Effect of Conformational Chirality on Optical Activity Observed in a Smectic of Achiral, Bent-Core Molecules

Abstract

Smectics of achiral, tilted bent-core liquid crystal molecules are chiral, but their optical activity is generally small. Here, we study the effect of conformational chirality on optical activity in smectic phases of an achiral, bent-core mesogen, W513. The neat material has a modulated B4 phase, which appears dark under crossed polarizers and shows no observable optical rotation under decrossed polarizers. However, mixtures of W513 with a rod-like mesogen, 8CB, show a conventional B4 phase, in which distinct left- and right-handed chiral domains with opposite optical activity are observed. The optical behavior of the mixtures is consistent with NMR results, which show a splitting of the carbonyl peak of the bent-core molecules into two, indicating a twisted conformation between the two molecular arms of the bent-core molecules as in conventional B materials.

Mirror symmetry breaking in liquids and liquid crystals

“…Therefore, optical rotation and CD do not give information about the helical coherence length, though there must be a uniform twist sense to observe optical activity. The helical twist of the chromophores in the helical conformers is also known to give high values of molecular optical rotation values, though intermolecular exciton coupling is usually the dominating effect [126].…”

Towards supramolecular nanostructured materials: control of the self-assembly of ionic bent-core amphiphiles

“…[21][22][23][24][25][26][27][28][29][30] A distinctive feature of this class of mesogen is the possibility of achieving not only polar organization but also spontaneous macroscopic chirality from achiral molecules, [31] e.g., the SmCP, the B7 mesophase or the very attractive B4-like phases, which are also named HNF-type (HNFs, HµFs and HLNCs) phases due to the formation of helical nanofilaments, [31][32][33][34][35][36][37][38][39][40] chiral mesophases with great promise and strong optical activity. [41][42][43][44][45] The mechanisms for the formation of all of these phases have not been fully explained, although different proposals have been published. [23,24,32,33,37,[41][42][43][46][47][48][49] Furthermore, potential applications have been claimed for diverse functional purposes and this has provided inspiration for nanoengineers working on chiral separation, nonlinear optics and photovoltaics.…”

“…[23,24,32,33,37,[41][42][43][46][47][48][49] Furthermore, potential applications have been claimed for diverse functional purposes and this has provided inspiration for nanoengineers working on chiral separation, nonlinear optics and photovoltaics. [41][42][43][44][45]47,50,51] Thus, BCLCs and their selfassembly have led to high expectations in supramolecular chemistry, materials science and nanotechnology. Moreover, the ability of bent-shaped mesogens to promote supramolecular aggregates, including chiral objects, by selfassembly in a solvent has also been reported.…”

Orientation Control of Helical Nanofilament Phase and Its Chiroptical Applications

“…In a subsequent study, we suggested a chiral sensing application with helical nanofilament-based photonic crystal (HNF-PC) (Figure 16) [20]. Similar to CLC and BP, HNF-PC also reflects CPL due to the chiral nanostructure [99][100][101][102][103][104][105][106]. As mentioned in Section 3.2, HNF is a racemic mixture, so r-and l-CPL are reflected in the right-and left-handed chiral domain, respectively.…”