Radical cations and dications of bis[1]benzothieno[1,4]thiazine isomers

Bis[1]benzothieno[1,4]thiazines (BBTT) are particularly electron-rich S,N-heteropentacenes and their radical cations and dications can be relevant intermediates in charge transport materials. All three regioisomers of N-p-fluorophenyl-BBTT (syn–syn, syn–anti, and anti–anti) were studied. A reliable preparation of radical cations and dications using antimony pentachloride as an oxidant gives deeply colored salts. The electronic structure of the radical cations was assessed by EPR spectroscopy, whereas dicationic structures were characterized by NMR spectroscopy. In addition, a deeper insight into the electronic structure was experimentally and computationally obtained by UV/Vis spectroscopy as well as UV/Vis spectroelectrochemistry and DFT and TDDFT calculations. BBTTs can be considered as highly polarizable donor π-systems with significant charge transfer contributions in neutral, cationic and dicationic state.