The preparation of a regioregular trimethylsilanyloxydecyl 3-substituted polythiophene and its conversion to the corresponding hydroxydecyl polymer, which is soluble in common organic solvents, is described both in solution and in film. The chromic behaviour of the hydroxy functionalized polymer was investigated by UV-vis spectroscopy in different solvent/non-solvent mixtures and in the solid state by exposing the polymer adsorbed on hydroxylic matrices to methanol vapours.