Theoretical study (CC2, DFT and PCM) of charge transfer complexes between antithyroid thioamides and TCNE: electronic CT transitions.

A set of representative DFT and wavefunction based theoretical approaches have been used to study ionization potentials and, predominantly, electronic charge transfer transitions in the complexes formed between TCNE as an electron acceptor and both mono and bicyclic thioamides as donors. The mentioned thioamides are of pharmacological importance due to their efficient antithyroid activity. Within a few kcal mol(-1) we have found six stable conformers for complexes with each of benzothioamides and four conformers for each of monocyclic thioamides. Present theoretical study satisfactorily shows that there is a good correspondence between the CC2/Def2-TZVPP calculated excitation energies for complexes in vacuum supplemented by the DFT solvent shifts and experiment. Present theoretical study contributes to deeper understanding of the electronic nature of the ground and excited states of the complexes with antithyroid activity.