Discotic liquid crystals of transition metal complexes 29: mesomorphism and charge transport properties of alkylthio-substituted phthalocyanine rare-earth metal sandwich complexes

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Abstract
A series of bis[octakis(alkylthio)phthalocyaninato]rare-earth-metal(III) discotic compounds, [(CnS)8Pc]2M (M = Eu(III), Tb(III), Lu(III); n = 8, 10, 12, 14, 16, 18), has been synthesized. The mesomorphic and supramolecular structures have been investigated by using differential scanning calorimetry, polarization microscopy and temperature-dependent X-ray diffraction techniques. From the X-ray diffraction and spectroscopic results, it was revealed that in each of the rare-earth compound classes, [(CnS)8Pc]2Eu (n = 10, 12), [(CnS)8Pc]2Tb (n = 10, 12, 14) and [(CnS)8Pc]2Lu (n = 10, 12), derivatives were found which displayed a novel unique pseudo-hexagonal mesophase. The temperature dependence of the one-dimensional intracolumnar charge carrier mobilities, Σμ1D, has been measured for [(C12S)8Pc]2Lu and [(C18S)8Pc]2Lu using the PR-TRMC (pulse-radiolysis time-resolved microwave conductivity) technique. The mobility values in both the K and D phases are more than an order of magnitude larger than found previously for [(C12O)8Pc]2Lu and are close to the maximum values ever found for discotic materials. The lack of a decrease in Σμ1D at the mesophase to isotropic liquid transition suggests that these compounds may represent the first liquid phase organic semiconducting materials.

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