Directing the Handedness of Helical Nanofilaments Confined in Nanochannels Using Axially Chiral Binaphthyl Dopants

Abstract

In this work, we demonstrate control of the handedness of semicrystalline modulated helical nanofilaments (HNF mod s) formed by achiral bent-core liquid crystal molecules by axially chiral binaphthyl-based additives as guest molecules solely under spatial nanoconfinement in anodic aluminum oxide nanochannels. The molecules of the same chiral additives are expelled from the HNF mod s in the bulk, and as a result thereof do not affect the handedness or helical pitch of bulk HNF mod s, resulting in an HNF mod conglomerate with chiralitypreserving growth within each domain. However, under confinement these axially chiral guest molecules, likely embedded in the HNF mod host, do affect the helicity of the HNF mod s. The configuration of the axially chiral molecules decides the HNF mod helix handedness and their concentration, and the helix angle is related to the helical pitch of the HNF mod s. In addition to local imaging data obtained by scanning electron microscopy, global studies by thin-film circular dichroism spectropolarimetry support the imaging results.

Directing Polymorphism in the Helical Nanofilament Phase

“…An HNF is formed by twisted smectic layers composed of BLC molecules (Figure 1). [15, 26, 27] Here, a dimeric molecule having aromatic groups on both sides of a central alkyl linkage with an odd number of C atoms (Figure 1 a) was used as BLC [19, 28, 29] . In particular, it was reported that D–n dimers with photoresponsive azobenzene moieties in their arm parts could be uniaxially oriented when irradiated with unpolarized UV light due to the Weigert effect [19] .…”

Orientation Control of Helical Nanofilament Phase and Its Chiroptical Applications

“…HNFs confined in the AAO nanochannel also show either left-or right-handed helical structures. To make the homochiral HNFs, Shadpour et al recently reported on controlling the handedness of HNF in the AAO channel using chiral dopants [70]. For this, the chiral dopant was mixed with bent-core LC molecules at 20 wt % or less and then injected into the AAO film (Figure 7a-c).…”

“…The rotated degree and its CD results are expressed together. Reprinted with permission from [70], Copyright 2020, American Chemical Society.…”

Control of the Induced Handedness of Helical Nanofilaments Employing Cholesteric Liquid Crystal Fields

“…The unique LC phases related to BC molecules are different from conventional LC phases observed in rod-like molecules [ 10 ]. Among the unique LC phases, the B4 phase is a semi-crystalline phase with hexatic LC ordering [ 12 ], in which achiral BC molecules spontaneously form chiral superstructures, i.e., helical nanofilaments (HNFs) [ 13 , 14 , 15 , 16 ]. Therefore, the B4 phase is also called the HNF phase.…”