Formation of Columnar and Cubic Mesophases by Calamitic Molecules:  Novel Amphotropic Biphenyl Derivatives

Abstract

Novel amphiphilic 4,4′-disubstituted biphenyl derivatives incorporating a hydrophilic 5,6-dihydroxy-3oxahexyloxy group and a lipophilic chain have been synthesized by Pd-catalyzed cross-coupling reactions of phenyl boronic acids with 4-(5,6-dihydroxy-3-oxahexyloxy)bromobenzenes. The thermotropic and lyotropic mesomorphic behavior of these compounds were investigated by polarizing microscopy, by differential scanning calorimetry, and by means of X-ray diffraction. Thereby the influence of the length of the alkyl chain, the type of connecting unit between alkyl-chain and the rigid core (O vs CH 2 ), and the influence of lateral substituents and of the molecular chirality on the mesomorphic properties were investigated. All compounds have smectic A-phases as the high-temperature mesophases. Additionally, columnar phases were found for the long chain 4′-alkoxy-4-(5,6-dihydroxy-3-oxahexyloxy)biphenyls 2c-f without lateral substituent and for the 4-(5,6-dihydroxy-3-oxahexyloxy)-4′-dodecyloxy-3′-methylbiphenyl 10. All other laterally substituted biphenyl derivatives 9 and 11-15 and the 4′-alkyl substituted compound 8 display only smectic phases. The influence of protic solvents (formamide and ethylene glycol) on the liquid crystalline properties was studied. The columnar mesophases and S C -phases are destabilized by addition of protic solvents whereas the S Aphases are stabilized. Furthermore, binary mixtures of the amphiphilic biphenyl derivatives with each other have been investigated. Complete miscibility was found for the S A -phases and the columnar phases of the compounds 2c-f. However the columnar phases of the nonsubstituted compounds 2c-f and the 3′-methyl substituted derivative 10 do not have an uninterrupted miscibility. Cubic phases (Pn3m or Pn3) and additional columnar phases were induced in the contact regions. Thus, the same diversity of different kinds of mesophases as in lyotropic systems and in the thermotropic phase sequence of polycatenar compounds is found. It is proposed that the cubic and columnar mesophases of these rodlike molecules result from the collapse of the smectic layer structures into ribbons.

Cubic and Other3DThermotropic Liquid Crystal Phases and Quasicrystals

“…While this cubic phase is common in lyotropic systems, only a handful of reports of thermotropic phases with Pn3m symmetry have appeared [50,[68][69][70][71], and it is questionable whether any of these is genuine, or at least, whether any represents the double diamond structure. In most cases, the quality and/or angular range of published diffraction data, invariably powder diffractograms, are insufficient to make a judgment, and in some cases, the distribution of intensities among Bragg peaks is very far from that expected from a double diamond network structure.…”

Mesomorphic Hydrogen‐Bonded Complexes of Complementary Semiperfluorinated Components

“…Thermotropic bicontinuous cubic phases composed of ribbons so far have been discussed for amphiphilic rod-like biphenyl derivatives. [20] The 1/1 associates presented here can be regarded as hydrogen-bonded semiperfluorinated polycatenar mesogens that contain shorter but more polar rigid cores compared with covalently linked benzoate analogues. Interestingly, rectangular columnar phases with C2mm plane group have never been reported for covalent polycatenar liquid crystals.…”

Formation of a Double Diamond Cubic Phase by Thermotropic Liquid Crystalline Self‐Assembly of Bundled Bolaamphiphiles

“…It has been reported recently that in both the Im3 m and the Ia3 d phase,t he direction of the rods twists along the network segment and that the match between helix pitch and rodlength determines the observed phase type. [13] Although there have been sporadic accounts of other suspected Cub bi phases, [14][15][16][17][18] there has been no confirmed report of at hird Cub bi phase in thermotropic LCs to date. [19] Herein we report what, to our knowledge,i st he first confirmed case of at hermotropic Cub bi phase with the "double diamond" (DD) structure.T he structure,f ound in abolamphiphile with abranched side-chain, was determined by X-ray diffraction (XRD).…”