Molecular structure, vibrational spectra and first-order hyperpolarisability analysis of 2-amino-6-nitrobenzothiazole by DFT method

Vibrational analysis of 2-amino-6-nitrobenzothiazole (2A6NBT) molecule has been carried out at room temperature using FT-IR and FT-Raman spectroscopic techniques. The equilibrium geometry, bonding features and harmonic vibrational frequencies have been investigated with the help of the density functional theory DFT method. The non-linear optical (NLO) behaviour of the examined molecule has been studied followed by the determination of the electric dipole moment , the polarisability and hyperpolarisability using HF/6-31G(d,p) method. Stability of the molecule arising from hyperconjugative interactions and charge delocalisation have been analysed using the natural bond orbital analysis. The results show that charge in electron density in the sigma(*) and (*) antibonding orbitals and second-order delocalisation energies (E-2) confirms the occurrence of intramolecular charge transfer within the molecule. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis following the scaled quantum mechanical force field methodology. The energy and oscillator strength calculated by time-dependent density functional theory complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental spectra.