Living organisms exposed to sunlight are constantly challenged by the formation of UV-induced lesions in DNA, which induce cell death and cause mutations. UVirradiation of TpT and TpC sequences leads to the formation of two primary lesions, namely cyclobutane-pyrimidine dimers (CPD)and lesions, as depicted in Scheme 1. These lesions possess an additional absorption at lmax=320 nm and rearrange to give Dewar valence isomers.