Synthesis and Characterization of Extended Viologens for Advanced Functional Materials
Abstract: The 1,1′-dialkyl-4,4′-bipyridinium salts are commonly known as viologens. They are an important class of organic salts and appropriately called functional materials. The multitude of their applications are due to ionic conductivity, thermochromism, photochromism and electrochromism. Several extended viologens with chloride ions were synthesized by reacting the classical Zincke salt, which prepared from 4,4′-bipyridine with 2,4-dinitrochlorobenzene on heating in acetonitrile for 72 h by nucleophilic aromatic substitution, with 4-alkoxyanilines on heating in ethanol for 72 h with good yields. They were converted to tosylate salts by the metathesis reactions of the corresponding chlorides with silver tosylate on heating in water or methanol/water for 24 h with good yields. Their triflimide salts were prepared by the metatheses reactions of the corresponding tosylate salts with lithium triflimide on heating in methanol for 48 h with excellent yields. The chemical structures of these extended viologens are presented in Scheme 1. They were characterized by 1H and 13C NMR spectra as well as elemental analysis. Their solubility in different solvents, thermal properties and light-emitting properties were also explored by several experimental techniques.
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