Journal
JOURNAL OF RAMAN SPECTROSCOPY
Volume 40, Issue 9, Pages 1158-1161Publisher
WILEY
DOI: 10.1002/jrs.2250
Keywords
nitroaromatics; push-pull chromophores; nonlinear optics; azobenzene; CASSCF/CASPT2
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Funding
- FAPESP
- CNPq
- CAPES
- Instituto do Milenio de Materiais Complexos II
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The dideprotonation of 4-(4-nitrophenylazo)resorcinol generates an anionic species with substantial electronic pi delocalization. As compared to the parent neutral species, the anionic first excited electronic transition, characterized as an intramolecular charge transfer (ICT) from the CO- groups to the NO2 moiety, shows a drastic red shift of ca. 200 nm in the lambda(max) in the UV-vis spectrum, leading to one of the lowest ICT energies observed (lambda(max) = 630 nm in dimethyl sulfoxide (DMSO)) in this class of push-pull molecular systems. Concomitantly, a threefold increase in the molar absorptivity (epsilon(max)) in comparison to the neutral species is observed. The resonance Raman enhancement profiles reveal that in the neutral species the chromophore involves several modes, as nu(C-N), nu(N=N), nu(C=C) and nu(s)(NO2), whereas in the dianion, there is a selective enhancement of the NO2 vibrational modes. The quantum chemical calculations of the electronic transitions and vibrational wavenumbers led to a consistent analysis of the enhancement patterns observed in the resonance Raman spectra. Copyright (C) 2009 John Wiley & Sons, Ltd.
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