Discotic liquid crystals of transition metal complexes 37: a thermotropic cubic mesophase having Pn3m symmetry exhibited by phthalocyanine-based derivatives

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 ( CnOPhO)(8)PcCu (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 [(CnO)(3)PhO](8)PcCu (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)(2)PhO](8)PcCu (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)(8)PcCu complexes (1) exhibited only one hexagonal columnar (Col(h)) mesophase and did not exhibit a cubic mesophase. Sixteen- chain- substituted [(CnO)(2)PhO](8)PcCu complexes (2) exhibited various columnar mesophases. In addition, the [(CnO)(2)PhO](8)PcCu (2) derivatives with n=12 and 14 exhibited a cubic mesophase with Pn3(-)m symmetry [Cub( Pn3(-)m)] over a very narrow temperature region (ca. 5-8 degrees C) at high temperatures. In contrast, the twenty-four-chain-substituted [(CnO)(3)PhO] 8PcCu (3) exhibited the Cub(Pn3(-)m) phase over a much wider temperature region (ca. 90 degrees 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 [(CnO)(2)PhO](8)PcCu (2, n=12, 14) and [(CnO)(3)PhO](8)PcCu ( 3, n=10, 12, 14) are the first discotic compounds exhibiting a thermotropic Cub(Pn3(-)m) phase.