Ring sulfonation of a poly(thienothiophene) produces a stable, low-bandgap (< 1.2 eV), water-processable, intrinsically conductive polymer. The optical properties of the polymer can be easily modified by varying the sulfonation level and optical-bandgap tuning can also be achieved through the use of a polycation. When used as the polyanion in layer-by-layer-assembled films with polyethyleneimine, the optical absorption properties and intensity remain unchanged for seventeen months. Stability combined with an absorption maximum located within the range for peak solar flux could render these polymers as potential dyes for solar-energy conversion applications.