Ionic Liquids (ILs) and poly(Ionic Liquids) (Polls) have fully tunable properties due to their different ion combinations as well as cation or anion functionalization, which results in smart materials with endless possibilities. In this study, a solid electrochromic PoIL was synthesized using a novel functionalizable and polymerizable IL (1-propyl-3-vinylimidazolium chloride bromide) and a viologen (4,4'-bipyridine) that reacted to form a monomer. Its subsequent polymerization resulted in a mechanically stable, highly ionically and electronically conductive electrochromic polyelectrolyte with a thermal decomposition temperature higher than 309 degrees C and a glass transition temperature of 13 degrees C. Spectroelectrochemical studies of the polymer deposited as a thin film over a transparent conductive substrate demonstrated a reversible redox process with reduction and oxidation potentials of - 0.45 and - 0.3 V, respectively, which was accompanied by a reversible color change from colorless (oxidized state) to purple (reduced state) with an optical contrast of 19% at 525 nm, a switching time of nearly 20 s and a coloration efficiency of 60 cm(2) C-similar to 1. Additionally, the film was repetitively switched from colorless to purple and began to lose electroactivity after approximately 4 h and 400 cycles. However, electroactivity was still observed after 16 h or 1600 cycles. Moreover, quartz crystal microbalance with dissipation monitoring indicated that the polymer charge compensation process was accompanied by a huge viscoelastic change in the film, as demonstrated by the spread of the harmonics and important changes in dissipation.