Spectroscopic properties and conductivity of thin films of partially reduced metallo-phthalocyanines

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Abstract
Thin films of reduced phthalocyanine have been prepared by co‐condensation, under high vacuum, of cobalt or iron phthalocyanine (Pc) with potassium. The absorption spectra of the reduced Pc have been determined and found to be strongly dependent upon the reduction state of the film, especially in the visible region. Four reduction states corresponding to the mono‐, di‐, tri‐, and tetraanion of CoPc were observed and assignment of the electronic structure was made on the basis of similarity with the spectra of phthalocyanine in solution. The conductivity of each film was measured as a function of its state of reduction. The film conductivity was found to be isotropic. Large increases of conductivity from 10−10 to 1–2 Ω−1 cm−1 occurred by steps which correlated well with the state of reduction of the Pc. The temperature dependence of the conductivity was determined between 80 and 330 K. Based on the transport results, a Mott–Davis type model with hopping between localized states is proposed for the conduction mechanism.