Intramolecular Photodimerization of Bisthymine Compounds

The cyclic bisthymine compounds were prepared in order to obtain the complete reversible photodimerization system. The photodimerizations of the bisthymine compound and the cyclic bisthymine compound in dilute solution were very fast by irradiation of UV light at 280nm, and the photodimers gave the original thymine compounds effectively by irradiation at 240nm. The GPC and the NMR data indicated that the photodimer obtained was the cis-syn isomer which was active for the photosplitting reaction. In thin solid film, however, the conversion and the rate of the photodimerization were lower than the results in dilute solution. The reason for this finding was concluded to be the presence of conformer which was inactive for the photodimerization.