DFT theoretical, spectroscopic and X-ray diffraction studies on 4-methyl-2′-hydroxy-4′-alkyloxyazobenzenes Original Research Article

Liquid crystalline 4-methyl-2′-hydroxy-4′-alkyloxyazobenzenes containing chelate O–H ⋯ N hydrogen bonds and alkyl chains with 1–12 carbon atoms were studied by using IR spectra, X-ray diffraction and DFT calculations. The results showed that in condensed phases dimeric species can be formed with antiparallel orientation of OH groups that presents an example of interaction traditionally treated as bifurcated hydrogen bonds. The experimentally determined structure of single molecules is in excellent agreement with predicted theoretically. There is also relatively good agreement with respect to dimers. The results based on IR spectra for various derivatives including parent compounds without OH groups and deuterated samples and calculations of frequencies and intensities allowed to analyse the dynamics of investigated molecules and contribution of coordinates of particular atoms to observed modes. Of particular interest were modes into which the δ(OH) and γ(OH) vibrations contributed. A minor influence of dimerization and alkyl-chain length on IR spectra was discussed.