Solution photochemistry of thymine and uracil.

With dienes as specific triplet quenchers, it has been shown that the photodimerization of thymine in acetonitrile proceeds entirely through the triplet state and the photodimerization of uracil in acetonitrile or in water proceeds in part through the triplet state. The photohydration of uracil probably does not involve the triplet state. Efficiencies of intersystem crossing of thymine and uracil in acetonitrile were determined.