Photochemistry of Thymidine as a Thin Solid Film*

Abstract— –Photochemistry of thymidine in the solid state has been investigated. Four isomers of the cyclobutane‐type thymidine dimer, two bimolecular addition products with u.v. absorbance maxima above 300 nm, (the formation of which involves the C=C and C=O groups of adjacent thymine residues) and 5‐thyminyl‐5.6 dihydrothymine (TDHT) (formed by the addition of a thyminyl radical at the C 5 position of a thymyl radical) were isolated. TDHT was found to be the major photoproduct. The results are compared with those for thymidine irradiated in the frozen state.