Azo−Hydrazone Tautomerism in Protonated Aminoazobenzenes: Resonance Raman Spectroscopy and Quantum-Chemical Calculations
Citations Over TimeTop 10% of 2008 papers
Abstract
The protonation effect on the vibrational and electronic spectra of 4-aminoazobenzene and 4-(dimethylamino)azobenzene was investigated by resonance Raman spectroscopy, and the results were discussed on the basis of quantum-chemical calculations. Although this class of molecular systems has been investigated in the past concerning the azo-hydrazone tautomerism, the present work is the first to use CASSCF/CASPT2 calculations to unveil the structure of both tautomers as well the nature of the molecular orbitals involved in chromophoric moieties responsible for the resonance Raman enhancement patterns. More specifically both the resonance Raman and theoretical results show clearly that in the neutral species, the charge transfer transition involves mainly the azo moiety, whereas in the protonated forms there is a great difference, depending on the tautomer. In fact, for the azo tautomer the transition is similar to that observed in the corresponding neutral species, whereas in the hydrazone tautomer such a transition is much more delocalized due to the contribution of the quinoid structure. The characterization of protonated species and the understanding of the tautomerization mechanism are crucial for controlling molecular properties depending on the polarity and pH of the medium.
Related Papers
- → Substituents Effects on the Azo-Hydrazone Tautomerism of 4-Arylazo-2,6-di-t-butylphenols(1971)9 cited
- → Nuclear Magnetic Resonance Investigations of the Azo-Hydrazone Tautomerism of Azoreactive Dye Chromophores(1997)10 cited
- Azo-hydrazone tautomerism of azo dyes(2015)
- → Studies on the Tautomerism of 2-Anilinopyridine and Related Heterocycles. II. 2-Anilino-5-nitropyridine and 2-Anilinopyrimidine(1980)9 cited
- → Nuclear Magnetic Resonance Investigations of the Azo–Hydrazone Tautomerism of Azoreactive Dye Chromophores(1997)