Photophysical and electron transfer studies of a few 2,6-dimethyl-4-(alkylphenyl)pyrylium and thiopyrylium derivatives

The photoinduced electron transfer properties of pyrylium salts 1a-d and the corresponding thiopyrylium derivatives 2a-d were investigated. Electron transfer from biphenyl (BP) acid 4,4'-dimethoxystilbene to the singlet and tripler excited states of the salts led to efficient formation of the separated radical pairs. Using BP as donor, we have estimated the extinction coefficients and also the yields of the pyranyl/thiopyranyl radicals. The yields obtained were higher than those observed in the cases of similar cationic sensitizers. We have tried to correlate the radical yields to the tripler quantum yields and also to the stability of the pyranyl radicals. The high radical ion yields observed in these cases suggest that these compounds can be used as efficient sensitizers for photoinduced electron transfer reactions. (C) 1997 Elsevier Science S.A.