STUDIES ON THE PHOTOTOXICITY OF COUMARIN DERIVATIVES — I. PHOTOCYCLODIMERIZATION OF 5,7-DIMETHOXYCOUMARIN |
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| Authors: | Sang Chul Shim ‡ Kwan Yong Choi Pill-Soon Song† |
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| Institution: | *Department of Chemistry, The Korea Advanced Institute of Science, P.O. Box 150, Cheongyangni, Seoul, Korea;†Department of Chemistry, Texas Tech University, Lubbock, TX 79409, U.S.A. |
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| Abstract: | Abstract— 5,7-DimethoxJtcoumarin (DMC) dimerizes through the C4-photo-cycloaddition of 3,4-double bonds to form a syn head-to-tail dimer on direct irradiation ( Λ≥ 300 nm) in acetonitrile or benzene solution. The quantum yield of the photocyclodimerization in acetonitrile is 0.068 which is greater than that of coumarin.
In the presence of triplet sensitizers such as benzophenone, 5,7-dimethoxycoumarin forms an anti dimer with the quantum yield greater than 0.08. The structure of the photodimers has been elucidated by IR, UV, NMR, and mass spectrometry. The results of luminescence studies, triplet quenching and sensitization revealed that the syn head-to-tail dimer was formed via an excited singlet precursor, while the anti dimer was formed via the excited triplet state. |
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