Arylenevinylene-based pi-conjugated polymers containing imidazolium cationic units in the main chain and their model compounds were synthesized and characterized in terms of optical and electrochemical properties. 9,9-Bisoctylfluorene, 2,5-bisdodecyloxybenzene, and 3-dodecylthiophene were introduced as arylene units with different donor characteristics to evaluate the effect on the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap energy. The UV-vis and fluorescence spectra of cationic polymers and model compounds with iodide counter anion exhibited a significant blue shift with respect to the parent neutral molecules. X-ray single crystal analysis for model compounds revealed that the effective pi-conjugation length of cationic model compounds decreased compared to the neutral model compounds by means of twisted conformation directed by CH-pi interactions between N-methyl groups of imidazolium and neighboring aryl units. The cyclic voltammetry measurement suggested the negative shift of LUMO levels by the conversion of imidazole to imidazolium, indicating the electron-accepting characteristics of cationic imidazolium unit. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1895-1906, 2011