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Characterization of the Excited States of Indigo Derivatives in their Reduced Forms
Author(s) -
Rondão Raquel,
Seixas de Melo J. Sérgio,
Voss Gundula
Publication year - 2010
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201000082
Subject(s) - intersystem crossing , photochemistry , excited state , chemistry , internal conversion , fluorescence , indigo , photoisomerization , triplet state , chromophore , absorption (acoustics) , absorption spectroscopy , isomerization , spectral line , molecule , singlet state , organic chemistry , materials science , atomic physics , optics , catalysis , physics , astronomy , composite material
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, ϕ F (0.46–0.04), intersystem crossing, ϕ T (0.013–0.034), internal conversion, ϕ 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 ϕ 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 ∼∼→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.