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Lewis‐acid‐catalyzed Photodimerization of Coumarins and N ‐methyl‐2‐quinolone
Author(s) -
Görner Helmut,
Wolff Thomas
Publication year - 2008
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.1751-1097.2008.00339.x
Subject(s) - intersystem crossing , chemistry , quantum yield , catalysis , photochemistry , yield (engineering) , dichloromethane , quenching (fluorescence) , medicinal chemistry , singlet state , fluorescence , excited state , organic chemistry , materials science , solvent , physics , quantum mechanics , nuclear physics , metallurgy
The BF 3 ‐catalyzed photodimerization of parent coumarin ( 1 ), three 6‐alkylcoumarins ( 2 – 4 ) and N ‐methyl‐2‐quinolone ( 5 ) in dichloromethane was studied by time‐resolved UV–vis spectroscopy. The lowest triplet state properties in the absence and presence of BF 3 were outlined, in particular the effect of self‐quenching which initiates dimerization. The quantum yield of intersystem crossing ( Φ isc ) of 1 – 4 increases with BF 3 concentration, approaching Φ isc = 0.3. Φ isc and the relative quantum yield of dimerization go along, thereby favoring an overall triplet mechanism in both the direct and BF 3 ‐catalyzed photodimerization. The product ratio of 5 changes strongly with the BF 3 concentration from 100% anti ‐hh for the free quinolone to 100% syn ‐ht for the 1:1 complex.