Halogen sensing using thin films of crosswise-substituted phthalocyanines

Organic compound phthalocyanines (Pcs) are able to act as chemically sensit ive films because of the various physical effects induced in them by intera ction with a large number of gases. Specifically, they are used as thin fil m semiconducting gas sensors for the detection of halogens such as chlorine (Cl-2) and nitrogendioxide (NO2) as well as organic vapors. In a systematic test of different materials, crosswise-substituted with two alkylsulfanyl and two amino groups phthalocyanine films were investigated as sensitive materials for the detection of halogens. The sensing propertie s of these films were investigated by measuring both de and ac conductivity changes as a function of the gas concentration (0.05-0.15 ppm) at differen t temperatures (5-75 degreesC). The electrical properties of the films were determined by means of de and ac conductivity measurements under vacuum an d without vacuum. The results show that the conductivity curve goes through a maximum at a ce rtain temperature, T-max, depending on the molecular structure of the phtha locyanine films. The gas sensing measurements show that the sensors are hig hly sensitive to very low concentration of Br-2 and Cl-2 gases. The sensor signals are nearly reversible and reproducible even at room temperature. Th e crosswise substituted phthalocyanine thin films have good selectivity. (C ) 2001 Elsevier Science B.V. All rights reserved.