Property study of triplet emitters based on selenophenol-substituted phenothiazine derivatives

In this article, we designed and synthesized ACN-PTZ and ACN-Se-PTZ by introducing phenylacetonitrile and selenophenol groups to the phenothiazine (PTZ) structure aiming to enhance spin-orbit coupling (SOC) for room-temperature phosphorescence. Because of the introduction of the donor-acceptor (D-A) structure, the luminous efficiency of ACN-PTZ increased by two times compared with that of PTZ. ACN-Se-PTZ showed obvious fluorescence quenching after introducing selenophenol; its photoluminescence quantum yield was significantly lower than those of PTZ and ACN-PTZ. In addition, the long lifetimes of ACN-Se-PTZ in solution at low temperature (77 K) and room temperature are 269.93 ms and 12.17 μs, respectively, which were higher than those of ACN-PTZ (138.19 ms and 11.73 μs). Selenophene with a heavy atom effect substituted to the benzene ring of phenothiazine acted as an electron donor and quenched the fluorescence due to the promoted intersystem crossing (ISC) process. Various photophysical test results show that the introduced selenophene group destroyed the intramolecular charge transfer of the phenothiazine precursor, resulting in only localized excited state transitions in ACN-Se-PTZ.