Chlorine gas sensing using thin films of meso-tetra(p-stearamidophenyl)porphyrin

The generation, emission and use of toxic, flammable and asphyxiant gases i s prevalent throughout all sections of industry today. Safety at work, cont rol of hazardous substances, and monitoring the effect of pollutants on the environment are high on the governments list of priorities. The gas sensin g industry is eager to identify cheap and inherently simple sensing methodo logies with more sensitive sensing agents in order to meet new legislation for the detection of toxic gases at ever lower concentrations with greater selectivity, reversibility and reliability. One strategy is to utilise simp le colour changes in thin films of chromophores which occur as a result of exposure to low levels of such toxic gases. This paper describes the modifi cation, when exposed to chlorine gas, of the optical spectrum of a deposite d thin porphyrin Langmuir-Blodgett (LB) film coated onto a plastic substrat e. Films of this porphyrin (see structure of the symmetrically substituted meso-tetra(p-stearamidophenyl)porphyrin molecule) indeed exhibit a typical response time of <30 s Our spectroscopic measurements have been carried out , in situ, enabling dynamic gas response and recovery data to be presented. The data has been compared to that expected from simple adsorption kinetic s. The dependence of the gas response, on film thickness and deposition sur face pressure, have also been investigated. (C) 1999 Published by Elsevier Science S.A. All lights reserved.