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

摘要

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.