Poly(3-methylthiophene) (P3MT) and poly(3-octylthiophene) (P3OT) are conducting polymers with interesting optoelectronic properties and a wide variety of optoelectronic applications. In this work, 3-octylthiophene was synthesized through a Grignard reactive and was analyzed by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR). The morphology of electrosynthesized P3OT and P3MT thin films was analyzed by atomic force microscopy and different film morphologies were found for different electrodeposition technique and the solution temperature. Optical absorbance spectra of the two types of films confirm the bipolaron band structure and a starting pi-pi* interband transition around 2eV. Electrochromic performance of the polymers with both liquid and polymeric electrolytes showed a high switch potential for P3OT that for P3MT films. The kinetic optical response of a P3MT electrochromic device shows a good color contrast and a capacitive current characteristic under a square electrical potential. (C) 2004 Elsevier B.V. All rights reserved.