Synthesis and properties of oligothiophene cation radical salts

Oligothiophene cation radical salts were first prepared by the electrochemical oxidation method employing large-sized anions PF6−, AsF6, TaF6, BF4 and GaCl4. Several large-sized anions (AsF6, TaF6 and GaCl4) gave black-needle crystalline salts. All the salts showed semiconductive behavior with the electrical conductivities of 10−4–10−6 S/cm. Electrical conductivity and spectroscopic measurements on the cation radical salts have suggested that oligothiophene moiety in the present salts is highly oxidized, as in oligothiophene doped with nitrosyl salt.