Perylene diimide based organic sensitizers capable of electron generation under illumination were used to initiate gas phase photo reduction reactions on TiO2 thin and thick film surfaces. For comparison [Ru(Bpy)(3)](2+) dye sensitizers were also studied. The photo reduction Of CO2 was carried out under static conditions in the gas phase. TiO2 films were coated on hollow glass beads via a sol-gel procedure. Pt was incorporated on the films either by adding the precursor salt in the sol, Pt(in), or by wet impregnation of calcined film with an aqueous solution of the precursor salt, Pt(on). Organic sensitizers were incorporated on the films by wet impregnation of the film from an aqueous solution. Under UV illumination, the methane yields of platinized TiO2 thin films decreased in the following order: Pt(on).TiO2 > Pt(in).TiO2 > TiO2. The presence of organic sensitizers inhibited the catalytic activity of pure and platinized TiO2 thick films under UV illumination. The relative enhancement of the reaction yields in the presence of the organic sensitizer under visible light illumination depended on the presence of Pt as well as the incorporation method of Pt in the TiO2 structure. The reaction yields were better when Pt was impregnated on the TiO2 film than when Pt was incorporated in the Ti sol. On the other hand, pure or platinized TiO2 under visible light illumination was totally inactive indicating the role of the organic dye in generating catalytically active electrons under visible light. (C) 2006 Elsevier B.V. All rights reserved.