A semiclassical dynamics simulation for a long-lived excimer state of π-stacked adenines

► Excitation and deactivation of π-stacked adenines were simulated by semiclassical method. ► A long-lived excimer state with an average C2-C2′ distance of 2.2 Å was observed. ► Strong interaction leads to the formation of excimer. ► Deformation of C2 and displacement of H2′ result in the deactivation of excimer.