Department of Chemistry, University of Coimbra, P3004-535 Coimbra, Portugal.
J Phys Chem A. 2012 Mar 22;116(11):2826-32. doi: 10.1021/jp211996f. Epub 2012 Mar 8.
The photoreaction of indigo and two other derivatives in its reduced (leuco) form was investigated by absorption and fluorescence (steady-state and time-resolved) techniques. The fluorescence quantum yield (φ(F)) dependence with the UV irradiation time was found to increase up to a value of φ(F) ≈ 0.2-0.3 (after 16 min) for indigo and φ(F) = 0.2 (at 150 min) for its derivative 4,4'-dibutoxy-7,7'-dimethoxy-5,5'-dinitroindigo (DBMNI). With a model compound, where rotation around the central C-C bond is blocked, the φ(F) value was found constant with the UV irradiation time. Time-resolved fluorescence revealed that initially the decays are fitted with a biexponential law (with 0.12 and 2.17 ns), ending with an almost monoexponential decay (2.17 ns). Quantum yields for the isomerization photoreaction (φ(R)) were also obtained for indigo and DBMNI with values of 0.9 and 0.007, respectively. The results are rationalized in terms of a photoisomerization (conversion) reaction occurring in the first excited singlet state of trans to cis forms of leuco indigo.
通过吸收和荧光（稳态和时间分辨）技术研究了靛蓝及其还原（隐色）形式的两种其他衍生物的光反应。发现荧光量子产率（φ(F)）随紫外辐照时间的依赖性增加，直到靛蓝的φ(F)≈0.2-0.3（16 分钟后）和其衍生物 4,4'-二丁氧基-7,7'-二甲氧基-5,5'-二硝基靛蓝（DBMNI）的φ(F)=0.2（约 150 分钟）。对于一个其中中央 C-C 键的旋转被阻止的模型化合物，φ(F)值被发现与紫外辐照时间无关。时间分辨荧光表明，初始衰变最初拟合为双指数定律（具有 0.12 和 2.17 ns），最终以几乎单指数衰减（~2.17 ns）结束。对于靛蓝和 DBMNI 的异构化光反应（φ(R)）也获得了量子产率，分别为 0.9 和 0.007。结果根据在隐色靛蓝的顺式到反式形式的第一激发单线态中发生的光异构化（转换）反应进行了合理化。
