Discotic liquid crystals of transition metal complexes 56+: Synthesis of mesogenic phthalocyanine-fullerene dyads and influence of the substitution position of alkoxy chains and the kind of terminal groups on appearance of the helical supramolecular structure

We have synthesized twelve novel discotic columnar liquid crystals based on a phenoxy-group-substituted phthalocyaninato copper(II) complex having the same alkoxy chain of C16H33O at different positions in the phenoxy group: the parent compounds {0a similar to 0c-16} and the OH-substituted compounds {3a similar to 3c-16}, the OFBA-substituted compounds {2a similar to 2c-16} and the C-60-substituted dyads {1a similar to 1c-16}. The letters of a, b and c mean substitution positions of C16H33O group at m-, p-and m, p-, respectively. We have investigated the influence of both substitution position of the alkoxy chains and the kind of terminal groups (OH, OFBA and C-60) on the mesomorphism and the helical supramolecular structure, by using DSC, POM and temperature-variable small angle X-ray diffraction measurements. As a result, an additional big peak (Peak H) tends to appear at around 2 theta = 1.1 degrees in the X-ray diffraction patterns only for the dyads {1a similar to 1c-16} but not for the other compounds, {0a similar to 0c-16}, {3a similar to 3c-16} and {2a similar to 2c-16}, regardless of the substitution positions of the alkoxy group. Moreover, we revealed that both the m-substituted derivative 1a-16 and the m, p-substituted derivative 1c-16 gave Peak H, but that only the p-substituted derivative 1b-16 did not give Peak H among these three dyads {1a similar to 1c-16}. From the temperature-variable small angle X-ray diffraction measurements for the m, p-substituted derivative 1c-16 using two different sample preparation methods, we proved that the Peak H originates from a helical pitch of fullerenes. We also pointed out that the m-substituted long alkoxy chains are at least needed to form the helical supramolecular structure in the present (PhO)(6)PcM-C-60-based dyads.