Methyl- and methoxy-substituted di[1,4]benzodithiio[2,3-b : 2,3-e]-pyridines as new electron donor compounds: synthesis, molecular structure, electrochemical properties, and EPR studies

Two new derivatives of di[1,4]benzodithiino[2,3-b:2,3-e]pyridine (5) tetras ubstituted with methyl (7) and methoxy (8) groups at the 2,3,9 and 10 posit ions have been prepared from 2,3,5,6-tetrachloropyridine, by cyclization re action with the bidentate nucleophiles, 4,5-dimethyl- and 4,5-dimethoxy-ben zene-1,2-dithiol. Cyclic voltammograms for the oxidation of both polyhetero cyclic compounds 7 and 8 in CH2Cl2 exhibit two consecutive redox couples. T he first pairs are due to the equilibria between the initial compounds and their radical cations, while in the second couples, the electrogenerated ra dical cations are in equilibrium with the corresponding dications. Radical cations of these molecules have been generated in fluid solution, by oxidat ion of the parent compounds with thallium(III) trifluoroacetate in trifluor oacetic acid in the case of 7, and by irradiation of a CH2Cl2 solution cont aining trifluoroacetic acid (10%) in the case of 8. Bath species were analy zed by electron paramagnetic resonance (EPR). X-Ray analysis of the molecul ar structures of both 7 and 8 shows a stable chair-shaped conformation with interplanar angles between the phenyl rings and the pyridine ring of 139.9 and 141.4 degrees for 7 and 133.7 degrees for 8.