A study of iodine influence on the electrical properties of phthalocyanines and polyphthalocyanines of some metals

Abstract

Phthalocyanines and their polymers have recently been the subject of many investigations. They are used widely for new gas sensors. They have excellent stability against heat, light, moisture and oxygen [1-3]. The interest in them results from the fact that they are organic systems whose doping with acceptor or donor increases their conductivity [4-6]. However, metal phthalocyanines (PcMe) and their polymers (pPcMe) and especially poly(iron phthalocyanine) [7-9] are good catalysts for oxygen reduction. The properties of poly(iron phthalocyanine) make this polymer suitable for use in fuel cells. The properties of metal phthalocyanines and poly(metal phthalocyanines) may be modified in two ways. First, as a result of doping with donors or acceptors, and, secondly, by annealing in different atmospheres [10]. Modification my be accompanied by a dramatic change in electrical conductivity and/or an increase in the catalytic (or electrocatalytic) activity [11]. For example, the heating of nickel phthalocyanine [10] to 750 K in a helium atmosphere leads to an increase in the conductivity by eight orders of magnitude. The increase in conductivity enhances the catalytic properties because it also increases the catalytic (electrocatalytic) activity [12]. The enhancement of conductivity is probably a result of a more-extented conjugated structure which promotes charge-carrier mobility in the annealed material compared with in the untreated polymer. The positive influence of heat treatment on the electroactivity of poly(iron phthalocyanine) was also observed earlier [13]. In the case of poly(iron phthalocyanine) annealing may lead to two effects: first, an increase in conductivity and, secondly, cross-linking of poly(iron phthalocyanine) with the participation of the surface support. This cross-linking facilitates transport of charges between the surface support and the active-phase pPcFe, and leads to an increase in electroactivity [13]. The aim of this work was to investigate the influence of iodine doping on the electrical and other physicochemical properties of some metal phthalocyanines and their polymers. The metal phthalocyanines were synthesized by heating mixtures of anhydrous metal salts with phthalonitrile in molten urea at 570 K for 2-3 h in air. In the poly(metal phthalocyanines) syntheses the phthalonitrile was replaced by pyromellitedianhydride. The pure products from these reactions were crystalline materials, as evidenced by