FLAVIN-PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMER IN THE PRESENCE OF MAGNESIUM PERCHLORATE

We have investigated the photosensitized monomerization of the cis,syn -cyclobutane dimer of 1,3-dimethylthymine using riboflavin tetraacetat e and a 5-deazaflavin derivative as photosensitizer. Although little m onomerization of the dimer is induced by photoexcitation of the flavin s in the absence of any additives, the flavins can function as an effi cient photosensitizer in the presence of magnesium perchlorate. Mechan istic studies involving spectroscopic, quantum-yield and flash-photoly sis measurements demonstrated that the photosensitized monomerization exclusively proceeds through electron transfer from the dimer to the t riplet flavins complexed with Mg2+. The effects of magnesium perchlora te are compared with those on the chloranil-photosensitized monomeriza tion and also with the effects of HClO4 on the flavin-photosensitized reaction.