| Abstract: | Fourier transform Raman and IR as well as UV–visible spectra of the phenothiazine dye Azure A chloride, 3‐amino‐7‐(dimethylamino) phenothiazin‐5‐ium chloride were recorded and analyzed. The spectral interpretation was done following full structure optimization and vibrational wavenumber calculations based on the density functional theory (DFT) using the standard B3LYP/6‐31G(d) basis set. The N H stretching wavenumber is found to be lowered owing to intermolecular N H···S hydrogen bonding. The downshift of C H stretching wavenumber is discussed. The first hyperpolarizability of the dye is calculated. Time‐dependent density functional theory (TD‐DFT) calculations of electronic spectra were performed on the optimized structure and compared with the experimental UV–visible spectrum. The atomic net charges of the molecule reveal the M effect of the nitrogen atoms in the molecule. Stability of the molecule arising from hyperconjugative interactions leading to its nonlinearity and bioactivity, charge delocalization and mesomeric effects have been analyzed using natural bond orbital (NBO) analysis. Copyright © 2008 John Wiley & Sons, Ltd. |
