Prediction of molecular properties and spectroscopic profile of Riluzole with different functionals (B3LYP, M06-2X, MPWLYP): A combined theoretical and experimental study

• Vibrational analysis of Riluzole, using B3LYP, MPWLYP and M06-2X functionals.
• βtotal value at M06-2X is 19% and 16% higher in comparison to B3LYP and MPWLYP value.
• LP of electrons on O, F, S and F atoms play important role towards intramolecular charge transfer.

Comprehensive investigation of molecular geometry and electronic structure of Riluzole (6-(trifluoromethoxy)benzothiazol-2-amine) in ground as well as in the first excited state has been carried out. The stable conformers of the title compound have been determined from the 3D potential energy scan calculated at DFT/B3LYP, by varying selected dihedral angles, responsible for conformational flexibility. The most stable conformers were further optimized to obtain ground state structure using pure GGA (MPWLYP), hybrid GGA (B3LYP) and meta-hybrid GGA (M06-2X) functionals. Detailed vibrational analysis has been done for the structure obtained at B3LYP as it corresponds to the minimum energy structure. Experimental FT-IR and FT-Raman spectra were compared with theoretical spectral data. Dipole moment, polarizability, first static hyperpolarizability has been calculated at different functionals used in the study. Natural bond orbital (NBO) analysis has been done to study the stability of the compound arising from charge delocalization. UV–Vis spectrum of the title compound was also recorded and electronic properties such as frontier orbitals and band gap energies were calculated by TD-DFT approach.

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