Electronic structure and nonlinear optical properties (NLO) of 2,4-di-aryl-1,5-benzothiazepine derivatives using DFT approach

The electronic structure of and NLO of 2,4-di-aryl-1,5-benzothiazepine and some of its derivatives are investigated theoretically at the B3LYP/6-311G**level of theory. The extent of delocalization and intramolecular charge transfer are estimated and discussed in terms of natural bond orbital analysis (NBO) and second order perturbation interactions between donor and acceptor MOs. The calculated EHOMO and ELUMO energies of the studied compounds can be used to calculate the global properties; chemical hardness (η), softness (S) and electronegativity (χ). The equilibrium geometries of the studied compounds are determined, and it was found that these geometries are non plannar. The choice of these substituents aims at creating a push- pull system on the 1,5-thiazepine basic structure which pave the way to understand their nonlinear optical properties. The calculated nonlinear optical parameters (NLO); polarizability (α), anisotropy of the polarizibility (Δα) and first order hyperpolarizibility (β) of the studied compounds show promising optical properties. 3D-plots of the molecular electrostatic potential (MEP) for some selected molecules are investigated and analyzed showing the distribution of electronic density of orbitals describing the electrophilic and nucleophilic sites of the selected molecules.