| Abstract
| - The deprotonation of the push−pull molecule 4-hydroxy-4‘-nitroazobenzene leads to a substantial variationin the charge distribution over the donor and acceptor moieties in the D-π-azo-π-A system. The extra chargestabilizes the excited state, leading to a drastic red shift of ca. 100 nm in the λmax of the electronic transitionand consequently causes significant changes in the resonance Raman enhancement profiles. In the neutralspecies the chromophore involves several modes, as ν(CN), ν(NN), and νs(NO2), while in the anion theselective enhancement of the νs(NO2) and ν(CO-) modes indicates a greater geometric variation of the NO2and CO- moieties in the resonant excited electronic state. The interpretation of the electronic transitions andthe vibrational assignment are supported by quantum-mechanical calculations, allowing a consistent analysisof the enhancement patterns observed in the resonance Raman spectra.
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