Abstract
•Synthesis of novel thiosemicarbazones by using furfural and substituted thiosemicarbazide.•Characterization of novel compounds were done through UV–Vis, IR and NMR spectroscopy.•Natural bonding orbital (NBO) properties indicated the stability of compounds.•Frontier molecular orbital energies and MEPs were calculated.•Exploration of NLO properties were performed.
A facile condensation reaction between thiosemicarbazide and furfural was accomplished to synthesize thiosemicarbazone derivatives: TMOH, FMOH, TMEH, FMEH, DCFH and DCMH with good yields as 73%, 70%, 72%,71%, 74% and 74%, respectively. They were characterized by spectroscopic techniques as UV–Vis, FT-IR, 1H and 13CNMR. Furthermore, density functional theory (DFT) analysis was performed by applying M06 level with 6–311G(d,p) basis set for geometry optimization, natural bond orbitals (NBOs), linear and nonlinear optical (NLO) and vibrational analyses. Time-dependent DFT applying M06/6–311G(d,p) level of theory was used for computing frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) and UV–Vis analyses. Experimental values of vibrational wave number and λmax values were seen in good correspondence with the DFT-based results. NBO investigation revealed that title compounds were found with prominent hyper-conjugative interactions having stabilization energies as 57.72, 62.66, 59.95, 58.54, 63.59 and 45.6 kcal/mol, respectively, which are probably the main reasons for their stability. The descending order of Egap was found as DCMH>DCFH>TMOH>TMEH>FMEH>FMOH. Therefore, FMOH, exhibiting the smallest energy gap of 4.416 eV, can be regarded as an efficiently polarized structure, possessing a high capacity for electron transfer. MEP analysis describes the involvement of various reaction sites in chemical reactivity, at different portions of spread electronic cloud over the molecule. The decrease in values of 〈α〉 for title compounds are found as DCFH>DCMH>FMOH>TMOH>FMEH>TMEH. Moreover, βtot values are found with this order DCFH>DCMH>TMOH>TMEH>FMEH>FMOH. It can be seen that DCMH exhibits a larger NLO response with 〈α〉 and βtot figured as 300.51 and 2614.07 a.u., respectively.