-processed OLEDs

In spite of numerous works about diphenylsulfone-based thermally activated delayed fluorescence (TADF) emitters, the strategy of inserting rigid units to the periphery to achieve blue emission are rarely reported. Herein, we introduce a novel rigid donor, the thianthrene group, we synthesized two novel blue-emitting TADF materials: DPS-2CzTE and DPS-2Cz2TE. The diphenylsulfone unit acts as the electron acceptor (A) and the carbazole derivates act as the electron donors (D), respectively. The multiple donors result in a highly twisted A-D-D’ architecture and enhanced electron-donating capabilities, which facilitate achieving a higher reverse intersystem crossing (RISC) rate and suppressed aggregation-caused quenching (ACQ) effect. By inserting rigid thianthrenes unit into the carbazole group, the intermolecular distance was increased, effectively alleviating the large red-shift of the wavelength and breaking its planarity availably. As expected, the resulting emitters exhibited a 55 nm blue-shifted emission peak compared to reported emitters (POCz-DPS and 2CzSO) which are modified by flexible units and tert-butyl carbazole units, respectively. By regulating the number of peripheral thianthrene groups, the performance of solution-processed devices based on DPS-2Cz2TE has been improved by nearly twofold compared to DPS-2CzTE, achieving maximum external quantum efficiency (EQE_max) of 9.29 %. This work demonstrates the feasibility of selecting thianthrene as rigid groups to modify TADF emitters, and provides an important reference for the design of highly efficient blue TADF emitters in solution-processed organic light-emitting diodes.