Resonance Raman spectroscopic study of bis-azo pigments

The IR, resonance Raman (RR) and electronic spectra of two bis-azo pigments, Pigment Yellow 13 and Pigment Orange 34 were interpreted in terms of hydrogen-bonded hydrazo structures. Assignments of the vibrational and electronic spectra were facilitated by ab initio calculations at the B3-LYP/DZ level. A qualitative assessment of relative RR band intensities, in conjunction with band assignments, revealed the geometric changes which occur upon electronic excitation. These are in accordance with the nature of the electronic transitions predicted by time-dependent B3-LYP/DZ calculations. Copyright (C) 2004 John Wiley Sons, Ltd.