Oligomers of "extended viologen", p-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium), as candidates for electron-dopable molecular wires.

We report the synthesis and spectral characterization of the first five members of an oligomeric series built from alternating p-connected 1,4-benzene and 1,4-pyridinium rings, 1[n]−4[n], n = 1−5, with p-phenylene-bis-4,4‘-(1-aryl-2,6-diphenylpyridinium) (“extended viologen”) as the repeating unit. The lengths of these rodlike molecules range from 2 to 9 nm. The monomer was obtained from p-phenylene-bis-4,4‘-(2,6-diphenylpyrylium) (5) and p-phenylenediamine (6) or p-aminoacetanilide (9). Higher oligomers were synthesized by stepwise elaboration of the monomer by reactions with the appropriate bis-pyrylium (5) or pyrylium-phenylene-pyridinium (8) salts. Eight different counterions were used, and dodecamethylcarba-closo-dodecaborate was found to offer particularly favorable solubility characteristics. Ultraviolet absorption spectra of the oligomers suggest that the individual extended viologen segments interact only weakly, as a result of the strongly twisted orientation of the benzene rings that separate t...