DFT and experimental study on the spectral and nonlinear optical properties of a highly conjugated imine

•The spectroscopic and NLO properties of compound HCIM were investigated.•The calculated vibrational spectra by DFT/B3LYP/6-311++G(d,p) method shows satisfactory agreement with experimental one.•The values of calculated absorption spectra in gas phase were close to them in methanol solution.•The valley configuration of open aperture Z-scan was due to electrostriction effect. In this study, (2-((1E,2E)-3-phenylallylidene) amino)-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carbonitrile) [referred from here onwards as HCIM that is a highly conjugated imine] was synthesized via a condensation reaction between cinnamaldehyde and a 2-aminothiophene derivative, and subjected to computational and experimental approaches. At first, the IR, UV–Vis spectral, and HOMO–LUMO analysis of the synthesized compound were carried out by density functional theory (DFT) at B3LYP/6-311++G(d,p) level. Secondly, experimental study on the nonlinear optical (NLO) properties (third order optical coefficients) of compound HCIM in methanol was conducted by Z-can technique. The IR results indicated that the computational and experimental of vibrational frequencies were in good agreement with each other. The calculated HOMO-LUMO gap (HLG) in gas phase and methanol is 3.14 and 3.085 eV, respectively, and this parameter was used to interpret Z-scan data’s. The values of calculated absorption spectra of the compound HCIM in gas phase were close to them in solution phase (methanol). Also, the experimental results showed that the main origin of NLO refraction is thermal lensing effect and positive nonlinear absorption is due to electrostriction effect. Electrostriction is a characteristic of organic molecules with low HOMO-LUMO energy gap about 3.1 eV, that exhibits high electrical polarizability. Finally, the results suggest that compound HCIM is advantageous for NLO applications.