Photoinduced dissociation of cyclobutane thymine dimer studied by semiclassical dynamics simulation

Photoinduced dissociation of the thymine dimer is studied in a semiclassical dynamics simulation. The simulation follows excitation of an isolated thymine dimer by a 25 fs fwhm laser pulse, and finds that dissociation proceeds via an asynchronously concerted mechanism, in which the C5–C5′ bond breaks soon after application of the laser pulse, followed by cleavage of the C6–C6′ bond. The dissociation results in two thymine monomers, one in an electronically excited state and the other in the ground state. The former decays to the electronic ground state through an avoided crossing induced by deformation of the pyrimidine ring at the C5′ and C6′ sites.