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STUDIES ON THE PHOTOTOXICITY OF COUMARIN DERIVATIVES — I. PHOTOCYCLODIMERIZATION OF 5,7‐DIMETHOXYCOUMARIN
Author(s) -
Shim Sang Chul,
Choi Kwan Yong,
Song PillSoon
Publication year - 1978
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1978.tb07560.x
Subject(s) - chemistry , photochemistry , dimer , acetonitrile , benzophenone , quantum yield , excited state , singlet state , quenching (fluorescence) , cycloaddition , triplet state , fluorescence , molecule , organic chemistry , physics , quantum mechanics , nuclear physics , catalysis
— 5,7‐DimethoxJtcoumarin (DMC) dimerizes through the C 4 ‐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.