Inverse Helical Nanofilament Networks Serving as a Chiral Nanotemplate

Abstract

Herein, an epoch-making method based on bottom-up templating is proposed for the fabrication of a chiral nanoporous film that provides a chiral environment in which to confine nematic liquid crystals. A helical nanofilamental network of bent-core molecules was utilized as a three-dimensional mold, and thus the fabricated chiral nanoporous film has an inverse nanohelical structure. The presence of a chiral superstructure was confirmed by the observation of circular dichroism signals. Upon refilling this chiral nanoporous film with an achiral nematic liquid crystal, distinct circular dichroism signals appeared due to the transfer of chirality from the inverse helical nanofilaments to the achiral nematic liquid crystal. The circular dichroism signals can be readily modulated by external stimuli, such as the application of heat or an electric field. In addition, by refilling the chiral nanoporous film with a nematic liquid crystal doped with fluorescent dye, it exhibits stimuli-responsive circularly polarized luminescence. The proposed approach has huge potential for practical applications, such as for chiroptical modulators and switches and biological sensors.

Orientation Control of Helical Nanofilament Phase and Its Chiroptical Applications

“…Finally, the circularly polarized luminescence was generated from the achiral fluorescence dye. The chirality of HNF can be transferred not only to small molecules but also to polymeric networks [90]. This chiral polymer can be used as a template that can induce chirality in additional small molecules.…”

“…In Stage 3, the CD was amplified in a broad wavelength range, and it was proven that the chirality was not only transferred but also amplified, with the confined nematic LC medium inside the chiral polymer. The chirality of HNF can be transferred not only to small molecules but also to polymeric networks [90]. This chiral polymer can be used as a template that can induce chirality in additional small molecules.…”

“…(c) CD spectra for each stage with opposite chiral domains.The inset graph shows enlarged image of the spectrum in the wavelength range of 300 to 350 nm in Stage 2. Reprinted with permission from[90], Copyright 2020, American Chemical Society.…”

Enhancement of Luminescence Dissymmetry Factor in Nano-Segregated Phase Generated by Phase Separation between Helical Nanofilaments and Liquid-Crystalline Smectic A Phase

“…The CPL spectra were calculated from the wavelength dependence of the AC and DC components and the phase of the modulated signal. The details are provided in References [4,10,15]. The g lum value was evaluated using the following correlation:…”

“…A mixed system, consisting of an achiral bent-core (BC) molecule and rod-like nematogen, has been reported as a promising chiroptic material [4][5][6][7][8]. In this system, nano-sized phase separation-between helical nanofilaments (HNF) originating from the BC molecule and the calamitic liquid-crystalline (LC) nematic (N) phase originating from rod-like nematogen-shows high chiropticity, such as optical rotatory power or circular dichroism [5,9,10].…”