DFT investigations of the ground and excited state geometries of the benzothiazine and benzisothiazol based anticancer drugs

Density-functional theory (DFT) is a prevailing method for predicting the geometry of organic compounds. The ground state geometries have been calculated at the B3LYP/6-31G∗∗ and PBE0/6-31G∗∗ levels of theories. The excited state geometries have been computed at time dependent DFT (TD-DFT) by using TD-B3LYP/6-31G∗∗ and TD-PBE0/6-31G∗∗ levels of theories. It has been revealed that the PBE0 functional is better than B3LYP to predict the S–O and S–C bond lengths. Both of the functionals could not reproduce the S–N bond lengths. The B3LYP is good to imitate the C–N and C–O bond lengths. The C–C and C–Cl bond lengths have been impersonated by both the functionals. Moreover, it has also been revealed that the S–N bond length elongated while the C–N bond length shortened from ground to excited state.