Spectroscopic characterization and binding interaction of heavy metal onto the surface receptor of the azobenzene: DFT and experimental approach

The azobenzene 1-arylazo-2-naphthol has been synthesized and characterized by elemental analysis, 1H NMR, IR and UV–Vis spectroscopies using both experimental and theoretical methods. The MEP, NPA and FMOs have also been performed at the DFT/B3LYP-D3 level with different solvents in order to investigate the solvent's effect. The energetic behavior of the compound has been examined in the gas phase and in solvent media using the integral equation formalism polarizable continuum model (IEF-PCM). Solvents had sligth significant effect on NPA values whereas both molecules hardness and stability decrease along with increasing of the solvent's polarity. Vibrational and absorption analysis showed no significant azo±hydrazone tautomerism. Theorically, the title molecule calculated in Acetonitrile solvent is the most reactive. The observed red shifts are explained by the large extension of the π conjugated system and the blue shifts confirm the appearance of several tautomeric forms of the studied azo-benzene which lead to a marked improvement in photochemical stability. The cation binding properties of azo benzene as absorption sensor for Cu2+, Mg2+, Ni2+ and Zn2+ cations were reported. The highest adsorption energy in both gas and liquid phase corresponds to the complexes Azoic/Ni2+ then in Azoic/Cu2+ and somewhat in Azoic/Zn2+complex. The lowest adsorption energy is given to Azoic/Mg2+ complex. After cations chemisorption on azoic molecule a bathochromic shift is observed in the optical spectra, particularly for Azoic/Ni2+ complex, which is the proof of interaction between azoic compound and mentioned cations. The electronic proprieties and the vibrational spectra can therefore be used to detect the presence of different cations and the azobenzene shows appropriate properties to constitute good cations (Ni2+ and Cu2+) sensors.