Photodimerization of the crystalline esters of tetrathiafulvalenecarboxylic acids

The products from the phototransformations of crystalline 2,7-dibutoxycarbonyl-tetrathiafulvalene, 2,7-dimethoxycarbonyltetrathiafulvalene, and methoxycarbonyl-tetrathiafulvalene are photodimers, i.e., the esters of cis-4,9-bisdithiolylidene-3,5,8,10-tetrathiatricyclo(5.3.0.0/sup 2,6/)decanecarboxylic acids. 2,7-Dibutoxy-carbonyltetrathiafulvalene also gives a photodimer with a cage structure. Photodimerization is not observed in solutions. 2,6-Dibutoxycarbonyltetrathiafulvalene does not photodimerize in the crystalline state but isomerizes to the 2,7-isomer during exposure to light in solutions.