Discotic liquid crystals of transition metal complexes 39: columnar mesomorphism and homeotropic alignment speed of sandwich-type of double-deckers and triple-deckers based on phthalocyaninato lutetium metal complexes

Abstract

A series of sandwich-type metal complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-dialkoxyphenoxy)phthalocyaninato]lutetium(III) ({[( C n O )2 PhO ]8 Pc }2 Lu (n = 8−16): double-deckers (2)), were synthesized. As the by-product, tris[2,3,9,10,16,17,23,24-octakis(3,4-diakoxyphenoxy)phthalocyaninato]dilutetium(III) ({[( C n O )2 PhO ]8 Pc }3 Lu 2 (n = 8, 9, 11, 12, 14, 16): triple-deckers (3)) were successfully separated. The mesomorphic properties of these double-deckers (2) and triple-deckers (3) were investigated using a polarization microscope, differential scanning calorimetry and temperature-dependent X-ray diffraction techniques. The double-deckers (2) showed Colh , Cub and Coltet mesophases for n ≥ 10. On the other hand, the triple-deckers (3) showed only a Colr mesophase for n = 8, only a Coltet mesophase for n = 14, and both Colr and Coltet mesophases for n = 9, 11, 12 and 16. For the Coltet mesophase, both the double-deckers (2) and the triple-deckers (3) exhibited spontaneous homeotropic alignment in a large area. In comparison with the homeotropic alignment of these present lutetium complexes 2, 3 and the previous copper complexes, 2,3,9,10,16,17,23,24-octakis(3,4-dialkoxyphenoxy)phthalocyaninato copper(II) ([( C n O )2 PhO ]8 PcCu (n = 9-14): single-decker (1)), the alignment was fast, slow and fast, respectively, in the order of the single-deckers (1), double-deckers (2) and triple-deckers (3). Very interestingly, the complexes 1 and 3 which have flat Pc macrocycles gave fast alignment, whereas the complexes, 2, which have non-flat Pc macrocycles, gave slow alignment. Thus, it was revealed for the first time that the flatness of discotic liquid crystalline molecules influences the speed of homeotropic alignment.