A triplet mechanism for the formation of cyclobutane pyrimidine dimers in UV-irradiated DNA

The reaction pathways for the photochemical formation of cyclobutane thymine dimers in DNA are explored using hybrid density functional theory techniques. The findings conclude that the thymine-thymine [2 + 2] cycloaddition displays favorable energy barriers and reaction energies in both the triplet and the singlet excited states, thus providing a rationale for the faster cycloreaction observed in the singlet excited states than in the triplet excited states.