Polymeric and low molecular mass azobenzenes, ferrocene derivatives and a diphthalocyanine have been deposited on silicon, principally using the Langmuir-Blodgett technique. Interference-enhanced reflectometry was used for gas sensing, with films selected to give low reflectance of green light in air. For a polysiloxane azobenzene material, reflectance changes were up to 75% on exposure to 100 ppm NO2 in air, with response and recovery times of the order of 10 s, and recovery was effectively complete. The response or deposition characteristics resulted in reduced performance for the other materials; the effect of differing deposition methods is discussed.