Triplet excited states in DNA have been proven to provide a mechanism to thymine dimerization, a photochemical reaction that leads to carcinogenic lesions. However, and in contrast to singlet states, our knowledge about triplet states in DNA is largely limited to the properties of monomeric bases. Thus, the mobility and degree of delocalization of triplet excitons in DNA remains unclear. In a recent study published in Angewandte Chemie International Edition, we use a combination of quantum chemistry and molecular dynamics simulations to estimate the parameters needed to describe triplet exciton migration in DNA in the framework of Marcus theory. We estimate that triplet excitons in polyA–polyT DNA sequences are almost completely localized on single bases, and their migration occurs on the nanosecond timescale. Because this timescale is longer than the approximately 140 ps needed for the formation of cyclobutane thymine dimers, our results suggest that this lesion should arise on the base paris where the triplet is initially formed.
