Giri Rajesh
Department of Physics and Electronics, Rajdhani College, University of Delhi, Ring Road, Raja Garden, New Delhi 110015, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2004 Mar;60(4):757-63. doi: 10.1016/S1386-1425(03)00287-7.
Fluorescence quenching of 4-methyl-7-methoxy coumarin (1) and 4-methyl-5-ethoxy-7-methoxy coumarin (2) in aqueous solutions have been studied at different concentrations of halide ions (Cl-, Br-, I-), at room temperature approximately 20 degrees C. It is observed that the fluorescence intensity of both the coumarin compounds (1 and 2) decrease with increase in the concentration of Br- and I- ions but remains almost constant in case of Cl- ion. It is observed that the quenching due to halide ions proceeds via both a diffusional and static quenching processes. The rate constants for diffusional as well as static component of quenching process have been calculated using modified Stern-Volmer relation. It is further observed, that I- ion has very high quenching ability than Br- ion and Cl) ion almost behaves as a non-quencher. It is explained in terms of the sphere of action model by showing that the value of radius of sphere of action of the halide quencher is greater than the sum of the radii of the respective coumarin and quencher. Further, pattern of the quenching ability of the halide quenchers is found to be as I- > Br- > Cl- and interestingly this is in the same order as of their ionization energy. Finally, the present quenching process has been attributed to the electron transfer resulting between colliding species.
在室温约20摄氏度下，研究了4-甲基-7-甲氧基香豆素（1）和4-甲基-5-乙氧基-7-甲氧基香豆素（2）在不同浓度卤离子（Cl-、Br-、I-）水溶液中的荧光猝灭情况。观察到两种香豆素化合物（1和2）的荧光强度均随Br-和I-离子浓度的增加而降低，但在Cl-离子存在的情况下几乎保持不变。观察到卤离子引起的猝灭通过扩散猝灭和静态猝灭过程进行。使用修正的斯特恩-沃尔默关系式计算了猝灭过程的扩散和静态成分的速率常数。进一步观察到，I-离子的猝灭能力比Br-离子高得多，而Cl-离子几乎表现为非猝灭剂。通过表明卤化物猝灭剂的作用球半径值大于相应香豆素和猝灭剂半径之和，用作用球模型对此进行了解释。此外，发现卤化物猝灭剂的猝灭能力模式为I-＞Br-＞Cl-，有趣的是，这与它们的电离能顺序相同。最后，目前的猝灭过程归因于碰撞物种之间的电子转移。
