28045-90-1Relevant articles and documents
Photophysical Behavior of Coumarins as a Function of Substitution and Solvent: Experimental Evidence for the Existence of a Lowest Lying 1(n,?*) State
Melo, J. Sergio Seixas de,Becker, Ralph S.,Macanita, Antonio L.
, p. 6054 - 6058 (1994)
The nature of the lowest excited state for coumarin and some derivatives was investigated using steady-state and time-resolved fluorescence data at room temperature, as well as fluorescence anisotropy at 77 K in nonpolar and polar solvents in conjuction with theoretical data obtained with different methods: INDO/S-CI, CNDO/S-CI, MNDO-CI, and AM1-CI.The results show that S1 is actually n,?* for coumarin in any solvent.Substitution with methoxy and methyl and/or chlorine and/or the increase of solvent polarity reduces the energy gap between the S1 (n,?*) and S2 (n,?*) states, promoting the mixing of these states and finally inducing inversion to S1 (?,?*) with trisubstitution and for the disubstituted case in dioxane:water (1:4).The presence of a lowest lying S1 (n,?*) mediates a large degree of radiationless processes in the singlet mannifold.
