Long-lived room temperature phosphorescence and short-lived ultraviolet fluorescence: Dual-emission in a hybrid [Ph3PH][BF4] salt - for multiplexed anti-counterfeiting

Room temperature phosphorescence (RTP) materials have attracted attention for applications in fundamental research and leading-edge technologies. Designing organic RTP materials remains challenging due to difficulties in triplet state population and suppressing non-radiative decay. Herein, the tetrafluoroborate triphenylphosphonium salt, [Ph 3 PH][BF 4 ] ( 1 ), exhibiting dual emission comprising ultraviolet (UVB) fluorescence with a nanosecond lifetime and cyan-green phosphorescence with a subsecond lifetime, is reported. The low-temperature crystal-to-crystal phase transition of 1 does not cause sharp changes in its optical and luminescence properties, showing atypical temperature trends. Quantum-chemical calculations confirm the proposed photophysical mechanisms. Moreover, an RTP material with tunable phosphorescence lifetime was achieved via doping 1 into polymethyl methacrylate (PMMA). This material demonstrated good performance in time-delayed information encryption and anti-counterfeiting.