Photocleavage of dimers of coumarin and 6-alkylcoumarins

The cleavage of four coumarin dimers, the syn-head-to-tail (ht) dimer of parent coumarin (syn-ht-CC1), the anti- and syn-hh dimers of 6-methylcoumarin (anti-hh-CC2 and syn-hh-CC2, respectively) and the anti-hh dimer of 6-dodecylcoumarin (anti-hh-CC3), was studied by UV-vis and IR spectroscopy and HPLC upon direct 254 nm irradiation as well as sensitized excitation. The quantum yield of dinner splitting is Phi(sp) = 0.1-0.3 in various solvents and the effects of structure and solvent polarity are small. In certain solvents some of the dimers produced CO2 along with the monomers in the splitting reaction. Electron transfer from dinners to the triplet state of sensitizers, such as benzophenone or 9,10-anthraquinone, was observed in acetonitrile. (C) 2009 Elsevier B.V. All rights reserved.