Design, synthesis and study of the bridged and cofacially-arrayed poly-p-phenylene molecular wires
Two novel series of bridged and cofacially-arrayed poly- p -phenylenes have been designed synthesized and studied. The bridged poly-p -phenylenes have been synthesized from a readily available diacetylenic precursor utilizing three high yielding steps, and their structures were determined by 1 H/13 C NMR spectroscopy as well as X-ray crystallography. The racemization barrier between the two atropoisomers was found to be ∼12 Kcal mol-1 ; the versatility of the synthesis employed was extended to synthesis a triply bridged tetra- p -phenylene and a quadruply bridged penta-p -phenylene. The cofacially-arrayed poly-p -phenylenes have shown that the X-ray crystal structures of the neutral compounds are largely dominated by C-H--π-interactions interactions while the dicationic species display an almost perfect parallel arrangement of the cofacially-arrayed poly- p -phenylene moieties. Electrochemistry of the cofacially-arrayed poly-p -phenylenes and their model compounds consistently met the reversibility criteria. Electronic absorption spectra show that the two series are strikingly similar; however the emission spectra show that the cofacially-arrayed poly-p -phenylenes are significantly broader and bathochromically shifted in comparison to the model compounds. Electrochemical oxidation of 2,3,6,7-tetramethoxy-9,10-dimethylanthra-cene showed that it undergoes a highly reversible electrochemical oxidation ( Eox = 0.81 V vs. SCE) and forms a modestly stable cation-radical salt in solution. The X-ray crystal structure showed the presence of a dicationic homotrimer that decomposes in the spiro adduct when allowed to sit at ambient temperatures.
Matthew J Modjewski,
"Design, synthesis and study of the bridged and cofacially-arrayed poly-p-phenylene molecular wires"
(January 1, 2009).
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