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Title: Photophysical Behavior of Coumarins as a Function of Substitution and Solvent: Experimental Evidence for the Existence of a Lowest Lying 1(n,.pi.*) State
Authors: Melo, J. Sérgio Seixas de 
Becker, Ralph S. 
Maçanita, António L. 
Issue Date: Jun-1994
Publisher: American Chemical Society
Citation: The Journal of Physical Chemistry. 98:24 (1994) 6054-6058
Abstract: 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 Kin nonpolar and polar solvents in conjunction with theoretical data obtained with different methods: INDO/S-CI, CNDO/ S-CI, MNDO-CI, and AM1-CI. Theresultsshow that SI isactually n,?r* for coumarininanysolvent. Substitution with methoxy and methyl and/or chlorine and/or the increase of solvent polarity reduces the energy gap between the SI (n,**) and S2 (?r,?r*) states, promoting the mixing of these states and finally inducing inversion to SI (r,**) with trisubstitution and for the disubstituted case in dioxane:water (1:4). The presence of a lowest lying SI (n,a*) mediates a large degree of radiationless processes in the singlet mannifold.
DOI: 10.1021/j100075a002
Rights: openAccess
Appears in Collections:FCTUC Química - Artigos em Revistas Internacionais

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