Vibrational spectra and first-order molecular hyperpolarizabilities of p-hydroxybenzaldehyde dimer

Abstract

Single crystals of p-hydroxybenzaldehyde (PHBA) were grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier transform IR spectroscopy. The density functional theoretical (DFT) computations were also performed at the B3LYP/6-311++G(d,p) level to derive the equilibrium geometry, vibrational wavenumbers and intensities. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. The various intramolecular interactions that is responsible for the stabilization of the molecule was revealed by natural bond orbital analysis. Vibrational analysis based on the NIR-FT-Raman, FT-IR and computed spectrum reveals that the CH in-plane bending of the aldehyde group interacts with its stretching mode via Fermi Resonance and evidence for intermolecular interaction can be well identified as two CH bands in IR spectra at 2740 and 2804 cm −1 aldehyde group of the p-hydroxybenzaldehyde dimer. The red shift of the O–H stretching wavenumber is due to the formation of strong O–H⋯O hydrogen bonds by hyperconjugation between the carbonyl oxygen lone electron pairs and the O–H σ * anti-bonding orbitals.