Radical cation salts of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene: characteristic crystal structures and properties

A series of radical cation salts of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT), which has been known as a high-mobility p-type organic semiconductor, prepared by the electrocrystallization method, were characterized. In sharp contrast to the neutral DNTT in the solid state, which is characterized as a two-dimensional herringbone structure, all the radical cation salts of DNTT have a one-dimensional π-stacking structure of DNTT molecules, which are somewhat similar to those of the radical cation salts of [1]benzothieno[3,2-b][1]benzothiophene (BTBT), a lower homologue of DNTT. However, the electrical conductivities of the DNTT salts were far lower than those of the BTBT salts. The low conductivities of the DNTT salts were rationalized by the non-uniform columnar structure of the DNTT molecules with higher oxidation states than those of the BTBT salts. Such marked differences in conductivity could be boiled down to the π-extended molecular structure of DNTT, which can stabilize a higher oxidation state at the molecular level than that of BTBT and can create characteristic channel structures filled by counter anions and solvent molecules.