Optical detection of chlorine gas using LB films of a zinc porphyrin dimer

We report on the optical response of the zinc porphyrin dimer 1 to gaseous chlorine. In situ optical measurements have been made on organized thin films of 1 during exposure to a stream of chlorine gas at low concentrations (0.5–10 ppm). Typical response time at 2 ppm for the dimer monolayer is 35 s for 50% loss in monitored absorbance. Response-controlling factors such as LB deposition conditions, substrate type, target gas concentration, film ageing and heat treatment have been investigated with a view to developing a prototype chlorine-sensing device to be used for personal safety purposes. Rate constants for the response processes have been deduced.