Dynamics of laser-excited stacked adenines: semiclassical simulations

The nonradiative decay of a π-stacked pair of adenine molecules, following laser excitation, was studied by semiclassical dynamics simulations. Two deactivation pathways were characterized. One pathway involves an ultrafast internal conversion within ~600 fs induced by an out-of-plane vibration of the H atom and deformation of the pyrimidine ring at the C(2) site. A slower process (~2400 fs) involves covalent bond formation between the stacked molecules, which lowers the excimer state energy and inhibits the deformation of the pyrimidine ring; the decay is also induced by an out-of-plane vibration of the H atom at the C(2) site of the pyrimidine ring.