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Oligomers of “Extended Viologen”, p-Phenylene-bis-4,4‘-(1-aryl-2,6-diphenylpyridinium), as Candidates for Electron-Dopable Molecular Wires
journal contribution
posted on 2005-01-21, 00:00 authored by Michal Valášek, Jaroslav Pecka, Jindřich, Gérard Calleja, Peter R. Craig, Josef MichlWe 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.