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

• Eight azo derivatives with two donors and four acceptors have been synthesized. • Characterization carried out by using 1 H, 13 C- NMR, HRMS Spectroscopies. • Both Computational and experimental IR and UV-Visible data are in good agreement. • UV-Visible and DPV studies reveal extensive solvation in polar solvents. • Upward shift in HOMO of protonated dye in DCM result in bathochromic absorption. 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 1 H-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. We present herewith a study of eight carefully designed and synthesized azo dye molecules. In this study, we have two electron withdrawing functional groups placed in the meta and para positions with respect to the azo functional group, resulting in four acceptor groups, against two donors - diphenylamine and N,N-dimethyl phenyl groups. Absorption, vibrational spectroscopy, and evaluation of HOMO-LUMO energies, are found in good agreement for both experimental and theoretical analyses. Combining Absorption and electrochemistry techniques, we found that the HOMO level increases in energy for the dyes in protonated state in nonpolar solvent like DCM while it is stabilised through solvation in polar solvents like methanol and DMF.