Crystal structure, Hirshfeld surface analysis, and DFT theoretical studies of an azobenzene derivative from powder X-ray diffraction

Abstract

4-(phenylazo)benzoic acid is a photosensitive trans-azobenzene derivative. Powder data from X-ray diffraction was utilized to identify the crystal structure of 4-(phenylazo)benzoic acid by applying the direct space parallel tempering technique and Rietveld refinement. The coplanarity of the azobenzene molecule is affected by the substituting electron-withdrawing carboxyl group. Both intramolecular C − H····O and C − H····N and intermolecular O–H····O, C–H····π(arene), and π(arene)····π(arene) interactions result in the crystal stabilization of the azobenzene derivative. Intermolecular O–H····O interactions combined with C − H····π (arene) and π(arene)····π(arene) interactions form a 2D zigzag framework parallel to the (001) plane. The Hirshfeld surface, when plotted over the shape index, clearly shows the presence of π(arene)····π(arene) interactions in the compound. The FMO energy parameters are calculated from DFT computations of the compound. The time-dependent density functional theory method has been used to study the influence of electron-withdrawing para-substitution on the absorption spectrum of the azobenzene compound. Mulliken population analysis was also studied to correlate the molecular packing in the crystalline state with electronic properties. The UV spectrum of the azobenzene compound was recorded, compared with the theoretical UV spectrum, and studied to see how any solvent would influence the position of peak maxima in the experimental UV spectra. The effect of various substituents on intermolecular interactions and optoelectronic characteristics is also studied here using a few similar compounds retrieved from CSD.