Discotic liquid crystals of transition metal complexes 52: Synthesis and homeotropic alignment of liquid crystalline phthalocyanine-fullerene dyad bridged by vanillin

Abstract

We have synthesized a novel liquid crystalline phthalocyanine(Pc)-fullerene(C[Formula: see text] dyad (C[Formula: see text]S)[Formula: see text]PcCu-VAN-C[Formula: see text] (3a) bridged by an inexpensive natural product of vanillin (VAN), instead of the previous long [Formula: see text]-alkylene chain spacer. We have also synthesized a comparative dyad (C[Formula: see text]S)[Formula: see text]PcCu-OPh-C[Formula: see text] (3b) bridged by [Formula: see text]-hydroxybenzaldehyde (OPh), in order to investigate the influence of the methoxy group in the vanillin moiety on homeotropic alignment between two glass plates. Very interestingly, homeotropic alignment could be observed only for the dyad (C[Formula: see text]S)[Formula: see text]PcCu-VAN-C[Formula: see text] (3a) having a methoxy group in the vanillin moiety, whereas it could not be observed for the dyad (C[Formula: see text]S)[Formula: see text]PcCu-OPh-C[Formula: see text] (3b) having no methoxy group at the phenoxy group. It is very noteworthy that such a slight difference in these molecular structures between 3a and 3b becomes a crucial point to show the homeotropic alignment. Each of the dyads, 3a and 3b, showed two hexagonal ordered columnar (Col[Formula: see text] mesophases. Each of the Col[Formula: see text] mesophases in 3a and 3b gave an additional very strong reflection peak named as Peak H in a very low angle region of the SAXS (small angle X-ray scattering) pattern. Peak H could be established, from two different SAXS measurement methods, as one pitch in a helical structure of the fullerenes around the Pc column.