Reversible photodimerization of ester derivatives of thymine having long alkyl chains in solid film

Reversible photodimerizations of eater derivatives of thymine having long a lkyl chains were studied in thin solid film. The spin coated thin film of t hymine compounds gave the photodimer under irradiation of UV light tit 280 nm, and photodimers gave original thymine compounds by UV irradiation at 24 0 nm. The rates of photodimerization in thin solid film increased with leng th of the alkyl chain, followed by decrease when the carbon number of the a lkyl chain was above 13. The behavior of photodimerization depended on the carbon number of the alkyl chains. The structures of the thymine derivative s in thin solid film were estimated from the data of differential thermal a nalysis. powder X-ray diffraction, and crystal structure of the single crys tal. The layer structures of thymines and alkyl chains were concluded to be the reason for photoactivity in thin solid film. When the carbon numbers o f the alkyl chains were 12 and 13, the photodimerizations were fast in the thin solid film, but diminished by annealing of the film. The reason for th is was the formation of the inactive micro crystals by annealing.