Department of Physical Chemistry, University of Geneva, 30 Quai Ernest-Ansermet, 1211, Genève 4, Switzerland.
J Am Chem Soc. 2012 Jul 18;134(28):11396-9. doi: 10.1021/ja3049095. Epub 2012 Jul 5.
The effect of viscosity on the bimolecular electron transfer quenching of a series of coumarins by N,N-dimethylaniline was investigated using steady-state and time-resolved fluorescence spectroscopy. The data reveal that the static and transient stages of the quenching become dominant as viscosity increases. When extracting the quenching rate constants using a simple Stern-Volmer analysis, a decrease of the rate constant with increasing driving force is observed above ~2 cP. However, this apparent Marcus inverted region, already reported several times with the same system in micelles and room temperature ionic liquids, totally vanishes when analyzing the data with a model accounting for the static and transient stages of the quenching. It appears that the apparent Marcus inverted region arises from the neglect of these quenching regimes together with the use of fluorophores with different excited-state lifetimes.
采用稳态和时间分辨荧光光谱法研究了粘度对一系列香豆素与 N,N-二甲基苯胺的双分子电子转移猝灭的影响。数据表明，猝灭的静态和瞬态阶段随着粘度的增加而占主导地位。当使用简单的 Stern-Volmer 分析提取猝灭速率常数时，在 ~2 cP 以上观察到速率常数随驱动力的增加而减小。然而，当用一个考虑猝灭的静态和瞬态阶段的模型分析数据时，已经在胶束和室温离子液体中用相同的系统多次报道的这种明显的马库斯反转区完全消失。似乎表观马库斯反转区是由于忽略了这些猝灭机制以及使用具有不同激发态寿命的荧光团所致。
