OPTICAL-RESPONSE OF MONOLAYER FILMS OF A METAL-FREE SULFONAMIDO-PORPHYRIN

The influence of gaseous chlorine on monolayers of metal-free meso-tet ra(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 sim ilar to 455 nm and similar to 660 nm appear, The rate of response has been measured as a function of deposition surface pressure and gas con centration. Repeated dosing experiments have shown that reversible and reproducible sensing action occurs provided that a threshold concentr ation is not exceeded. The recovery of the original optical spectrum c an be accelerated with moderate heat treatment (60 degrees C for 10 mi n). Ageing experiments have shown that the basic response of the monol ayer is not effected over a time period of at least 5 months. (C) 1998 Elsevier Science S.A. All rights reserved.