DFT computational study of optical properties for bis-Schiff bases of 8-aminoquinoline derivatives and furan-2, 3-di-carbaldehyde

Optimization of nine bis-Schiff bases derived from 5-substituted-8-aminoquinoline (I) and furan-2, 3-di-carbaldehyde (II) molecules was performed using density functional theory (DFT) in B3LYP/6-311G++ (d, p) level of theory and based on the optimized structures, structural parameters, dipole moments, as well as frontier molecular orbitals of the desired bis-Schiff bases (III) were calculated. The statistical thermodynamic functions, i.e., enthalpy changes (ΔHºr = 10.21 kcalmol⁻¹) and Gibbs energy changes (ΔGºr = 12.62 kcalmol⁻¹) were obtained from the theoretical harmonic frequencies (freq keyword). Each of these imines has four geometrical isomers (ZZ, EZ, ZE, and EE), and their relative stability for III-H was studied. It was found that ZZ (III-H) is the most unstable (9.20 kcalmol⁻¹) in four isomers. To check the nonlinear optical (NLO) properties of these organic compounds the first hyperpolarizability (β_total) and average polarizability (α_ave) parameters were calculated. All of these bis-Schiff bases (III) have β_total values larger than the magnitude of the β_total value for urea (a standard molecule) and III-NO2 is the best NLO material in studied compounds. So for III-NO2, Mulliken atomic charges analysis, frontier orbitals, and molecular electrostatic potential (MEP) surfaces have been studied.