Choudhury Sharmistha Dutta, Nath Sukhendu, Pal Haridas
Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India.
J Phys Chem B. 2008 Jul 3;112(26):7748-53. doi: 10.1021/jp8004019. Epub 2008 Jun 5.
The excited-state proton transfer and phototautomerization of 7-hydroxy-4-methylcoumarin (7H4MC) dye has been studied in the confined water pools of AOT reverse micelles using steady-state and time-resolved fluorescence measurements. In the "dry" reverse micelles ([water]/[AOT], w(0) = 0), only the neutral form of the dye is present both in the ground and the excited states. At higher w(0) values, three prototropic forms, namely, neutral, anionic, and tautomeric, can be identified in the excited state, although only the neutral form of the dye is present in the ground state. From steady-state fluorescence results and time-resolved area-normalized emission spectra (TRANES), it is indicated that the anionic and tautomeric forms of the dye are the excited-state reaction products and that they arise apparently independently from the excited neutral form of the dye. In bulk water, however, there is no evidence of the tautomeric species and only the anionic form is observed in the excited state. The fluorescence quenching results of the three forms of 7H4MC by the different quenchers, potassium iodide, aniline, and N, N-dimethylaniline, suggest that the distribution of 7H4MC molecules in the reverse micelles is not diverse but that the different prototropic forms arise from the same population of the excited dye in the interfacial region.
利用稳态和时间分辨荧光测量方法，在AOT反胶束的受限水池中研究了7-羟基-4-甲基香豆素（7H4MC）染料的激发态质子转移和光互变异构。在“干燥”反胶束（[水]/[AOT]，w(0)=0）中，染料的基态和激发态均仅存在中性形式。在较高的w(0)值下，尽管染料的基态仅存在中性形式，但在激发态可识别出三种质子形式，即中性、阴离子和互变异构形式。从稳态荧光结果和时间分辨面积归一化发射光谱（TRANES）表明，染料的阴离子和互变异构形式是激发态反应产物，且它们显然独立地源于染料的激发中性形式。然而，在本体水中，没有互变异构体存在的证据，且在激发态仅观察到阴离子形式。7H4MC三种形式被不同淬灭剂碘化钾、苯胺和N，N-二甲基苯胺淬灭的荧光结果表明，7H4MC分子在反胶束中的分布并非多样，而是不同的质子形式源于界面区域中相同群体的激发染料。
