Low-lying excited states and their relaxation pathways of phenothiazine

Abstract

The first two, low-lying electronic excited states of phenothiazine and their relaxation pathways have been investigated using multi-configuration self-consistent field, equation-of-motion coupled cluster and density functional theory (DFT) methods considering the def2-TZVP triple-ξ quality basis set as well as the MN12-SX exchange correlation functional in the case of DFT. The electronic configurations of the first three vertical excited states as well as the geometries of conical intersections between different excited states were discussed in details. The results show that the most feasible electronic excited state relaxation pathway is the non-radiative relaxation to the first excited state, and finally the PTZ losses its excitation via fluorescence emission. The MN12-SX DFT method gives near close geometry configurations to the MCSCF multi-reference theory proving that this method can be successfully used for computing the critical points and the relaxation channel over the potential energy hyper-surface.