Discotic liquid crystals of transition metal complexes 42: the detailed phase structures and phase transition mechanisms of two Cub mesophases shown by discotic liquid crystals based on phthalocyanine metal complexes

摘要

We found in our previous works that the sandwich-type phthalocyanine-based rare earth metal complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-dialkoxyphenoxy)phthalocyaninato] lanthanoid(III) ({[(CnO)2PhO]8Pc}2M, M = Eu and Lu, n = 8–16) (1 and 3), exhibited two thermotropic cubic mesophases, Cub1 and Cub2, together with columnar mesophases. It is rare that the discotic liquid crystalline compounds show the cubic mesophase. We revealed that their symmetries of the lower temperature Cub1 mesophase and the higher temperature Cub2 mesophase were Pn3 – m and Pm3 – n, respectively. However, their detailed phase structures were not revealed in the previous works. In this work, we have synthesized a series of novel sandwich-type phthalocyanine-based terbium complexes, bis[2,3,9,10,16,17,23,24- octakis(3,4-dialkoxyphenoxy)phthalocyaninato]terbium(III) ({[(CnO)2PhO]8Pc}2Tb, n = 8–16) (2). Their mesomorphic properties have been investigated using polarization microscope, DSC and temperaturedependent X-ray diffraction techniques. As the result, the present Tb complexes (2) also showed two cubic mesophases, Cub1 (Pn3 – m) and Cub2 (Pm3–n), together with columnar mesophases, as well as the previous Eu homologs (1) and Lu homologs (3). We have furthermore investigated by using temperature-dependent electronic absorption spectroscopy to reveal their detailed phase tructures and phase transition mechanism of these two Cub mesophases. We have revealed that the Cub1 (Pn3 –m) mesophase forms a bicontinuous structure consisting of branched columns like jungle gym, ut that the Cub2 (Pm3 –n) mesophase forms a discontinuous structure consisting of short columns like drums that resulted from the cutting off of the branched columns.