Synthesis and characterization of new mesomorphic octakis(alkylthio)-substituted lead phthalocyanines and their films

The syntheses of new octakis (alkylthio)-substituted phthalocyanines of Pb(II) (1a and 2a) are described. These compounds are very soluble in most common organic solvents. They have been fully characterized using elemental analysis, NMR, infrared and UV-Vis spectroscopy. The mesogenic properties of these new materials were studied by differential scanning calorimetry and optical microscopy. These phthalocyanine derivatives are liquid at room temperature and form columnar-hexagonal (Col(h)) mesophases below -10 degrees C. It has been indicated that the addition of methylene bridges to the phthalocyanine (Pc) core increases the clearing point temperatures. Also, the coordination of Pb2+ with the phthalocyanine core decreases the clearing point temperatures and the liquid crystal phase transition temperatures. Thin films of octakis(alkylthio)-substituted Pb(II) phthalocyanines la and 2a were prepared by the method of spin-coating. To obtain films with an ordered structure the film of la was slowly cooled from room temperature down to -10 degrees C. Sandwich structures of the form Au/PbPc(1a)/Au were prepared for the investigation of their electrical properties. It was shown that a slowly cooled Au/ PbPc(1a)/Au structure demonstrates repeatable and stable electrical switching behaviour for applied bias voltages between -1 V and +1 V. (C) 2007 Elsevier Ltd. All rights reserved.