Photodimerizations of thymine derivatives having a long alkyl chain on a carbamate bond were investigated by irradiation of UV light at 280 nm in amorphous and crystalline film states. The amorphous films obtained by spin-coating from chloroform solution had higher initial rate constants for photodimerization relative to those of the crystalline films after annealing. X-Ray crystal structure analysis showed that the thymine derivatives had intermolecular hydrogen bonds that led to disadvantageous molecular orientation for the photodimerization. The photodimerization, however, is preferred in the localized layer structures of thymine units and alkyl chain.
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