The photophysics of pyranthione: a theoretical investigation focussing on spin-forbidden transitions Original Research Article

In this paper we present the results of a theoretical study on the electronic structure and the photophysics of low-lying singlet and triplet states of 4H-pyran-4-thione. In a first step, Russel–Saunders coupled wavefunctions and spin-independent properties were determined by means of a recently proposed combination of density functional theory and multi-reference configuration interaction methods. Spin–orbit (SO) coupling was subsequently included at the level of quasi-degenerate perturbation theory. For the evaluation of spin-dependent properties a non-empirical effective one-electron SO mean-field Hamiltonian was employed.