Abstract
Cobalt(II), nickel(II), copper(II) and zinc(II) phthalocyanines substituted by eight alkoxy chains in the peripheral (2,3,9,10,16,17,23,24) positions were prepared. The alkoxy chain lengths are octyloxy (C8H17O), dodecyloxy (C12H25O) and hexadecyloxy (C16H33O). Studies by polarized optical microscopy and high-temperature X-ray diffraction revealed that all the complexes are liquid-crystalline and that they exhibit a hexagonal columnar mesophase (Colh). Transition enthalpies were determined by differential scanning calorimetry (DSC). The clearing point could only be observed for the compounds with the hexadecyloxy chains. The melting points depend on the central metal ion: Ni II < Cu II ≈ Co II < Zn II . The clearing point could only be observed for the compounds with the hexadecyloxy chains, and it was found that the nature of the metal ion has negligible influence on the clearing point.
Highlights
The ability of phthalocyanines to form liquid-crystalline phases was first demonstrated by Piechocki et al for the peripherally octakis(dodecyloxymethyl) substituted copper(II) phthalocyanine.[1]
For the metallophthalocyanines with eight peripheral alkoxymethyl chains, the melting point increases in the order PbII < MnII < CuII
We report on the influence of the central metal ion (M = CoII, NiII, CuII, ZnII) on the transition temperatures of metallophthalocyanines with eight peripheral alkoxy chains (Figure 1)
Summary
The ability of phthalocyanines to form liquid-crystalline phases was first demonstrated by Piechocki et al for the peripherally octakis(dodecyloxymethyl) substituted copper(II) phthalocyanine.[1] This compound exhibits a disordered hexagonal columnar mesophase over a wide temperature range (from 53 °C to more than 300 °C). Since this pioneering work many different liquid-crystalline phthalocyanines have been prepared with the aim to explore the influence of parameters such as the number of side chains, the length of the side chains, branching of the chains and the type of linking group (alkoxy, alkyl, alkoxymethyl, ...). According to these authors, the mesophase range of the nickel(II) compound is about 100 °C less than that of the corresponding cobalt(II) compound
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