The oxygen sensing mechanism of a trifluoromethyl-substituted cyclometalated platinum(II) complex

Trifluoromethyl-substituted cyclometalated platinum(II) (TSCP) is a useful material for oxygen molecule detection and determination. Through quantum chemical computation, we propose a quenching mechanism to explain the nature of oxygen sensing. The luminescence mechanism of TSCP involves phosphorescent emission and the TSCP-O-2 complex internal conversion. By applying the density functional theory (DFT) method, we computed the frontier molecular orbitals and electron configurations of TSCP and the TSCP-O-2 complex. In addition, using the time-dependent density functional theory (TDDFT) method, we computed the excited energies and geometric optimization of the excited state of TSCP and the TSCP-O-2 complex. According to the computation results, the luminescence of TSCP is due to localized excitation, while that of the TSCP-O-2 complex is due to delocalized excitation. We computed the radiative and non-radiative rate constants of TSCP and the TSCP-O-2 complex and elucidated their photophysical processes. For TSCP, after excitation, first the electron jumped from the S-1 to T-1 state by intersystem crossing, and eventually back to the S-0 state by phosphorescence emission. Instead, for the TSCP-O-2 complex without spin flip, the electron jumped directly from the T-1 to T-0 state by internal conversion.