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 C2 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 C2 site of the pyrimidine ring.