A simple and efficient photochemical process for in-situ fabrication of oligothiophene and polythiophene thin films and patterns is demonstrated. The process involves vapor deposition of monomeric precursor molecules, 2,5-diiodothiophene on a substrate followed by photodissociation of the C-I bond to produce monomer radicals that further react in the condensed phase to produce oligothiophene and polythiophene. The thienyl molecular structure of the precursor is preserved during the photochemical process, providing good pi conjugation of the produced polymer. Alkyl and cross-linking defects are negligible in the produced film. The direct conversion of the adsorbed monomer to the conjugated polymer allows easy fabrication of thin films and micro-patterns of polythiophene. (c) 2005 Elsevier B.V. All rights reserved.