Discotic Liquid Crystals of Transition Metal Complexes, 5: Double Melting Behavior and Double Clearing Behavior of Discogens

Abstract

Two new octa-substituted disk-like bis(β-diketonato) copper(II) complexes, 8C₈-Cu and 8C₈O-Cu, have been synthesized. The same type of octa-substituted copper complexes, SC₉O-Cu, which was synthesized for the first time by A. M. Giroud-Godquin et al., has also been prepared. The thermal behavior of these three complexes was investigated by means of microscopic observations and DSC measurements. It was found that the 8C₈-Cu exhibits not a discotic mesomorphism but a usual double melting behavior via the isotropic liquid, and that the 8C₈O-Cu exhibits an unusual double melting behavior via the discophase which had not been reported by A. M. Giroud-Godquin et al. Furthermore, it was found that the 8C₈O-Cu exhibits a new thermal phenomenon of “double clearing behavior” which is originated from a superheating of the transition from the crystalline phase to the discotic phase. Such double clearing behavior of the 8C₈O-Cu is the first example in the mesomorphic compounds, so far as we know.

Key Words:

• discotic liquid crystal
• transition metal complex
• Bis(β-diketone) copper (II)
• double melting behavior
• double clearing behavior