The investigation of spectroscopic and nonlinear optical properties of some azobenzene derivatives

In this study, the ground state equilibrium structures, vibrational spectra, NMR chemical shift values, electronic absorption spectra and some electronic and nonlinear optical properties of commercially obtained selected azobenzene derivatives namely, disperse red 1 acrylate, disperse red 1 methacrylate, disperse red 13 acrylate and disperse red 13 methacrylate which are linked with electron withdrawing electron donating groups on 4 and 4' positions were investigated. The ground state equilibrium structures of all compounds were determined by using B3LYP/6-311++G(d,p) method, and since we have not found any experimental data for these compounds in literature, the results were compared with a similar molecule?s which the crystal structure was examined by XRD technique. The optimized geometrical structures were used as initial parameter for all remaining computations. The vibrational spectra of compounds were recorded by experimental FT-IR technique in 4000-400 cm-1 region for solid state, and compared with calculated ones using B3LYP/6-311++G(d,p) method. The vibrational modes were assigned with the help of experimental data and total energy distribution (TED) results obtained by SQM (scaled quantum mechanics) method. The 1H and 13C NMR spectra were recorded in chloroform (CDCl3) and dimethylsulfoxide (DMSO) solutions and compared with the calculated results obtained by using GIAO (gauge-invariant atomic orbital) method. Hence, the chemical shifts of hydrogen and carbon atoms were determined, and structures of the compounds were examined and compared with similar studies in literature. The electronic absorption spectra were recorded in ethanol and methanol solutions in 200-800 nm region using a UV-Vis spectrometer at room temperature, and obtained by time dependent-density functional theory (TD-DFT) and CIS(D) (singles-doubles configuration interaction) methods. Besides, some other electronic features such as energies of highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and some other excited level molecular orbitals, electronic excitations and species, the wavelengths that excitations are occurred and dipole moments were determined in vacuum and in solutions. The nonlinear optical properties such as polarizability and first hyperpolarizability of investigated molecules and their tensorial components were calculated and compared with the results of similar investigations in the literature. As a result, it was obtained from experimental and computational results that the all molecules exist in trans conformation in the ground state, they have a strong intramolecular charge transfer and therefore, they are strong candidates to be used in nonlinear optics.