Optical response of monolayer films of a metal-free sulfonamido-porphyrin

Abstract

The influence of gaseous chlorine on monolayers of metal-free meso-tetra(4-amino sulfonyl)phenylporphyrin is discussed. These films exhibit characteristic intense optical absorption bands in the region 400–700 nm. Upon exposure to chlorine vapour in the concentration range 0.1–10 ppm, the Soret and Q-bands decrease in intensity and new bands at ∼455 nm and ∼660 nm appear. The rate of response has been measured as a function of deposition surface pressure and gas concentration. Repeated dosing experiments have shown that reversible and reproducible sensing action occurs provided that a threshold concentration is not exceeded. The recovery of the original optical spectrum can be accelerated with moderate heat treatment (60°C for 10 min). Ageing experiments have shown that the basic response of the monolayer is not effected over a time period of at least 5 months.