Liquid crystal-based chiral nanomaterials, a comprehensive review

Chirality is ubiquitous in living organisms and nature. Chiral architectures can be found at a variety of hierarchical levels, ranging from atomic and molecular to supramolecular, macroscopic, and galactic scales. However, chirality at the molecular level is inherently weak, and extending molecular chirality to nanomaterials could open up many new opportunities for the design and synthesis of emerging chiral functional nanomaterials with remarkable enhancement of chiroptical properties.

Chiral nanomaterials can be realized through the directed self-assembly of nanoscale achiral functional building blocks using various chiral soft templates such as DNA, peptide and protein, liquid crystal (LC), chiral polymer, and organogelators. Among the various chiral soft templates, liquid crystalline soft templates are very attractive because of their inherent long-range ordered molecular arrangements that couple liquid fluidity with crystal ordering from molecular to macroscopic hierarchical levels.

Recently, many researchers have devoted themselves to the design and synthesis of advanced chiral functional nanomaterials using liquid-crystalline soft templates. By exploiting the chiral self-assembly of different chiral liquid crystalline phases, it is possible to transfer their chirality and periodicity to functional nanomaterials with unique and unprecedented functionalities.

In an invited review article published in Light: Science & ApplicationsProfessor Ling Wang and Wei Feng from the School of Materials Science and Engineering, Tianjin University, China, Professor Quan Li from the Institute of Advanced Materials and School of Chemistry and Chemical Engineering, Southeast University, China, and their collaborators presented a comprehensive overview on the latest advances in chiral liquid crystal templating nanomaterials and their promising applications.

First, the key chiroptical properties of chiral nanomaterials are introduced. Then, an overview of chiral functional nanomaterials is presented, which includes chiral plasmonic nanomaterials based on thermotropic and lyotropic liquid crystal templates, as well as chiral luminescent nanomaterials based on various nanoscale building blocks such as emerging inorganic quantum dots, perovskite nanocrystals, and upconversion nanoparticles.

Finally, this Review concludes with an outlook on the new applications, challenges, and future possibilities of such fascinating chiral nanomaterials. This Review can not only deepen our understanding of the fundamentals of soft matter chirality, but also shed light on the development of advanced chiral functional nanomaterials for their diverse applications in optics, biology, catalysis, electronics, and beyond.

“Compared to emerging DNA-based soft templates, chiral liquid-crystalline templates are faster, cheaper, and more adaptable to direct the self-assembly of nanoscale building blocks into random and higher-order chiral nanomaterials over a wider range of scales, thanks to their inherent long-range ordered molecular assemblies, that combine the liquid fluidity with the crystal order from the atomic-molecular to the macroscopic level,” said Ling Wang and Quan Li.

“Various thermotropic and lyotropic liquid crystal templates have been applied to fabricate chiral plasmonic nanomaterials with enhanced circular dichroism (CD), enhanced dissymmetry factor, and dynamic chiroptical responses, which have many potential applications, such as e.g. B. negative refractive index, of paramount importance are materials, ultrasensitive biosensing, enantioselective analysis and more.”

“A variety of new nanoscale functional building blocks, such as inorganic quantum dots, perovskite nanocrystals, and upconversion nanoparticles, have been employed for the design and synthesis of novel chiral luminescent nanomaterials that exhibit significantly enhanced circularly polarized luminescence, which is important in many fields Emerging fields such as life sciences, 3D display, information encryption, chiral spintronics and enantioselective photochemistry could find applications.”

“Despite the great achievements, the development of chiral functional nanomaterials based on a bottom-up soft-template strategy is still in its early stages and there are still many challenges that need to be addressed to enable breakthrough research in this important field to motivate. The first is the development of chiral functional nanomaterials with high optical asymmetry g-factors (g_Section for absorption and g_lumen for luminescence), since the values ​​given are still far from the theoretical value of ±2.”

“The second is to endow the chiral functional nanomaterials with tunable chiroptical activity for different target wavelengths ranging from the ultraviolet, visible, near-infrared to terahertz ranges. Importantly, future research should pay more attention to bridging the research gap from lab-scale proof-of-concept to large-scale synthesis of chiral functional nanomaterials and their integration into hierarchical multi-material architectures and even more complex advanced ones functional devices,” they added.

“The unique combination of liquid crystalline nanoscience with nanoscale chirality and emerging bottom-up self-assembly will bring vitality to the development of programmable and reconfigurable chiral functional nanomaterials with unlimited possibilities. Future efforts by scientists and engineers with multidisciplinary research backgrounds are sure to bring new turns into fundamental breakthrough and technological applications of the emerging soft matter chirality and truly advanced chiral functional nanomaterials, affecting biology, optics, electronics, spintronics, physics, chemistry, materials science, device engineering, and other interdisciplinary areas,” they said.