Investigation of the photoconductive properties of thiophene substituted metallo-phthalocyanines†
The synthesis of 4-(thiophen-3-ylethynyl)phthalonitrile was achieved via the Sonogashira cross-coupling reaction. Herein, we report the synthesis of symmetrical metallo-phthalocyanines with cobalt, zinc, and manganese as the metal ions, and tetrakis(ethynylthiophene) groups substituted at the peripheral positions. The new compounds have been characterized by using mass, 1H NMR, 13C NMR, FT-IR and UV-vis spectroscopy. Dark and photoconductivity measurements were carried out on spin coated thiophene substituted metallo-phthalocyanines at various temperatures fixed between 300 and 440 K. Photocurrent generation and charge transport mechanisms are discussed as well. The evaluation of the photoconductive properties of these compounds indicated that the photocurrent generation efficiency and charge transport mechanism exhibited a strong temperature dependence. On the other hand, conductivity measurements revealed that the temperature dependence of the conductivity can be described by the Arrhenius type exponential equation under dark conditions. Furthermore, it was found that the photoconductive behavior of the film can be described successfully by the variable range hopping model for the whole investigated temperature range.