Unique Chiroptical Properties Research Articles

Organic Circularly Polarized Room-Temperature Phosphorescence: Strategies, Applications and Challenges.

Organic circularly polarized luminescence (CPL) plays crucial roles in chemistry and biology for the potential in chiral recognition, asymmetric catalysis, 3D displays, and biological probes. The long-lived luminescence, large Stokes shift, and unique chiroptical properties make organic circularly polarized room-temperature phosphorescence (CPP) a new research hotspot in recent years. Nevertheless, achieving high-performance organic CPP is still challenging due to the sensitivity and complexity of integrating triplet excitons and polarization within organic materials. This review summarizes the latest advances in organic CPP, ranging from design strategies and photophysical properties to underlying luminescence mechanisms and potential applications. Specifically, the design strategies for generating CPP are systemically categorized and discussed according to the interactions between chiral units and chromophores. The applications of organic CPP in organic light-emitting diodes, sensing, chiral recognition, afterglow displays, and information encryption are also illustrated. In addition, we present the current challenges and perspectives on developing organic CPP. We expect this review to provide some instructive design principles to fabricate high-performance organic CPP materials, offering an in-depth understanding of the luminescence mechanism and paving the way toward diverse practical applications.

Organic Circularly Polarized Room‐Temperature Phosphorescence: Strategies, Applications and Challenges

Organic circularly polarized luminescence (CPL) plays crucial roles in chemistry and biology for the potential in chiral recognition, asymmetric catalysis, 3D displays, and biological probes. The long‐lived luminescence, large Stokes shift, and unique chiroptical properties make organic circularly polarized room‐temperature phosphorescence (CPP) a new research hotspot in recent years. Nevertheless, achieving high‐performance organic CPP is still challenging due to the sensitivity and complexity of integrating triplet excitons and polarization within organic materials. This review summarizes the latest advances in organic CPP, ranging from design strategies and photophysical properties to underlying luminescence mechanisms and potential applications. Specifically, the design strategies for generating CPP are systemically categorized and discussed according to the interactions between chiral units and chromophores. The applications of organic CPP in organic light‐emitting diodes, sensing, chiral recognition, afterglow displays, and information encryption are also illustrated. In addition, we present the current challenges and perspectives on developing organic CPP. We expect this review to provide some instructive design principles to fabricate high‐performance organic CPP materials, offering an in‐depth understanding of the luminescence mechanism and paving the way toward diverse practical applications.

Helical Polyallenes: From Controlled Synthesis to Distinct Properties.

Polyallenes with appropriate pendants can form stable helices and exhibit significant optical activity. These helical polyallenes contain reactive double bonds that allow for further functionalization, making them a class of chiral functional materials with broad application prospects. This review article delves into the intricacies of synthesizing well-defined helical polyallenes through controlled synthetic methodologies, including helix-sense selective living polymerization, regioselective and asymmetric living polymerization, and one-pot block copolymerization of allenes with aryl monomers. The systemically outlined characteristics of the resulting helical polyallenes and related copolymers are summarized include their unique chiroptical properties, stimuli-responsiveness, helix-induced chiral self-assembly, and circularly polarized luminescence (CPL). Additionally, current challenges and future perspectives in the research of controlled synthesis, functionalities, and applications of helical polyallenes are discussed in detail.

Synthesis of Anisotropic Gold Microparticles via L‐Glutathione‐Mediated Pathways in Droplet Microfluidics

AbstractMicrofluidic‐assisted synthesis of nanoparticles has generated significant interest for its precise control and high throughput capabilities. Among various nanomaterials, gold nanoparticles (AuNPs) have shown remarkable potential in numerous applications, such as disease detection, photothermotherapy, drug delivery, and even defense applications. Recent synthesis strategy of peptide‐mediated method has sparked greater interest by offering unique chiroptical properties and their applications in biomedical applications. In this study, the use of droplet microfluidics is explored for the synthesis of peptide‐mediated AuNPs, aiming to accelerate automated production via flow chemistry. This method leads to the formation of anisotropic gold particles, with sizes ranging from hundreds of nanometers to the micron scale. The interfacial energy is identified at the water/oil interface as a critical factor influencing this outcome, with L‐glutathione (L‐GSH) playing a significant role in the development of hyper‐branched structures. These results demonstrate the capability of droplet microfluidics in producing anisotropic gold particles at micron scales, presenting new possibilities for the advancement of nanoparticle synthesis techniques.

Carborane-Cluster-Wrapped Copper Cluster with Cyclodextrin-like Cavities for Chiral Recognition.

Chiral atomically precise metal clusters, known for their remarkable chiroptical properties, hold great potential for applications in chirality recognition. However, advancements in this field have been constrained by the limited exploration of host-guest chemistry, involving metal clusters. This study reports the synthesis of a chiral Cu16(C2B10H10S2)8 (denoted as Cu16@CB8, where C2B10H12S2H2 = 9,12-(HS)2-1,2-closo-carborane) cluster by an achiral carboranylthiolate ligand. The chiral R-/S-Cu16@CB8 cluster features chiral cavities reminiscent of cyclodextrins, which are surrounded by carborane clusters, yet they crystallize in a racemate. These cyclodextrin-like cavities demonstrated the specific recognition of amino acids, as indicated by the responsive output of circular dichroism and circularly polarized luminescence signals of Cu16 moieties of the Cu16@CB8 cluster. Notably, a quantitative chiroptical analysis of amino acids in a short time and a concomitant deracemization of Cu16@CB8 were achieved. Density functional tight-binding molecular dynamics simulation and noncovalent interaction analysis further unraveled the great importance of the cavities and binding sites for chiral recognition. Dipeptide, tripeptide, and polypeptide containing the corresponding amino acids (Cys, Arg, or His residues) display the same chiral recognition, showing the generality of this approach. The functional synergy of dual clusters, comprising carborane and metal clusters, is for the first time demonstrated in the Cu16@CB8 cluster, resulting in the valuable quantification of the enantiomeric excess (ee) value of amino acids. This work opens a new avenue for chirality sensors based on chiral metal clusters with unique chiroptical properties and inspires the development of carborane clusters in host-guest chemistry.

Circularly Polarized Luminescent π‐Conjugated Chiral Nanorings and Nanobelts

AbstractMolecular chirality plays a pivotal role across the disciplines of chemical and physical sciences, as well as holding significant implications in the realms of medicine and technology. Chiral macrocycles have attracted recent interests in synthetic chemistry, material science, and supramolecular chemistry. Due to the cyclic arrangements of stereogenic elements or special orientations confined in the rigid structures, π‐conjugated chiral macrocycles are expected to be highly luminescent, and configurationally stable, and thus serve to develop high‐performance chiroptical materials. Given the rapid progress achieved in this new area in recent years, it is significant to highlight new concepts and breakthroughs. This minireview will offer the overview of a wide range of π‐conjugated chiral macrocycles from traditional molecules which include the axially, helically, and planar chiral skeletons to the new chiral nanobelts with a focus on the structure‐function relationship between chiral molecules and the unique chiroptical properties.

Induced Huge Optical Activity in Nanoplatelet Superlattice.

Chiral superstructures with unique chiroptical properties that are not inherent in the individual units are essential in applications such as 3D displays, spintronic devices, biomedical sensors, and beyond. Generally, chiral superstructures are obtained by tedious procedures exploring various physical and chemical forces to break spatial symmetry during the self-assembly of discrete nanoparticles. In contrast, we herein present a simple and efficient approach to chiral superstructures by intercalating small chiral molecules into preformed achiral superstructures. As a model system, the chiral CdSe nanoplatelet (NPL) superlattice exhibits a giant and tunable optical activity with the highest g-factor reaching 3.09 × 10-2 to the excitonic transition of the NPL superlattice, nearly 2 orders of magnitude higher than that of the corresponding separated chiral NPLs. The theoretical analysis reveals that the chiral deformation in the NPL superlattice induced by the chiral perturbation of the small chiral molecules is critical to the observed huge optical activity. We anticipate that this research lays a foundation for understanding and applying chiral inorganic nanosystems.

Axially-chiral boramidine for detailed (chir)optical studies.

The inclusion of boron atoms into chiral π-conjugated systems is an effective strategy to unlock unique chiroptical properties. Herein, the preparation and characterization of a configurationally stable axially-chiral boramidine are reported, showcasing absorption in the UV domain, deep-blue fluorescence (Φ up to 94%), and ca. |10-3| gabs and glum values. Detailed photophysical studies and quantum-chemical calculations clearly elucidate the deactivation pathways of the emissive state to triplet excited states, involving increased spin-orbit coupling between the lowest singlet excited state and an upper triplet state.

Fabrication of Chiral Plasmonic Photocatalyst By Circularly Polarized Light and Enantioselective Hydrogen Generation Activity

Introducing chirality in nanostructures has been explored actively in various field, such as sensing, optoelectronics and catalysts, due to its unique chiroptical properties. Especially in photochemistry, considering the synergistic interaction between chiral plasmonics and polarized light, they can be utilized to improve efficiency and selectivity of catalytic reaction. In this work, we synthesized chiral plasmonic photocatalysts, (R)-,(L)- Au/C3N4, through photoreduction of gold precursor on C3N4 substrate under the irradiation of circularly polarized light (CPL) as a means to induce chirality. Then, we demonstrated that the efficiency of hydrogen generation can be increased by matching the chirality of the CPL with the photocatalyst, which was 2-fold enhanced than chiral mismatching conditions. This can be explained by the asymmetric hot carrier formation of chiral plasmonic structures under CPL excitation. Also, the reactivity of water molecule with photocatalyst surface was confirmed through in-situ FT-IR, showing the enhanced interaction under chiral matching conditions. This study could pave the way for advancing chiral light-matter interactions and explore the application of novel device, particularly toward chiral-induced photocatalytic performance.

Chiral [1]rotaxanes with a two-fold bridge based on phenylacetylene macrocycles (PAMs): two different chiroptical properties created by 7PAM

Abstract We describe the unique chiroptical properties of chiral [1]rotaxanes 1 and 2 based on the assembly of an achiral ring of phenylacetylene macrocycle (7PAM) and an achiral p-phenylene ethynylene rod with a two-fold bridge. In both cases, mechanical helical chirality is generated by the relative occupation of the ring and rod. Through the intramolecular transmission of the mechanical helical chirality to the bridge, we demonstrate that two different chiral conformations were present in a particular form of enantiomers in 2.

Helix-Induced Asymmetric Self-Assembly of π-Conjugated Block Copolymers: From Controlled Syntheses to Distinct Properties.

Conspectusπ-Conjugated polymers have gained significant interest because of their potential applications in optoelectronics, bioelectronics, and other domains. The controlled synthesis of π-conjugated block polymers optimizes their performance and enables novel properties and functions. However, precise control of the self-assembled architectures of π-conjugated polymers remains a formidable challenge. Inspired by the precise helical architectures of biomacromolecules, the helical polymers and the supramolecular helical assemblies have gained significant attention. Helical polymers with an excess of one-handed helicity can be optically active with a strong tendency toward self-assembly. Incorporating a helical polymer into a π-conjugated polymer can induce asymmetric helical assemblies, leading to novel chiral materials with unique functionalities.To control the self-assembly of architectures, π-conjugated polymers are usually synthesized into block copolymers by incorporating a polymer with self-assembling characteristics. Although various π-conjugated block copolymers have been produced, precise and asymmetric self-assembly is still challenging and has rarely been addressed. Incorporating helical polymers into the π-conjugated polymers can induce a precise and asymmetric self-assembly, which transfers the chirality of the helical polymer block to the π-conjugated polymer, resulting in chiral supramolecular architectures with unique chiroptical properties and functionalities. However, synthesizing hybrid block copolymers containing two distinct polymer blocks is complicated. Some general strategies such as connecting the chain ends of two preformed homopolymers and extending the chain of a prefabricated π-conjugated polymer with a second monomer are time-consuming and require complex synthetic protocols. Therefore, developing novel strategies for the facile synthesis of π-conjugated block copolymers with a predictable molar mass, low dispersity, and tunable composition is of practical importance.Recently, we investigated a controlled synthesis of helical polyisocyanides, helical polyallenes, and helical polycarbenes by developing advanced Pd(II) and Ni(II) catalysts. These helical polymers were successfully incorporated into π-conjugated polymers, including polythiophene, polyfluorene, and poly(phenyleneethynylene), via a one-pot sequential living block polymerization of the two distinct monomers using Pd(II)- or Ni(II)-complexes as catalysts. As a result, a variety of well-defined π-conjugated block copolymers containing helical polymeric blocks were readily synthesized. Although the copolymerized monomers possess different structures and polymerization mechanisms, the one-pot block copolymerization followed a living polymerization mechanism and provided the desired π-conjugated block copolymers in high yields with controlled molar mass, narrow size distribution, and tunable composition.Remarkably, the helical polymeric block induces the π-conjugated block copolymer asymmetric self-assembly into a supramolecular, one-handed helical architecture resulting in distinct optical properties. More interestingly, by utilizing the crystallization of conjugated blocks and one-handed helical blocks, the crystallization-driven and helix-induced precise asymmetric living self-assembly yielded a family of uniform and single-handed helical architectures with controlled dimensions, narrow distribution, and well-defined helicity. The transfer of helical chirality to the supramolecular architectures rendered the achiral π-conjugated blocks with unique chiroptical properties such as the emission of white light over a broad optical spectrum and the circularly polarized luminescence.

Inherently chiral calixarenes by a catalytic enantioselective desymmetrizing cross-dehydrogenative coupling.

Under the catalysis of PdBr2 and a chiral phosphoramidite ligand, the upper-rim mono (2-bromoaroyl)-substituted calix[4]arene derivatives underwent a facile enantioselective desymmetrization reaction to afford 9H-fluorene-embedded inherently chiral calixarenes in good yields with excellent enantioselectivities. The transannular dehydrogenative arene-arene coupling reaction proceeded most probably through an oxidative addition of the Caryl-Br bond to a ligated palladium catalyst followed by a sequence of an enantioselective 1,5-palladium migration and an intramolecular C-H arylation sequence. This new family of inherently chiral calixarenes possesses unique chiroptical properties thanks to their highly rigid structure induced by the 9H-fluorene segment.

Self-assembled inorganic chiral superstructures.

Controlled assembly of inorganic nanoparticles with different compositions, sizes and shapes into higher-order structures of collective functionalities is a central pursued objective in chemistry, physics, materials science and nanotechnology. The emerging chiral superstructures, which break spatial symmetries at the nanoscale, have attracted particular attention, owing to their unique chiroptical properties and potential applications in optics, catalysis, biology and so on. Various bottom-up strategies have been developed to build inorganic chiral superstructures based on the intrinsic configurational preference of the building blocks, external fields or chiral templates. Self-assembled inorganic chiral superstructures have demonstrated significant superior optical activity from the strong electric/magnetic coupling between the building blocks, as compared with the organic counterparts. In this Review, we discuss recent progress in preparing self-assembled inorganic chiral superstructures, with an emphasis on the driving forces that enable symmetry breaking during the assembly process. The chiroptical properties and applications are highlighted and a forward-looking trajectory of where research efforts should be focused isdiscussed.

Static Retention of Dynamic Chiral Arrangements for Achiral Shear Thinning Metal-Organic Colloids.

Chiral compounds are known to be important not only because they are the fundamental components of living organisms, but also for their unique chiroptical properties. In recent years, scientists have fabricated several chiral organic supramolecular aggregates by using chiral physical fields, such as vortex flow. Herein, the relationship between dynamic chiroptical properties and rheological nature is discussed, suggesting the shear thinning properties of non-Newtonian fluids might help colloidal particles adopt a chiral arrangement in vortices. Furthermore, the storage modulus of colloids could be increased by adding a linking agent, which successfully kept the dynamic chiroptical properties in the static state. Moreover, the salt effect on the host-guest interaction involved in the colloids was studied, the results suggested a significant enhancement of the transferred dynamic circular dichroism for the achiral guest molecule.

Solvent-Driven Chirality Switching of a Pillar[4]arene[1]quinone Having a Chiral Amine-Substituted Quinone Subunit.

Several new chiral pillar[4]arene[1]quinone derivatives were synthesized by reacting pillar[4]arene[1]quinone (EtP4Q1), containing four 1,4-diethoxybenzene units and one benzoquinone unit, with various chiral amines via Michael addition. Due to the direct introduction of chiral substituents on the rim of pillar[n]arene and the close location of the chiral center to the rim of EtP4Q1, the newly prepared compounds showed unique chiroptical properties without complicated chiral resolution processes, and unprecedented high anisotropy factor of up to −0.018 at the charge transfer absorption band was observed. Intriguingly, the benzene sidearm attached pillar[4]arene[1]quinone derivative 1a showed solvent- and complexation-driven chirality inversion. This work provides a promising potential for absolute asymmetric synthesis of pillararene-based derivatives.

Dual-Mode Chiral Self-Assembly of Cone-Shaped Subphthalocyanine Aromatics.

Columnar polymers and liquid crystals obtained from π-conjugated cone-shaped molecules are receiving increasing interest due to the possibility of obtaining unconventional polar organizations that show anisotropic charge transport and unique chiroptical properties. However, and in contrast to the more common planar discotics, the self-assembly of conic or pyramidic molecules in solution remains largely unexplored. Here, we show how a molecular geometry change, from flat to conic, can generate supramolecular landscapes where different self-assembled species, each of them being under thermodynamic equilibrium with the monomer, exist exclusively within distinct regimes. In particular, depending on the solvent nature-aromatic or aliphatic-cone-shaped C3-symmetric subphthalocyanine 1 can undergo self-assembly either as a tail-to-tail dimer, showing monomer-dimer sigmoidal transitions, or as a head-to-tail noncentrosymmetric columnar polymer, exhibiting a nucleation-elongation polymerization mechanism. Moreover, the experimental and theoretical comparison between racemic and enantiopure samples revealed that the two enantiomers (1M and 1P) tend to narcissistically self-sort in the dimer regime, each enantiomer showing a strong preference to associate with itself, but socially self-sort in the polymer regime, favoring an alternate stacking order along the columns.

Looking Ahead

On behalf of the Particle & Particle System Characterizations editorial team, I wish our readers a Happy New Year. It has been my greatest pleasure to lead the journal as the Editor-in-Chief since early 2018, with the invaluable support of the editors, and my colleagues, Floriano Cuccureddu (Berlin, Germany), Duoduo Liang (Beijing, China), and Ulf Scheffler (Weinheim, Germany). Over the past months, I have had the honor to read first-hand cutting-edge research on nanostructured materials for applications spanning biomedicine, energy, technology, and environmental protection. Table 1 provides a list of some of the most-read articles published in the journal in 2018. They give us a feeling for the journal topics that attracted the readers most. We are thankful to all our authors for entrusting their work to us. In 2018, Particle & Particle System Characterizations published two topical issues. Artificial Photosynthesis – Mimicking Nature for Renewable Energy Production (2018/01) highlighted important concepts in artificial photosynthesis for versatile energy- and environment-related applications. The issue was guest-edited by Wee-Jun Ong, Zhiqun Lin, and Kazunari Domen. Sara Skrabalak, Jingyi Chen, Svetlana Neretina, and Dong Qin assembled the issue Bimetallic Nanomaterials Bring New Properties and Functions (2018/05), showcasing recent advances in the synthesis, characterization, and properties of bimetallic nanoparticles. Both topical issues received a strong resonance from the scientific community, with many papers featuring among the most-read (Table 1) and most-cited (Web of Science) articles published in the journal over the past year. Progress in the field of nanoparticles and nanostructures is rapid, and they have been demonstrated to exhibit unique chiroptical properties. In the coming year, a new special issue guest-edited by Shaowei Chen, Zhiyong Tang, and Jianping Xie, will be dedicated to this research area. The time scientists dedicate to review the work of their peers is fundamental to the reviewing process and is invaluable to help us publish high quality science. We are therefore thankful to all our referees. In particular, I would like to thank the referees who have been most active in the past two years with the journal (Table 2). Particle & Particle System Characterizations is in continuous development. In response to the interests of the scientific community and new scientific trends, the journal's Advisory Board was renewed in early 2018. We are grateful to the board members who helped us in the past and are pleased to receive the support of Sara Bals (Univ. of Antwerp, Belgium), Shaowei Chen (Univ. of California, USA), Mircea Cotlet (Brookhaven National Laboratory, USA), Hong Jin Fan (Nanyang Technological Univ., Singapore), Steve Granick (Ulsan National Institute of Science and Technology, Korea), Kimberly Hamad-Schifferli (Univ. of Massachusetts Boston, USA), Seong-Ju Hwang (Ewha Womans Univ. Seoul, Korea), Rafal Klajn (Weizmann Institute of Science, Israel), Xing Yi Ling (Nanyang Technological Univ., Singapore), Juewen Liu (Univ. of Waterloo, Canada), Zhuang Liu (Soochow Univ., China), Jwa-Min Nam (Seoul National Univ., Korea), Thomas Nann (Victoria Univ. of Wellington, New Zealand), Julia Pérez-Prieto (Univ. of Valencia, Spain), Paresh C. Ray (Jackson State Univ., USA), Sara Skrabalak (Indiana Univ., USA), Tatsuya Tsukuda (Univ. of Tokyo, Japan), Jianfang Wang, (Chinese Univ. of Hong Kong, China), Claire Wilhelm (Paris Diterot Univ., France), Gi-Ra Yi (Sungkyunkwan Univ., Korea), Yan Yu (University of Science and Technology of China, China), Fan Zhang (Fudan Univ., China), Dejian Zhou (Univ. of Leeds, UK). We have already had the pleasure of collaborating with a few of the new board members, and we look forward to working with them all in the future. We all know, finding time to stay up-to-date with recent research literature is not easy. Starting in January 2019, Particle & Particle Systems Characterization offers a virtual issue: Best of Particle. This issue is a collection of some of the most interesting articles published in the journal. The articles are selected by the journal editors and are free to access for a limited time. We hope Best of Particle will be helpful to our readers to identify relevant recent papers in their research area. Best of Particle will be updated on a regular basis – so stay in touch and check for new content!

An Inherently Chiral Au24 Framework with Double‐Helical Hexagold Strands

Abstract2,3‐bis(diphenylphosphino)butane enantiomers (chiraphos, L) used as chiral auxiliaries results in the preferential formation of an unprecedented Au24 framework with inherent chirality. The crystal structure of [Au24L6Cl4]2+ (1) has a square antiprism‐like octagold core twinned by two helicene‐like hexagold motifs, where the inherent chirality is associated with the helical arrangement. The clusters carrying (R,R)‐ and (S,S)‐ diphosphines had right‐ and left‐handed strands, respectively. Circular dichroism spectra showed peaks in the visible to near‐IR region, some of which did not coincide with absorption bands, suggesting the enantiomeric Au24 frameworks possess unique chiroptical properties. The Au24 frameworks were thermally robust, which could be attributed to the superatomic concept (18 e− system) and the steric constraint effects of the bridging ligand units.

An Inherently Chiral Au24 Framework with Double-Helical Hexagold Strands.

2,3-bis(diphenylphosphino)butane enantiomers (chiraphos, L) used as chiral auxiliaries results in the preferential formation of an unprecedented Au24 framework with inherent chirality. The crystal structure of [Au24 L6 Cl4 ]2+ (1) has a square antiprism-like octagold core twinned by two helicene-like hexagold motifs, where the inherent chirality is associated with the helical arrangement. The clusters carrying (R,R)- and (S,S)- diphosphines had right- and left-handed strands, respectively. Circular dichroism spectra showed peaks in the visible to near-IR region, some of which did not coincide with absorption bands, suggesting the enantiomeric Au24 frameworks possess unique chiroptical properties. The Au24 frameworks were thermally robust, which could be attributed to the superatomic concept (18 e- system) and the steric constraint effects of the bridging ligand units.

Acyclic artificial nucleic acids with phosphodiester bonds exhibit unique functions

Artificial nucleic acids (XNAs) have potential as therapeutic agents and fluorescent probes. These acyclic nucleic acid mimics have several advantages, including facile chemical synthesis and resistance to nuclease-mediated cleavage. Here we review our recent progress on the preparation of acyclic XNAs. Acyclic D-threoninol nucleic acid (D-aTNA) forms an extremely stable homo-duplex with complementary D-aTNA, but D-aTNA does not form a stable duplex with either DNA or RNA. Serinol nucleic acid (SNA), which has nucleobases on a serinol backbone, forms stable hybrid helices with both DNA and RNA and has unique chiroptical properties. Both chirality and helicity of an SNA duplex depend on its sequence. L-aTNA, which is an enantiomer of D-aTNA, has the highest affinity for complementary DNA and RNA among these three XNAs. Attempts to apply these XNAs as drugs, fluorescent probes, and nanomaterials are underway. Although chemical differences among these XNAs are small, all have unique properties, and XNAs with different functional characteristics will be found by chemically modifying these XNAs. In this focus review, we overview our recent works on acyclic artificial nucleic acids (XNAs). Three acyclic XNAs, D-aTNA, SNA and L-aTNA have been developed. D-aTNA can form extremely stable homo-duplex, whereas it shows a high orthogonality with natural nucleic acids. SNA oligomers can change their helicity and chirality depending on sequences. L-aTNA can form stable duplexes with both DNA and RNA. Owing to unique properties of these XNAs, they should find application as tools in biology, biotechnology and nanotechnology.