Modulating helical nanostructures in liquid crystal phase by molecular design

January 18, 2021


A team of researchers led by Assistant Professor Yuki Arakawa (Toyohashi University of Technology, Japan) has successfully developed sulfur-containing liquid crystal (LC) dimer molecules1) with oppositely directed ester bonds, which exhibit a helical liquid crystal phase, viz. twist-bend nematic (NTB) phase, 2) over a wide temperature range, including room temperature. Collaboration with a team at the Advanced Light Source research facility (Lawrence Berkeley National Laboratory, USA) revealed that the ester bond direction in the molecular structures largely impacts the pitch lengths of helical nanostructures in the NTB phase. It is expected that this molecular design can be used to tune the resultant physical properties of LC materials that would contribute to new LC technologies, such as LC laser, photo-alignment, and display technologies.


The NTB is a newly identified fluidic LC phase, which possesses a helical nanostructure with a pitch ranging from several to tens of nanometers, becoming a hot topic in the LC science community. Recently, various approaches were explored to apply the NTB materials to wavelength-tunable LC laser and photo-alignment technologies. In terms of practicality, LC materials must be devised by forming LC phases over a broad temperature range and at room temperature. However, molecules that exhibit the NTB phase over a wide temperature range, including room temperature, remain exceptionally rare. This has impeded deep evaluations of various properties and the development of new applications.

Assistant Professor Yuki Arakawa and his team in the Toyohashi University of Technology have been taking interest in developing novel sulfur-containing LC materials, especially for high-birefringence materials and twist-bend nematic LCs, based on thioether (R-S-R) linkages that contain sulfur, which is a component of hot springs and one of the few surplus resources in Japan. Sulfur or thioether bonds have high polarizability and are expected to be useful functional moieties for improving physical properties, such as refractive index and birefringence, compared with other bonds based on conventional atoms, such as methylene (carbon) and ether (oxygen).

Previously, Assistant Professor Yuki Arakawa and his team had successfully developed thioether-based bent molecules that exhibit the NTB phase. In this study, we attempted to devise new LC dimers by introducing oppositely directed ester bonds (i.e., -C=OO- and -O=CO-) to the thioether-based bent dimeric molecules and elucidate the influence of the ester bond direction on the NTB phase behaviors. The team succeeded in developing new molecules that exhibit NTB phases over a wide temperature range, including room temperature.

Furthermore, the team observed a phenomenon, in which the helical pitches (6-9 nm) of the molecules with O=CO ester were approximately double (11-24 nm) of those with C=OO ester (Figure 1). This is because the C=OO-ester dimers have more bent molecular geometries than the O=CO-ester dimers, resulting in enhanced molecular precession in the helical structure for the former than for the latter. Finely tuning the molecular design (i.e., the ester bond direction) enables the manipulation of helical nanostructures, which is particularly important for optical applications.

According to Assistant Professor Arakawa, "LC molecules that exhibit the helical NTB phase over a broad temperature range, including room temperature, remain rare. No studies have clearly revealed the structure-property relationship between molecular design and the resultant helical structure, i.e. how the helical nano-structures can be controlled by molecular design. We believe that our studies provide insight into it."
This paper was selected in Materials Advances HOT Article Collection, 2020.

Funding Agency:

This work was partly supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI grant numbers 17K14493 and 20K15351, the Naito Research Grant, and research grants from the Toukai Foundation for Technology and Toyohashi University of Technology.


Yuki Arakawa, Kenta Komatsu, Jun Feng, Chenhui Zhu, Hideto Tsuji. "Distinct twist-bend nematic phase behaviors associated with the ester-linkage direction of thioether-linked liquid crystal dimers." Materials Advances, 2020.
DOI: 10.1039/D0MA00746C

Technical terms:

1) A structure type of LC molecules in which two rigid structures are connected with a flexible alkyl chain spacer.

2) A helical liquid crystal phase in which bent molecules heliconically assemble to make a helical nano-structure.

Toyohashi University of Technology (TUT)

Related Molecules Articles from Brightsurf:

Finally, a way to see molecules 'wobble'
Researchers at the University of Rochester and the Fresnel Institute in France have found a way to visualize those molecules in even greater detail, showing their position and orientation in 3D, and even how they wobble and oscillate.

Water molecules are gold for nanocatalysis
Nanocatalysts made of gold nanoparticles dispersed on metal oxides are very promising for the industrial, selective oxidation of compounds, including alcohols, into valuable chemicals.

Water molecules dance in three
An international team of scientists has been able to shed new light on the properties of water at the molecular level.

How molecules self-assemble into superstructures
Most technical functional units are built bit by bit according to a well-designed construction plan.

Breaking down stubborn molecules
Seawater is more than just saltwater. The ocean is a veritable soup of chemicals.

Shaping the rings of molecules
Canadian chemists discover a natural process to control the shape of 'macrocycles,' molecules of large rings of atoms, for use in pharmaceuticals and electronics.

The mysterious movement of water molecules
Water is all around us and essential for life. Nevertheless, research into its behaviour at the atomic level -- above all how it interacts with surfaces -- is thin on the ground.

Spectroscopy: A fine sense for molecules
Scientists at the Laboratory for Attosecond Physics have developed a unique laser technology for the analysis of the molecular composition of biological samples.

Looking at the good vibes of molecules
Label-free dynamic detection of biomolecules is a major challenge in live-cell microscopy.

Colliding molecules and antiparticles
A study by Marcos Barp and Felipe Arretche from Brazil published in EPJ D shows a model of the interaction between positrons and simple molecules that is in good agreement with experimental results.

Read More: Molecules News and Molecules Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to