Pure\nroom temperature phosphorescence emission in\nnondoped OLEDs: adjustable oxidation states and excited-state modulation

Purely\norganic room temperature phosphorescence (RTP) materials\nare a new kind of triplet emitter, which can harvest both singlet\nand triplet excitons in theory, thus showing great application potential\nfor organic light-emitting diodes (OLEDs). However, nondoped OLEDs\nbased on RTP emitters have been rarely explored owing to challenges\nin realizing efficient phosphorescence in single-component systems.\nHerein, three donor–acceptor-type luminogens were designed\nand synthesized in which phenothiazine, with different oxidation degrees,\nacted as the electron donor and acetophenone as the acceptor. The\nadjustable oxidation states of phenothiazine enabled the modulation\nof excited states, facilitating the transition from dual RTP and thermally\nactivated delayed fluorescence emissions to pure RTP. A nondoped OLED\ndevice was then fabricated based on the pure RTP emitter, achieving\na high exciton utilization efficiency of 86%, clearly demonstrating\nthe enhancement of electroluminescence performance through RTP properties.