LAUSR

Abstract The spectroscopic properties of 4-(2-chlorophenyl)-2-ethyl-9-methyl-6H-thieno [3,2- f ] [1,2,4] triazolo [4,3- a ] [1,4] diazepine were investigated in the present study using FT-IR and FT-Raman techniques. The results obtained were compared with quantum mechanical methods, as it serves as an important tool in interpreting and predicting vibrational spectra. The optimized molecular geometry, the vibrational wavenumbers, the infrared intensities and Raman scattering were calculated using density functional theory B3LYP method with 6–311++g (d,p) basis set. All the experimental results were in line with the theoretical data. The molecular electrostatic potential (MEP) and HOMO LUMO energies of the title compound were accounted. The results indicated that the title compound has a lower softness value (0.27) and high electrophilicity index (4.98) hence describing its biological activity. Further, natural bond orbital was also analyzed as part of the work. Fukui functions were calculated in order to explain the chemical selectivity or the reactivity site in 4-(2-chlorophenyl)-2-ethyl-9-methyl-6H-thieno [3,2- f ] [1,2,4] triazolo [4,3- a ] [1,4] diazepine. The thermodynamic properties of the title compound were closely examined at different temperatures. It revealed the correlations between heat capacity ( C ), entropy ( S ) and enthalpy changes ( H ) with temperatures. The paper further explains that the title compound can act as good antidepressant through molecular docking studies.