| A new class of vinylene 4,4′-bipyridinium salts, also known as viologens, have been synthesized and their electronic and optical properties studied.; The conjugated vinylene bis(pyridinium)s, 1,4-bis(2-(1′ -methyl-4,4′-bipyridinium)ethenyl)arylene tetratriflate, where the arylene group was benzene or biphenyl, were prepared using a Knoevenagel-type condensation reaction in overall yields of ???%. Dihydroxy intermediates were prepared in high yield by deprotonation of 1-methyl-4-(4-pyridyl)pyridinium iodide with 1,8-diazabicyclo[5.4.0]undec-7-ene followed by condensation with the appropriate aromatic aldehyde. The reactions were not influenced by the presence of oxygen or water. The intermediates were dehydrated with benzoyl chloride and N-methylated to prepare the title compounds. The monomer, 1,1 ′-bis(2-phenylethenyl)-4,4′-bipyridinium hexafluorophosphate, was prepared in a 3% overall yield from 1,1′ -dimethylviologen. The deprotonation of 1,1′-dialkylviologens was extremely sensitive to oxygen and water, the presence of which caused only partial demethylation of the starting viologen to occur.; The reduction potentials of these compounds were studied using cyclic voltammetry and square-wave voltammetry. The two bis(pyridinium)s showed three reduction couples. The first, attributed to a two-electron reduction, was around −670 mV (Fc/Fc+) followed by two one-electron reductions at −1000 and −1130 mV, respectively. The monomeric 1,1′-bis(phenylethenyl)viologen showed three, one-electron reductions at −620, −900, and −1230mV, the first was quasi-reversible. A film was deposited on the electrode upon reduction of these compounds.; The fully oxidized vinylene viologens had very low energy absorptions between 295–414nm in solution, unprecedented for a viologen. Reduction of the viologens resulted in very broad absorptions across the visible spectrum. All three vinylene derivatives were fluorescent in solution and the solid state. In solution, the emission maxima were between 600 and 640 nm.; EPR spectra showed a single unresolved peak superimposed upon a broad peak. The narrow peak had a width of approximately 30G, a value expected for an asymmetric 1-methyl-1′-arylviologen. The broad peak, with a width of 220 nm, was attributed to aggregates of the reduced viologens.; Also reported are attempts to prepare 2,6- and 4,8-dialkylatedbenzo[1,2-b:4,5-b ′]bisthiazoles, -thiophenes, and -furans. The synthesis and characterization of poly(3-octylfuran)s is also presented. |
