Poly(3-chlorothiophene) (PClT) was electrochemically synthesized on a nanoporous TiO(2) surface in the ionic liquid 1-butyl-3metyllimidazolium hexafluorophosphate by galvanostat method to control charge density of 93 mC cm(-2). Spectroelectrochemical analysis presented that the PClT/TiO(2) nanocomposite film had an electronic bandgap of 1.80 eV with a bordeaux color in the reduced form and a dark blue color in the oxidized form. The switching ability of the PClT/TiO(2) nanocomposite film was monitored and the percent transmittance was measured as 12% at 555 nm and 25% at 770 nm. Moreover, a PClT/TiO(2) nanocomposite film based electrochromic device was constructed and its electrochromic properties were also investigated in this paper. (c) 2008 Elsevier B.V. All rights reserved.