Synthesis and Supramolecular Chemistry of Novel Liquid Crystalline Crown Ether-Substituted Phthalocyanines: Toward Molecular Wires and Molecular Ionoelectronics

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Abstract

The synthesis of the metal-free and the dihydroxysilicon derivatives of tetrakis[4’,5’-bis(decoxy)benzo-18-crown-6]phthalocyanine is described. The metal-free phthalocyanine is liquid crystalline and exhibits a crystalline phase to mesophase transition at 148 °C. The structures of the crystalline phase and the mesophase are determined by X-ray measurements. The metal-free compound strongly aggregates in chloroform solution to form a gel. Electron micrographs show that this gel contains a network of fibers, each of which is built up of parallel strands of supermolecules having the thickness of one molecule and a length of several micrometers. The strands are formed by a process of self-assembly involving up to 10e4 molecules. They can be considered as being molecular cables, containing a central electron wire, four ion channels, and a surrounding insulating hydrocarbon mantle. The silicon derivative contains two axial hydroxy groups which prevent the molecule from aggregating. This compound is not liquid crystalline. It forms a stable monolayer at the air-water interface. In this layer, the phthalocyanine planes are oriented parallel to the water surface. The monolayers can be transferred onto glass substrates by a Y-type deposition. The resulting Langmuir-Blodgett film is built up of bilayers containing slipped face-to-face phthalocyanine dimers. The monolayer is capable of binding alkali metal ions from the subphase, as is concluded from surface area-surface pressure isotherms. The binding constant for potassium ions has been determined by analyzing the isotherms as a function of the concentration of this metal ion. The dihydroxysilicon phthalocyanine can be polymerized to form a polysiloxane.

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