Development and optimization of porphyrin gas sensing LB films

A series of meso-substituted metal-free porphyrins has been developed which show high sensitivity to NO2 gas in the sub-5 ppm concentration range. By selecting different substituents, it has been possible to improve in a systematic manner the response time and sensitivity of the porphyrin LB film to NO2. Initially, a sulphonamino substituent yielded a fairly long response time of around 450 s but this was shortened considerably when this substituent was changed for a stearamido group. Further modifications resulted in achieving a porphyrin LB film which exhibited a t50 response time of only 11 s. By using an optically inert calixarene host material in which the porphyrin guest was incorporated, it was possible to obtain t50 values as low as 5 s.