Theoretical investigation on the fast kinetics mechanism for vibronically activated photochromism in benzopyrans. The role of the conical intersection topology in driving the mode enhanced photoproducts

The photophysics of the 2H-chromene (CF), was revisited in order to rationalize the vibronic effect, in particular the fluorescence quantum yields dependence on the excitation wavelength to the lowest singlet excited state (S1). A Full topological analysis of the potential energy surface (PES) is carried out at CIS level with CR-EOMCCSD(T) excitation energies computed at all relevant points in the PES. Particular attention is given to the topology of the conical intersection to rationalize the dynamics of the diabatic deactivation, through the seam of a conic intersection, to the ground state of the two coloured photo-product or the regeneration of the closed form.