Experimental and theoretical studies of azo derivatives in terms of different donors, acceptors and position isomerism: Synthesis, characterization and a combined electronic absorption, electrochemical and DFT study

Abstract

Eight azo derivatives with two donor groups- diphenylamine and N,N-dimethylphenyl, and four acceptor groups - 3-nitrophenyl, 4-nitrophenyl, 4-phenylcarboxylic acid, and 3-phenylcarboxylic acid, were synthesized and characterized using 1H-NMR and HRMS spectroscopies. Both experimental and computational vibrational spectroscopic analyses of the derivatives have been performed. Solvatochromism in different solvent polarities has been studied, both computationally and experimentally. We have also performed electrochemical studies on the chosen dyes. From cyclic voltammetry and UV-Visible absorption spectra, the HOMO and LUMO energies of the dyes were calculated, and compared with computational results, which are found to be in fair agreement. Protonation studies of the dyes showed that the neutral and the protonated forms of the dyes absorb differently in solvents of differing polarities. This anomaly in different solvents could be explained with the help of differential pulse voltammetry experiments. Our studies show that the HOMO energy levels of the molecules are shifted upward in energy in nonpolar DCM solvent which reduces the bandgap and is responsible for the bathochromic shift in absorption. Thermal stability investigations showed that all the dyes are very well stable at least until 220 °C.