Novel Chiral Effect That Produces the Anisotropy in 3D Structured Soft Material: Chirality-Driven Cubic−Tetragonal Liquid Crystal Phase Transition

Abstract

The effect of chirality on the liquid crystal organization has been systematically investigated between (S,S)- and (R,R)-isomers of a dichiral azobenzene compound. The racemic mixture was found to show the cubic phase (Im3m), indicating that the studied compound shows the cubic structure without the effect of chirality. However, with increasing optical purity of the racemic mixture, the cubic (Im3m) structure changes into the tetragonal phases (I422 and I4(1)22), which have been known as the SmQ phases, via a chiral cubic phase (I432). This is the first example of "chirality-driven" cubic-tetragonal structural change observed in liquid crystal systems, which is experimental evidence showing the novel type of chiral effect that produces the anisotropy in the structures of soft materials. The emergence of the anisotropy, i.e., the cubic-tetragonal phase transformation, is also induced by means of photoinduced phase transition of the SmQ phases based on cis-trans photoisomerization of the azobenzene compounds.

Cubic and Other3DThermotropic Liquid Crystal Phases and Quasicrystals

“…Tetragonal distortion of the Ia3d phase (a = 76.7Å) to an I4 1 /acd symmetry (a = 73.2Å, c = 80.9Å) has in fact been observed for the racemic mixture mentioned earlier, adding support to the existence of a connection between bicontinuous cubic and SmQ structures [8]. It has also been claimed that in a chiral calamitic compound, with increasing chiral component, phase transitions are observed from Im3m symmetry in the racemic mixture to a chiral cubic I432 structure, then to the I422 SmQ structure [155]. However, some doubt remains as to whether the X-ray diffraction patterns truly support the assignment of the Im3m and I432 phases.…”

“…Model (b) can be ruled out on the basis of quantitative examination of the X-ray diffraction pattern. (After Refs[154,155]. )…”

The Solution of the Puzzle of Smectic‐Q: The Phase Structure and the Origin of Spontaneous Chirality

“…[15] Another commonly observed phase in such compounds is the triplenetwork cubic phase, [16] which has recently been found to be chiral and can form in both chiral and achiral compounds,in the latter through dynamic mirror symmetry breaking. [18] In the current work we report the observation of the chiral SmQ phase in achiral rod-like compounds and present anew structural model showing SmQ to be an on-cubic bicontin-uous phase formed by interwoven orthogonal helices,the first of its kind. It has also been reported that by increasing enantiomeric excess,starting from what appears to be an achiral triple-network cubic phase in ar acemate, ap hase transition to SmQ is observed.…”

“…It has also been reported that by increasing enantiomeric excess,starting from what appears to be an achiral triple-network cubic phase in ar acemate, ap hase transition to SmQ is observed. [18] In the current work we report the observation of the chiral SmQ phase in achiral rod-like compounds and present anew structural model showing SmQ to be an on-cubic bicontin-uous phase formed by interwoven orthogonal helices,the first of its kind.…”

An electrically-stabilized liquid-crystalline phase: origin and application

“…3 Recently, a new dichiral azobenzene ((S,S)-AZO-PB, Fig. 3 Recently, a new dichiral azobenzene ((S,S)-AZO-PB, Fig.…”