The interplay between ??*/n?* excited states in gas-phase thymine: a quantum dynamical study

A quantum mechanical study of the interplay between the bright ??*(S(?)) and the dark n?*(S(n)) excited states of thymine in the gas phase is reported. TD-PBE0 calculations indicate that within a relevant region of the S(?) surface, connecting the Franck-Condon point with the planar and non-planar S(?) plateau, S(?) and S(n) are almost isoenergetic and that a S(?)->S(n) population transfer is therefore likely. This latter process has been studied by two complementary quantum dynamical approaches, a three-dimensional anharmonic (quartic) model, and a full-dimensional harmonic linear vibronic coupling model. Although providing slightly different quantitative indications, both approaches predict a very fast and effective S(?)->S(n) population transfer: already at 50 fs the S(n) state is significantly populated (20-40%) and this population persists or even increases on a longer time scale.