Discotic liquid crystals of transition metal complexes 37* : a thermotropic cubic mesophase having Pn m 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 [(CnO)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 (CnOPhO)8PcCu complexes (1) exhibited only one hexagonal columnar (Colh) mesophase and did not exhibit a cubic mesophase. Sixteen‐chain‐substituted [(CnO)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 [(CnO)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