Stabilization of Nondiscoid Columnar Liquid Crystals:  Studies of Unsymmetrical Copper Bis-β-diketonates

Abstract

A series of copper(bis-β-diketonate) complexes are reported which display columnar liquid-crystal phases with a hexagonal disordered structure (D hd). The complexes do not have the disc-shape characteristic of most D hd materials, but produce a disc shape by forming dimers with 90o rotations between nearest neighbors. In the liquid-crystalline state this dimerized nature produces short-range rotational correlations. Three side-chain copper bis-β-diketonates with a single phenyl substituent, 2, are not liquid crystalline, and it was found that an extension of the mesogenic core is necessary to introduce liquid crystallinity. The simple phenyl analogues, 3a, are monotropic, and the addition of electron-withdrawing substituents to the phenyl moiety, 3b − d, results in a stabilization of the mesophase. These substituents produce favorable dipolar interactions which stabilize the mesophase. Consistent with this explanation, electron-donating substituents are not effective at stabilizing the mesophase. Substitution of the complex with thiophene groups rather than phenyls, 4, produces stable mesophases with greatly lowered melting and clearing points. This latter result indicates that thiophene substitution provides dispersive forces which destabilize the crystal phase. Thiophene substitution may provide a general method for reducing transition temperatures in metallomesogens.

Convergent Synthesis of Columnar Twins and Tetramers from Triphenylene Building Blocks – The First Example of a Columnar Spiro-Twin

“…This alignment is conceivable both for a rectangular and a hexagonal lattice. The analogous formation of "correlated columnar" mesophases was observed by Swager for non-symmetrical copper bis(β-diketonate) complexes [27] . Despite the absence of optical textures in the case of tetramers 7, X-ray diffraction experiments of an unoriented sample of 7f clearly indicated the presence of a columnar mesophase.…”

Functional star-shaped tris(triazolyl)triazines: columnar liquid crystal, fluorescent, solvatofluorochromic and electrochemical properties

“…3). This pattern, together with texture observed by POM, led us to propose that the low-angle halo corresponds to the (1 0) reflection of a hexagonal columnar mesophase, [53][54][55] giving cell parameters of 43.2 A for TB6 and 41.6 A for TB9. The absence of other reflections at low diffraction angles apart from the (1 0) reflection is common in diffraction patterns of hexagonal columnar mesophases 41,53-56 and it is due to a minimum in the form factor, which precludes the observation of peaks in this region.…”

Discotic Liquid Crystals: From Tailor‐Made Synthesis to Plastic Electronics

“…Swager and co‐workers investigated in detail the chemistry of copper bis‐β‐diketonate complexes. Surprisingly, even the unsymmetrical systems such as 108 display stable enantiotropic hexagonal columnar mesophases (Scheme ) 206. Substituent effects of various unsymmetrical copper and palladium β‐diketonate complexes 108 were systematically studied by Lai and co‐workers 207.…”