Abstract
The photophysical characteristics of a group of coumarins with a 3:4-fused ring system (2-substitut-ed-4,5-dioxo-l,2-dihydro-4H,5H-pyrano-[3:4-c] [1]-benzopyrans) in solutions at room temperature, in frozen ethanol matrix at 77 K, in solid phase and in PVC films are reported. The low fluorescence quan-tum yield of the compounds investigated in solution is explained as a result of internal conversion from the fluorescent S2 (ππ*) state to the lower lying S1(nπ*) state. The phosphorescence with a life time in the order of seconds is connected with intersystem crossing S1 (nπ*) -T1(ππ*). The absorption Franck Condon transitions in solid phase and in PVC matrix are only weekly batochromically shifted accord-ing to solution.
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