Reactivity of some S-bridge containing diphenyl derivatives (sulfides, sulfoxides, sulfones) towards ortho-positronium atoms in dimethylsulfoxide solution

The effect of changes in the chemical structure of organic sulfur compounds on their reactivity towards an ortho-positronium (o-Ps) atom was investigated by positron annihilation lifetime spectroscopy in dimethylsulfoxide solutions. S-bridge containing molecules with very similar structural frameworks were selected as model systems, such as, diphenyl sulfide, sulfoxide and sulfone, and their derivatives. The effect of the type of the S-bridge on the reactivity increased in the order of S < SO < SO2 in all groups of the compounds with similar substituents on their phenyl groups. The same trend was observed for the calculated excess positive charge on the sulfur atoms and the LUMO energies of the molecules too. As it was expected, electron-withdrawing substituents on the aromatic rings increased both the reactivity and the negative values of the LUMO energy of the molecules (COOH < NO2) whereas those with electron-donating character (CH3O) showed the opposite effect.