Emerging Chiral Materials

Chirality has been one of the core research topics in the multidisciplinary fields of materials science, chemistry, biology, medicine, and physics. The subject of chirality in nanomaterials represents one of the most dynamic areas, and it has recently emerged as a new "growth point" of nanoscience. Of particular interest, recent advances in chiral materials endow the asymmetry-breaking capability to synthesize chiral materials with tunable and reconfigurable chiroptical properties, as well as various functions and emerging applications. Breakthroughs and technological developments have led to the study of many interesting properties of chiral nanocrystals, and some have demonstrated realistic potential, and may address key challenges at the heart of physical sciences. It is timely and necessary to organize a special issue to comprehensively review the state-of-the-art development of chiral materials and future research topics. To address recent advances in this rapidly growing field, we present this special issue of Advanced Materials on the topic of "Emerging Chiral Materials", which focuses on current developments, milestones achieved, and future research topics regarding chiral materials, including the following: synthesis of functional chiral materials, assemblies and reconfigurable chirality, origin of symmetry breaking, theory calculations of chirality, and applications of chiral materials. Leading experts have contributed to this issue, which covers the following five key aspects of emerging chiral materials: Major efforts should be made to prepare chiral nanostructures with high chiral purity from polymers, semiconductors, metals, and other materials. These individual nano-objects and superstructures are able to reveal unique chiroptical and other secondary chiral properties, as well as useful functions. Prof. Myongsoo Lee and Prof. Yongju Kim highlight the recent advances regarding the design principles and the construction of chiral supramolecular 2D materials, along with their chiroptical functions (article number 1905669). Prof. Katsuhiko Ariga and co-workers summarize the fabrication of chirality-featured architectonics from supramolecular materials, general molecular building blocks, chiral metal–organic frameworks, and chiral liquid crystals (article number 1905657). Based on the development of chiral nanocrystals construction, recent studies have focused on chiral inducement and controllable fabrication with high enantiomeric yield. Prof. Gil Markovich and co-workers discuss research on ligand-directing handedness, chiral amplification in enantiopure nanocrystal synthesis with emphasis on spontaneous symmetry breaking, the formation of chiral shapes, and chiroptical properties (article number 1905594). Furthermore, Prof. Ki Tae Nam and co-workers outline the fundamental principles of nanoscale chirality evolution with a focus on chiral morphologies correlated to or directed by chiral surfaces (article number 1905758). In addition, Prof. Nicholas A. Kotov and co-workers summarize the development of chiral nanoceramics and discuss their perspectives and challenges (article number 1906738). The assembly of achiral or racemic polymers or nanocrystals into high-order structures with specific handedness is another important direction in synthesis, which is particularly fruitful for chiral assemblies predicted a priori by design. Prof. Dario Pasini and co-workers present recent advances in molecular and supramolecular structures for aggregation-induced circularly polarized luminescence with a focus on emission amplification (article number 1908021). Prof. Yunbao Jiang and co-workers summarize the progress in chiral supramolecular aggregates with emphasis on the dependence of properties on nonlinear circular dichroism (article number 1905667). Prof. Quan Li and co-workers review the latest state and significant progress of emerging chiral liquid-crystalline nanostructured materials and their applications, as well as future opportunities and challenges in functional soft materials (article number 1801335). Prof. Quan Li and co-workers also summarize progress in the construction of photoprogramable mesogenic soft helical architectures with emphasis on the manipulation of chiro-optics (article number 1905318). Prof. Mark J. MacLachlan and co-workers outline the origin of chirality, the control of photonic properties, and the development of new composite materials of cellulose nanocrystal films (article number 1905876). Prof. Luis M Liz-Marzán and co-workers introduce the field of chiral liquid crystals formed from achiral molecules, and their correlation with resonant X-ray scattering properties (article number 1905591). In addition, new progress on nanocrystal assemblies and tunability enables further manipulation of chiroptical response and new applications. Prof. Nathaniel L. Rosi and co-workers highlight the key methodologies and major achievements in the development of helical nanomaterials with discussion on their specific merits and potential disadvantages. Some emerging applications, the future development, and the research focus are discussed and proposed (article number 1905975). Prof. Chuanlai Xu and co-workers review the recent progress in DNA-based assembly of plasmonic heterogeneous nanostructures with emphasis on structural engineering and optical responses tunability (article number 1907880). The reconfigurable biological tools and various nanocomponents provide the opportunity to switch the chiral configurations between d- and l-enantiomers as well as multi-band chiroptical properties. In the field of reconfigurable chirality, Prof. Na Liu and co-workers discuss different reconfiguration strategies, with a focus on geometries for controlling structural chirality as well as optical chirality (article number 1905640). The origin of chiral materials brings new insights for understanding homochirality on Earth. The chiral preference in nanoscale synthesis and assembly-related fabrication technologies help to provide insights into the phenomenon of spontaneous breaking of chiral equivalence in Nature. On this topic, Prof. Rongchao Jin and co-workers highlight metal–ligand surface bonding-induced chirality for nanoclusters. The different bonding modes of metal–ligands lead to different surface structures on nanoclusters, and give rise to various characteristic features of chirality (article number 1905488). Prof. Tingchao He and co-workers discuss research on synthesis of chiral transition metal oxides with emphasis on chiral origins with perspectives and future challenges discussed (article number 1905585). Prof. Dangyuan Lei and co-workers provide a brief review of recent achievements in chirality transfer from sub-nanometer biochemical molecules to sub-micrometer plasmonic metastructures with emphasis on physiochemical mechanisms and biosensing opportunities (article number 1907151). The importance of computational tools in the interpretation of spectroscopic data and identification of the chiral geometries at different scales is difficult to overestimate. The calculation theory of chirality has been greatly improved over the past few years and has been integrated with experimental advances in the field. On this topic, Prof. Zhiyong Tang and co-workers review the emerging progress on the theoretical background of magnetic circular dichroism in nanomaterials, providing an understanding of the band structure and degeneracy information of electronic transitions as well as the electronic states. The mechanism of geometry–magnetic circular dichroism activity enables elucidation and modulation of excitonic and plasmonic resonances (article number 1801491). Additionally, Prof. Alexander O. Govorov and Prof. Zhiming Wang summarize progress in the field of plasmonic chirality, with a focus on the theoretical study and the experimental advances of various nanochirality systems including molecular-plasmonic assemblies, chiral plasmonic nanostructures, chiral assembled nanostructures, and chiral metal metasurfaces and metamaterials (article number 1801790). It is the right time to assess practical applications of chiral nanostructures in different areas of technology. The nanoscale chirality of artificial chiral nanostructures offers many new application opportunities. Prof. Mark C. Hersam and co-workers review the current progress in chiral single-walled carbon-nanotubes-based computing devices, highlight the chirality enrichment and electronic functionality, and provide a perspective on next-generation single-walled carbon-nanotubes-based computing (article number 1905654). Prof. Minghua Liu and Prof. Pengfei Duan outline the recent status and progress of circularly polarized luminescence-active materials and highlight the findings for amplifying the luminescence dissymmetry factor, with emphasis on their application in multidisciplinary fields (article number 1900110). Chiral inorganic materials also offer a new potent platform for bioanalysis featuring ultrasensitive detection of DNA segments of different lengths, cancer antigens, small chiral molecules, and most recently micro-ribonucleic-acids. Prof. Hua Kuang and co-workers demonstrate the progress achieved during the past decade in chirality-associated biosensing, biolabeling, and bioimaging using individual chiral nanostructures or chiral assemblies, which includes discussions on the general design principles and performance of various chirality-based biosensors (article number 1802075). Recent studies have demonstrated that artificial chiral architectures and multi-level hierarchical chirality control for spectral tuning of polarization rotation in inorganic nanostructures will enable the development of emerging chiral materials. The future advances of chiral materials may be summarized from different aspects in this field: 1) The ability to fabricate or assemble complex chiral structures with much more control in enantiomeric purity is in great demand, which is an intrinsic challenge for all nanoarchitectures without exception. By varying nanoparticle anisotropy from subtle to high, the produced inorganic architectures with multicomponents in precise geometries and connecting patterns have distinct similarities with their biological counterparts. 2) Chiral materials produced by supramolecular chemistry, inorganic synthesis, self-assembly methods, lithography techniques, and other scalable manufacturing methods (e.g. glancing-angle vacuum, evaporation, etc.) will enable simple and scalable realization of homochiral fabrication with higher degrees of structural complexity. The complexity of chiral materials has markedly increased from nanoscale chain and nacre-like multilayers, to left- and right-handed helices and spiky hedgehog particles. 3) Theoretical methodology and experimental techniques are more likely to uncover the origins of chirality, and this is urgent for predicting potential routes in the fabrication of chiral structure and geometry evolutions. More importantly, how is the chirality of individual nanoparticles at ångström- and nanoscale being transferred through the scales to meso-, micro-, and macroscopic inorganic structures? 4) Chirality-related optical and physicochemical properties will lead to extensive potential applications. There will be great opportunities for developments both in experiment and theory, such as how do we realize fast modulation of circular polarization for quantum computing and biomedical imaging? 5) The prospects of manipulating spins, electrons and photons with multi-degrees of freedom, and polarization-based photonics or optoelectronics, are very promising for developing new-generation devices, such as molecular machines or macroscopic devices for better therapeutics. The ongoing and future studies in the area of chiral materials will likely benefit from a different, perhaps more comprehensive current assessment of the theoretical, experimental, computational, and translational aspects of this field. Hua Kuang is a Professor in Jiangnan University. She obtained her bachelor's degree from Jiangnan University in 2003, her master's degree in 2006, and her Ph.D. degree in 2009 from China Agricultural University, Beijing. She then joined Jiangnan University and worked as a postdoctoral fellow at City University of Hong Kong between 2012 and 2013. She foucuses on chiral probes preparation and bioanalysis. Chuanlai Xu is the Director of International Lab of Biointerface & Biodetection, Jiangnan University. His research interests include: 1) self-assembly of chiral nanomaterials and optical properties discovery; and 2) fabrication of nanodevices and their application in biotechnology. He combines nanotechnology and biological recognition to promote the real application of novel biosensors. His work related to more than 500 monoclonal antibodies has realized commercialization. Zhiyong Tang is a professor (since 2006) at the National Center for Nanoscience and Technology, China. He obtained his Ph.D. degree from Changchun Institute of Applied Chemistry with Professor Erkang Wang in 1999. His research interests are focused on controllable assembly, optical property manipulation, and catalytic application of inorganic nanomaterials.