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https://hdl.handle.net/10316/10307
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. | URI: | https://hdl.handle.net/10316/10307 | DOI: | 10.1021/j100075a002 | Rights: | openAccess |
Appears in Collections: | FCTUC Química - Artigos em Revistas Internacionais |
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Photophysical Behavior of Coumarins as a Function of Substitution.pdf | 575.97 kB | Adobe PDF | View/Open |
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