Excited-state relaxation of some aminoquinolines

• Format: Article
• Language: English
• Published: Hindawi Limited 2006-01-01
• Series: International Journal of Photoenergy
• Online Access: http://www.hindawi.com/GetArticle.aspx?doi=10.1155/IJP/2006/35610

<p>The absorption and fluorescence spectra, fluorescence quantum yields and lifetimes, and fluorescence rate constants (<mml:math> <mml:mrow> <mml:msub> <mml:mi>k</mml:mi> <mml:mi>f</mml:mi> </mml:msub> </mml:mrow> </mml:math>) of 2-amino-3-(<mml:math> <mml:msup> <mml:mn>2</mml:mn> <mml:mo>&#x2032;</mml:mo> </mml:msup> </mml:math>-benzoxazolyl)quinoline (<bold>I</bold>), 2-amino-3-(<mml:math> <mml:msup> <mml:mn>2</mml:mn> <mml:mo>&#x2032;</mml:mo> </mml:msup> </mml:math>-benzothiazolyl)quinoline (<bold>II</bold>), 2-amino-3-(<mml:math> <mml:msup> <mml:mn>2</mml:mn> <mml:mo>&#x2032;</mml:mo> </mml:msup> </mml:math>-methoxybenzothiazolyl)-quinoline (<bold>III</bold>), 2-amino-3-(<mml:math> <mml:msup> <mml:mn>2</mml:mn> <mml:mo>&#x2032;</mml:mo> </mml:msup> </mml:math>-benzothiazolyl)benzoquinoline (<bold>IV</bold>) at different temperatures have been measured. The shortwavelength shift of fluorescence spectra of compounds studied (23&#8211;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 <mml:math> <mml:mrow> <mml:msub> <mml:mi>k</mml:mi> <mml:mi>f</mml:mi> </mml:msub> </mml:mrow> </mml:math> (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.</p>