PREPARATION AND ELECTRICAL CONDUCTIVITIES OF OLIGOTHIOPHENE RADICAL-CATION SALTS

In order to elucidate the relationship between the conjugation length of oligothiophenes and their electrical properties, chemical oxidation of alpha-ethyl-disubstituted oligothiophene, e.g., 5,5 ''-diethyl-2,2 ':5',2 ''-terthiophene, 5,5'''-diethyl-2,2':5',2 '':5 '',2'''-quaterth iophene, and 5,5''''-diethyl-2,2':5',2 '':5 '',2''':5''',2''''-quinque thiophene, with iodine has been investigated. The resulting solids wer e identified as partially oxidized radical-cation salts containing pol yiodide ions as counter anions. The electrical conductivity of the iod ine-oxidized oligothiophenes was found to increase with increasing con jugation length; the thiophene pentamer exhibited a room-temperature c onductivity of 4 x 10(-4) S cm(-1).