Metallophthalocyanines - Gas sensors, resistors and field effect transistors

The conventional metallophthalocyanines (PcM, M=Cu, Zn, Ni ...) are insulat ors when undoped. However, they possess accessible pi and pi* orbitals whic h make at least partial oxidization or reduction of the macrocycle possible with gases such as NO2 or O-3. This yields more or less conductive molecul ar materials. Their resistance is, therefore, a measurement of the concentr ation of the oxidizing or reducing species present in the surrounding atmos phere (resistors). In the case of rare earth bisphthalocyanines (in particu lar the lutetium derivative), the intrinsic density of charge carriers is n o longer negligible and the corresponding thin films or crystals are semico nductors. Gases such as NO2, at moderate concentrations and temperatures, c an afford completely oxidized materials: the doping process which increases the conductivity is therefore followed by an increase in the resistance. The same type of studies have been carried out using metallophthalocyanine as the electroactive (semiconductive) part of a field effect transistor (FE T). After a schematic description of the chemical phenomena arising in mole cular FET, a detailed chronology of their discovery is given. The influence of gases on FET characteristics is then reported. (C) 1998 Elsevier Scienc e S.A. All rights reserved.