DFT and MP2 calculations on new series of hydroxythioxanthones

Experimental and theoretical calculations on the molecular geometries and the vibrational spectra of a series of hydroxythioxanthones were carried out by the density functional theory (DFT/B3LYP) and MP2 methods. The geometries of molecules in the gas phase were optimized using the DFT/B3LYP and MP2 methods by 6-31+G(d,p) basis set. Based on results, one can conclude that the some isomers have a butterfly structure while the structure of some others is nearly planer. The FT-IR spectra of the hydroxythioxanthones in the solid phase were recorded. With comparison of experimental and theoretical data, vibrational analyses of these molecules were accomplished and an assignment of the normal modes corresponding to some spectral bands was proposed. The theoretical electronic absorption spectra have been calculated by using CIS method. The calculated HOMO–LUMO energies reveal charge transfer occurs within the molecule. The isotropic chemical shift computed by 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the hydroxythioxanthones, calculated using the gauge invariant atomic orbital (GIAO) method, also shows good agreement with experimental observations. The calculation showed that sulfur atom take positive charges and may be attacked by nucleophiles.