Polycondensation of 4-bis[2-(1-methylpyrrol-2-yl)vinyl]-2,5- didodecyloxybenzene and squaric acid yielded the polysquaraine SQ with two isomeric subunits-1,3-addition (zwitterionic) and 1,2-addition (diketonic) moieties-in the main chain structure. The former featured a C-O/C=O infrared (IR) absorption frequency at 1622 cm -1 ; the latter, a C=O signal at 1716 cm -1 . Traditional synthesis yielded SQ as a powder with metallic luster that could not be cast as a polymer film from solution. When the ionic liquid [Oct 3 NMe][TfO] (IL) was present in the cosolvent of BuOH and benzene (1:3), however, the resulting SQI x polymers (x = 0.01-5 wt %) did not precipitate from solution, making it possible to cast continuous free-standing films with a large area (>1 × 1 cm 2 ). A greater content of IL in the solution favored the formation of the 1,3-addition zwitterionic subunits in the SQI x polymer main chains, thereby changing the physical and optical properties of the polysquaraine, as evidenced in IR and optical absorption spectra. The features in the UV-Vis-NIR absorption spectra of SQ and SQI x were dependent on the IL concentration and the nature of the solvent. Among our synthesized SQI x polymers, SQI 0.01 and SQI 0.1 formed flexible free-standing films with metallic luster, smooth surfaces, and good semiconductivities (2.27 × 10 -5 and 4.74 × 10 -5 S/cm, respectively). X-ray diffraction patterns revealed that the presence of IL in the polymerization medium increased the SQI x interchain packing distance. SQI 0.01 and SQI 0.1 possessed thermal stabilities comparable with that of SQ. Our successful use of IL in the preparation of SQI x polymers appears to have great potential for application in ionic liquid-related organic or polymeric preparation and processing.