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International Journal of Photoenergy
Volume 2006 (2006), Article ID 35610, 6 pages
http://dx.doi.org/10.1155/IJP/2006/35610

Excited-state relaxation of some aminoquinolines

Chemistry Department, M. V. Lomonosov Moscow State University, Vorob'evy Gory, Moscow 119992, Russia

Received 25 April 2005; Revised 6 July 2005; Accepted 13 July 2005

Copyright © 2006 M. N. Khimich and B. M. Uzhinov. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The absorption and fluorescence spectra, fluorescence quantum yields and lifetimes, and fluorescence rate constants (kf) of 2-amino-3-(2-benzoxazolyl)quinoline (I), 2-amino-3-(2-benzothiazolyl)quinoline (II), 2-amino-3-(2-methoxybenzothiazolyl)-quinoline (III), 2-amino-3-(2-benzothiazolyl)benzoquinoline (IV) at different temperatures have been measured. The shortwavelength shift of fluorescence spectra of compounds studied (23–49 nm in ethanol) as the temperature decreases (the solvent viscosity increases) points out that the excited-state relaxation process takes place. The rate of this process depends essentially on the solvent viscosity, but not the solvent polarity. The essential increasing of fluorescence rate constant kf (up to about 7 times) as the solvent viscosity increases proves the existence of excited-state structural relaxation consisting in the mutual internal rotation of molecular fragments of aminoquinolines studied, followed by the solvent orientational relaxation.