Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
Chemphyschem. 2010 Jun 21;11(9):1903-8. doi: 10.1002/cphc.201000082.
A comprehensive characterization of the electronic spectral and photophysical properties of the leuco (reduced) form of several indigo derivatives, including indigo and Tyrian Purple, with di-, tetra-, and hexa-substitution, was obtained in solution. The characterization involves absorption, fluorescence, and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields of fluorescence, phi(F) (0.46-0.04), intersystem crossing, phi(Tau) (0.013-0.034), internal conversion, phi(IC), and the corresponding lifetimes. The position and degree of substitution promote differences in the spectral and photophysical properties displayed by the investigated leuco derivatives. The phi(F) values are about two orders of magnitude higher than those previously obtained for the corresponding keto forms. Also in contrast with the behavior found for the keto forms, the S(1) approximately approximately -->T(1) intersystem crossing is an efficient route for the excited-state deactivation channel. These findings strengthen the fact that, in contrast to keto indigo where the internal conversion dominates the deactivation of the excited-state, with leuco indigo (and derivatives), the excited state deactivation involves competition between internal conversion, triplet state formation, and fluorescence. A time-resolved investigation of one of the compounds in glycerol showed the presence of a photoisomerization process.
对几种靛蓝衍生物（包括靛蓝和泰尔紫）的隐色（还原）形式的电子光谱和光物理性质进行了全面表征，这些衍生物具有二取代、四取代和六取代。表征方法包括吸收、荧光和三重态-三重态吸收光谱，以及荧光量子产率（φ（F）（0.46-0.04））、系间穿越（φ（tau）（0.013-0.034））、内转换（φ（IC））和相应寿命的定量测量。取代基的位置和程度促进了所研究的隐色衍生物显示出的光谱和光物理性质的差异。φ（F）值比以前获得的相应酮型高出两个数量级。与酮型的行为形成对比的是，S（1）~>T（1）系间穿越是激发态失活通道的有效途径。这些发现证实了一个事实，即与内部转换主导激发态失活的酮型靛蓝不同，对于隐色靛蓝（及其衍生物），激发态失活涉及内部转换、三重态形成和荧光之间的竞争。在甘油中对一种化合物的时间分辨研究表明存在光异构化过程。
