A substituted polyacetylene (PA) with viologen side groups (Polymer-1) was obtained from the reaction of 4-ethynylaniline with 1-hexyl-1'-(2,4-dinitrophenyl)-4,4'-bipyridinium dihalide (Salt-1). Model compounds (Model-1 and Model-2) were synthesized by the reaction of Salt-1 with aniline and 1-(4-aminophenyl)-2-trimethylsilylacetylene, respectively. UV-vis spectra revealed that Polymer-1 had an expanded pi-conjugation system along the polymer chain: the polymer showed an onset position of absorption at a wavelength approximately 200 nm longer than the corresponding wavelengths of the model compounds. Polymer-1 received an electrochemical reduction of the viologen group within the polymer, and the electrochemical reaction was accompanied by electrochromism. (C) 2009 Elsevier Ltd. All rights reserved.