Liquid Crystal Behaviour of 2,3,9,10,16,17,23,24-Octakis(octyloxy)phthalocyanine-containing Gadolinium Sandwich Complexes

Abstract

A series of six liquid crystalline phthalocyaninato gadolinium sandwich complexes that include two double-decker species Gd(Pc)[Pc(OC8H17)8] (1) [Pc(OC8H17)8 = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyanine] and Gd[Pc(OC8H17)8]2 (2) and four triple-decker species (Pc)Gd(Pc)Gd[Pc(OC8H17)8] (3), (Pc)Gd[Pc(OC8H17)8]Gd(Pc) (4), (Pc)Gd[Pc(OC8H17)8]Gd[Pc(OC8H17)8] (5), and Gd2[Pc(OC8H17)8]3 (6) have been designed and their liquid crystal phase transition behaviour has been systematically studied by differential scanning calorimetry, X-ray diffraction, and polarized optical microscopy. The clearing point seems to show a dependence on the molecular structure of the sandwich compounds, increasing from double-decker to triple-decker along with an increase in the number of substituted 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyanine ligand both in the double- and triple-decker compounds. The liquid crystalline mesophases display a hexaganol columnar and/or rectangular columnar molecular arrangement depending on the molecular structure of sandwiches, which suggests the cooperation of the π–π stacking and the influence of octyloxy side chains on the liquid crystal formation. In addition, the textures of this series of double- and triple-decker sandwich complexes formed in the liquid crystalline mesophase exhibit high stability even after the mesophases of the compounds are heated to a clear isotropic liquid and cooled to room temperature, which is expected to be an efficient method to construct molecular electronic devices.