An electrochromic diquat-quaterthiophene alternating copolymer: A polythiophene with a viologen-like moiety in the main chain

A bis-bithiophenyl derivative of diquat, 3,10-bis(2,2′-bithiophene-5-yl)-6,7-dihydropyrido[1,2-a:2′,1′-c]pyrazinodiynium hexafluorophosphate (bt2dq), was synthesized by quaternization of 5,5″-bis(2,2′-bithiophene-5-yl)-2,2′-bipyridine with 1,2-dibromoethane. Its UV–vis absorption spectrum is explained by TD-DFT calculations. It shows the electrochemical properties characteristic for bipyridinium salts (viologens and diquats) and can be electropolymerized to form a conjugated polymer composed of alternating quaterthiophene and diquat blocks. The polymer has been characterised by cyclic voltammetry and UV–vis spectroelectrochemistry: it can be reversibly oxidized, with spectral signs of p-doping of the oligothiophene blocks, and reversibly reduced, with formation of viologen-like cation radicals, which dimerize or form π-stacks.

► Polymerizable bis(bithiophenyl) derivative of diquat (bipirydynium) is described.
► The polymer is comprised of quaterthiophene and diquat blocks and is the first conjugated polymer with diquat or viologen in the main chain.
► Its properties were studied by cyclic voltammetry and UV–vis spectroelectrochemistry.
► The polymer can be reversibly oxidized and reduced; it combines the redox properties of diquats/viologens and polythiophenes.