Discotic liquid crystals of transition metal complexes 37*

*. For part 36, see Ichihara et al.1

: a thermotropic cubic mesophase having Pnm symmetry exhibited by phthalocyanine‐based derivatives

Abstract

In order to obtain discotic compounds exhibiting a cubic mesophase, we synthesised two new series of discotic compounds, 2,3,9,10,16,17,23,24‐octakis(4‐alkoxyphenoxy)phthalocyaninato copper(II) complexes, referred to as (C _n OPhO)₈PcCu (1, n = 10, 12, 14), and 2,3,9,10,16,17,23,24‐octakis(3,4,5‐trialkoxyphenoxy)phthalocyaninato copper(II) complexes, referred to as [(C _n O)₃PhO]₈PcCu (3, n = 10, 12, 14), which both contain octakis(phenoxy)phthalocyaninato copper(II) as the central core and eight or twenty‐four long alkoxy chains in the periphery, respectively. Their mesomorphic properties were compared alongside those of the previously reported 2,3,9,10,16,17,23,24‐octakis(3,4‐dialkoxyphenoxy)phthalocyaninato copper(II) complexes, referred to as [(C_nO)₂PhO]₈PcCu (2, n = 10, 12, 14). The phase transition behaviour of these discotic compounds (1–3) varies considerably with the number of peripheral chains. The eight‐chain‐substituted (C_nOPhO)₈PcCu complexes (1) exhibited only one hexagonal columnar (Col_h) mesophase and did not exhibit a cubic mesophase. Sixteen‐chain‐substituted [(C_nO)₂PhO]₈PcCu complexes (2) exhibited various columnar mesophases. In addition, the [(C _n O)₂PhO]₈PcCu (2) derivatives with n = 12 and 14 exhibited a cubic mesophase with Pn m symmetry [Cub(Pn m)] over a very narrow temperature region (ca. 5–8°C) at high temperatures. In contrast, the twenty‐four‐chain‐substituted [(C _n O)₃PhO]₈PcCu (3) exhibited the Cub(Pn m) phase over a much wider temperature region (ca. 90°C). Thus, it was revealed that these discotic compounds tend to exhibit a cubic mesophase on increasing the number and length of the peripheral chains. It should be emphasized that [(C _n O)₂PhO]₈PcCu (2, n = 12, 14) and [(C_nO)₃PhO]₈PcCu (3, n = 10, 12, 14) are the first discotic compounds exhibiting a thermotropic Cub(Pn m) phase.

*. For part 36, see Ichihara et al. 1

Acknowledgements

This work was supported by a Grant–in–Aid for the 21st Century COE Programme and a Grant–in–Aid for Science Research (18039013) in a Priority Area “Super–Hierarchical Structures” from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Notes

*. For part 36, see Ichihara et al. 1