title: Oligomers of "extended viologen", p-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium), as candidates for electron-dopable molecular wires.
abstract: 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 them. The UV spectrum of the monomer was interpreted by comparison with semiempirical INDO/S calculations performed at a DFT optimized geometry.
authors.affiliation: Department of Organic Chemistry, Charles University, Albertov 2030, Prague 2, Czech Republic.
authors.forename: Michal
authors.initials: M
authors.lastname: Valásek
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Pecka
authors.forename: Jindrich
authors.initials: J
authors.lastname: Jindrich
authors.forename: Gérard
authors.initials: G
authors.lastname: Calleja
authors.forename: Peter R
authors.initials: PR
authors.lastname: Craig
authors.forename: Josef
authors.initials: J
authors.lastname: Michl