Rotational dynamics of coumarins: An experimental test of dielectric friction theories

被引:68
作者
Dutt, GB [1 ]
Raman, S
机构
[1] Bhabha Atom Res Ctr, Div Radiat Chem & Chem Dynam, Bombay 400085, Maharashtra, India
[2] Univ Bonn, Lehrstuhl Theoret Chem, D-53115 Bonn, Germany
关键词
D O I
10.1063/1.1357797
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Rotational dynamics of three structurally similar coumarins; coumarin 6, coumarin 7, and coumarin 30 has been studied using a steady-state fluorescence depolarization technique. The idea is to understand how the friction experienced by a polar solute in a polar solvent depends on its dipole moment. Ab initio molecular orbital methods have been used to calculate the ground and excited state dipole moments. Although these coumarins are structurally similar their excited state dipole moments are quite different. Because of their similarity in shape and size they experience almost identical friction in alkanes, which is purely mechanical. However, in alcohols, the observed reorientation times do not follow the trend predicted by the dielectric friction theories of Nee-Zwanzig and van der Zwan-Hynes, based on their dipole moment values. Plausible reasons for the observed trend are discussed. (C) 2001 American Institute of Physics.
引用
收藏
页码:6702 / 6713
页数:12
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