Chirality Transfer Research Articles

Discovering New Type of Lead‐Free Cluster‐Based Hybrid Double Perovskite Derivatives with Chiral Optical Activities and Low X‐Ray Detection Limit

Abstract2D chiral hybrid perovskites have recently emerged as outstanding semiconductor materials. However, most of the reported 2D chiral perovskites have limited structural types and contain high levels of toxic lead, which severely hinders their further applications. Herein, by using a mixed‐cation strategy, an unprecedented type of lead‐free cluster‐based 2D chiral hybrid double perovskite derivatives are successfully obtained, [(R/S‐PPA)4(IPA)6Ag2Bi4I24]·2H2O (1‐R and 1‐S), and [(R/S‐PPA)4(n‐BA)6Ag2Bi4I24]·2H2O (2‐R and 2‐S) (R/S‐PPA=R/S–1‐phenylpropylamine; IPA=isopentylamine; n‐BA=n‐butylamine). Their inorganic skeletons are linked by binuclear {Bi2I10} and infinite chain {Ag2Bi2I14}∞, in which bismuth clusters and multiple coordination modes (e.g., tetrahedral AgI4 and octahedral AgI6) are introduced into the double perovskite system for the first time. This introduction induces distortion of the inorganic layer, which may facilitate the transfer of chirality from the chiral cations into achiral double perovskite skeletons. Further, circular dichroism measurements and circularly polarized light detection confirm their inherent chiral optical activities. In addition, 1‐S exhibits an ultralow X‐ray detection limit of 129.5 nGy s−1, which is 42‐fold lower than that of demands in regular medical diagnosis (5.5 µGy s−1). This study provides a pathway to construct novel type of lead‐free cluster‐based double perovskite derivatives.

Amplification of Dissymmetry for Circularly Polarized Photodetection by Cooperative Supramolecular Polymerization.

Circularly polarized photodetectors require chiral light absorption materials with high sensing efficiency and low costs. Here readily accessible point chirality has been introduced to dicyanostilbenes as the chiral source, facilitating remote chirality transfer to the π-aromatic core by cooperative supramolecular polymerization. The single-handed supramolecular polymers display powerful circularly polarized photodetection capability with a dissymmetry factor value as high as 0.83, superior to those of π-conjugated small molecules and oligomers. Strong chiral amplification occurs between the enantiopure sergeants and the achiral soldiers. The resulting supramolecular copolymers exhibit comparable photodetection efficiency to those of the homopolymeric ones, with a 90 % decrease in the enantiopure compound consumption. Therefore, cooperative supramolecular polymerization provides an effective yet economical avenue toward circularly polarized photodetection applications.

Amplification of Dissymmetry for Circularly Polarized Photodetection by Cooperative Supramolecular Polymerization

AbstractCircularly polarized photodetectors require chiral light absorption materials with high sensing efficiency and low costs. Here readily accessible point chirality has been introduced to dicyanostilbenes as the chiral source, facilitating remote chirality transfer to the π‐aromatic core by cooperative supramolecular polymerization. The single‐handed supramolecular polymers display powerful circularly polarized photodetection capability with a dissymmetry factor value as high as 0.83, superior to those of π‐conjugated small molecules and oligomers. Strong chiral amplification occurs between the enantiopure sergeants and the achiral soldiers. The resulting supramolecular copolymers exhibit comparable photodetection efficiency to those of the homopolymeric ones, with a 90 % decrease in the enantiopure compound consumption. Therefore, cooperative supramolecular polymerization provides an effective yet economical avenue toward circularly polarized photodetection applications.

Chiral Perovskite Nanoplatelets with Tunable Circularly Polarized Luminescence in the Strong Confinement Regime

AbstractChiral perovskite nanocrystals have emerged as an interesting chiral excitonic platform that combines both structural flexibility and superior optoelectronic properties. Despite several recent demonstrations of optical activity in various chiral perovskite nanocrystals, efficient circularly polarized luminescence (CPL) with tunable energies remains a challenge. The chirality imprinting mechanism as a function of perovskite nanocrystal dimensionality remains elusive. Here, atomically thin inorganic perovskite nanoplatelets (NPLs) are synthesized with precise control of layer thickness and are functionalized by chiral surface ligands, serving as a unique platform to probe the chirality transfer mechanism at the organic/perovskite interface. It is found that chirality is successfully imprinted into mono‐, bi‐, and tri‐layer inorganic perovskite NPLs, exhibiting tunable circular dichroism (CD) and CPL responses. However, chirality transfer decreases in thicker NPLs, resulting in decreased CD and CPL dissymmetry factors for thicker NPLs. Aided by large‐scale first‐principles calculations, it is proposed that chirality transfer is mainly mediated through a surface distortion rather than a hybridization of electronic states, giving rise to symmetry breaking in the perovskite lattice and spin‐split conduction bands. The findings described here provide an in‐depth understanding of chirality transfer and design principles for distorted‐surface perovskites for chiral photonic applications.

Dirhodium(II)/Phosphine Catalyst with Chiral Environment at Bridging Site and Its Application in Enantioselective Atropisomer Synthesis.

A dirhodium(II)/phosphine catalyst with a chiral environment at the bridging site was developed for the asymmetric arylation of phenanthrene-9,10-diones with arylboronic acids. In contrast to the classic chiral bridging carboxylic acid (or derivatives) ligand strategy of bimetallic dirhodium(II) catalysis, in this reaction, tuning both axial and bridging ligands realized the first Rh2(OAc)4/phosphine-catalyzed highly enantioselective carbonyl addition reaction. The kinetic analysis reveals that dirhodium(II) and arylboronic acid follow the first-order kinetics, while phenanthrene-9,10-dione is zeroth-order. These data supported the proposed catalytic cycle, where the key intermediate in the rate-determining step involved the dirhodium(II) complex and arylboronic acid. Finally, axially chiral biaryls were prepared based on a newly developed oxidative ring-opening reaction of α-hydroxyl ketones with a base and molecular oxygen, which featured a central-to-axial chirality transfer radical β-scission step.

One-Dimensional Chiral Copper Iodide Chain-Like Structure Cu4 I4 (R/S-3-quinuclidinol)3 with Near-Unity Photoluminescence Quantum Yield and Efficient Circularly Polarized Luminescence.

Chiral organic-inorganic hybrid metal halide materials have shown great potential for circularly polarized luminescence (CPL) related applications for their tunable structures and efficient emissions. Here, this work combines the highly emissive Cu4 I4 cubane cluster with chiral organic ligand R/S-3-quinuclidinol, to construct a new type of 1D Cu-I chains, namely Cu4 I4 (R/S-3-quinuclidinol)3 , crystallizing in noncentrosymmetric monoclinic P21 space group. These enantiomorphic hybrids exhibit long-term stability and show bright yellow emission with a photoluminescence quantum yield (PLQY) close to 100%. Due to the successful chirality transfer from the chiral ligands to the inorganic backbone, the enantiomers show intriguing chiroptical properties, such as circular dichroism (CD) and CPL. The CPL dissymmetry factor (glum ) is measured to be ≈4×10-3 . Time-resolved photoluminescence (PL) measurements show long averaged decay lifetime up to 10 µs. The structural details within the Cu4 I4 reveal the chiral nature of these basic building units, which are significantly different than in the achiral case. This discovery provides new structural insights for the design of high performance CPL materials and their applications in light emitting devices.

Host‐Guest Chemistry of Chiral MOFs for Multicolor Circularly Polarized Luminescence Including Room Temperature Phosphorescence

AbstractExploiting the chirality transfer and amplification in the hierarchical chiral systems by the visible and accurate structures is still a challenge. Herein, a pair of homochiral metal‐organic frameworks (MOFs) DCF‐12 and LCF‐12 with high rigidity and high porosity are synthesized via reticular chemistry. Interestingly, these two enantiomers can act as nano‐containers, in which four chromophores, covering acridine, pyrene, 9,10‐Bis(phenylvinyl) anthracene (BPEA), and coronene can be introduced by in situ encapsulation. Importantly, the precise single crystal structures of all guest‐loaded MOFs by X‐ray diffraction technique can be obtained smoothly. It not only clearly reveals the chirality transfer from chiral host framework to achiral guest emitters through space chirality transfer, but also circularly polarized luminescence can be achieved and modulated through the synergistic effect. Extraordinarily, both pyrene@DCF‐12 and pyrene@LCF‐12 exhibit fascinating multi‐color tunable room temperature phosphorescence (RTP) and dynamic circularly polarized luminescence. Besides, the RTP quantum yields of pyrene@DCF‐12 and pyrene@LCD‐12 are high up to 75.39% and 73.43%, which exceeds most of that of RTP materials. These results demonstrate that chiral MOFs can serve as an accurate platform to investigate the mechanism of chirality transfer and amplification and to prompt the development of CPL‐active materials.

Reductive Asymmetric Aza-Mislow-Evans Rearrangement by 1,3,2-Diazaphospholene Catalysis.

1,3,2-diazaphospholene hydrides (DAP-H) enable smooth conjugate reduction of polarized double bonds. The transiently formed phosphorus-enolate provides a potential platform for reductive α-functionalizations. In this respect, asymmetric C-heteroatom bond forming processes are synthetically appealing but remain elusive. We report a 1,3,2-diazaphospholene-catalyzed three-step cascade reaction of N-sulfinyl acrylamides comprised of conjugate reduction, [2,3]-sigmatropic aza-Mislow-Evans rearrangement and subsequent S-O bond cleavage. The obtained enantio-enriched α-hydroxy amides are formed in good yields and excellent enantiospecificity. The stereo-defined P-bound N,O-ketene aminal ensures an excellent transfer of chirality from the sulfur stereocenter to α-carbon. The transformation operates under mild conditions at ambient temperature. Moreover, DAP-H is a competent reductant for the cleavage of formed sulfenate ester, eliminating the extra step in traditional Mislow-Evans processes.

Reductive Asymmetric Aza‐Mislow‐Evans Rearrangement by 1,3,2‐Diazaphospholene Catalysis**

Abstract1,3,2‐diazaphospholene hydrides (DAP−H) enable smooth conjugate reduction of polarized double bonds. The transiently formed phosphorus‐enolate provides a potential platform for reductive α‐functionalizations. In this respect, asymmetric C‐heteroatom bond forming processes are synthetically appealing but remain elusive. We report a 1,3,2‐diazaphospholene‐catalyzed three‐step cascade reaction of N‐sulfinyl acrylamides comprised of conjugate reduction, [2,3]‐sigmatropic aza‐Mislow‐Evans rearrangement and subsequent S−O bond cleavage. The obtained enantio‐enriched α‐hydroxy amides are formed in good yields and excellent enantiospecificity. The stereo‐defined P‐bound N,O‐ketene aminal ensures an excellent transfer of chirality from the sulfur stereocenter to α‐carbon. The transformation operates under mild conditions at ambient temperature. Moreover, DAP−H is a competent reductant for the cleavage of formed sulfenate ester, eliminating the extra step in traditional Mislow‐Evans processes.

Induced CPL-Active Materials Based on Chiral Supramolecular Co-Assemblies.

Circularly polarized luminescence (CPL) has attracted much interest due to its potential applications on chiral photonic techniques and optoelectronic materials science. As known, dissymmetry factor (gem ) of CPL is one essential factor for evaluating the features of CPL-active materials. Much attention has focused on how to increase the gem value, which is one of the most important issues for CPL practical applications. Recently, more and more works have demonstrated that chiral supramolecular could provide the significant strategy to improve the gem value through the orderly helical superstructure of chiral building blocks. Normally, this kind of chiral supramolecular assembly process can be accompanied by chirality transfer and induction mechanism, which can promote the amplification effect on the induced CPL of achiral dyes. In this review, we fully summarized recent advances on the induced CPL-active materials of chiral supramolecular co-assemblies, their applications in circularly polarized organic light-emitting diodes (CP-OLEDs) and current challenges.

Tuning the Chiral Structures from Self-Assembled Carbohydrate Derivatives.

Carbohydrates have been regarded as one of the most ideally suited candidates for chirality study via self-assembly owning to their unique chemical structures, abundance, and sustainability. Much efforts have been devoted to design and synthesize diverse carbohydrate derivatives and self-assemble them into various supermolecular morphologies. Nevertheless, still inadequate attention is paid to deeply and comprehensively understand how the carbohydrate structures and self-assembly approaches affect the final morphologies and properties for future demands. Herein, to fulfill the need, a range of recently published studies relating to the chirality of carbohydrates is reviewed and discussed. Furthermore, to tune the chirality of carbohydrate-based structures on both molecular and superstructural levels via chirality transfer and chirality expression, the designing of the molecules and choosing of the proper approaches for self-assembly are elucidated.

Light-triggered Modulation of Supramolecular Chirality.

Dynamically controlling the supramolecular chirality is of great significance in development of functional chiral materials, which is thus essential for the specific function implementation. As an external energy input, light is remote and accurate for modulating chiral assemblies. In non-polarized light control, some photochemically reactive units (e. g., azobenzene, ɑ-cyanostilbene, spiropyran, anthracene) or photo-induced directionally rotating molecular motors were designed to drive chiral transfer or amplification. Besides, photoexcitation induced assembly based physical approach was also explored recently to regulate supramolecular chirality beyond photochemical reactions. In addition, circularly polarized light was applied to induce asymmetric arrangement of organic molecules and asymmetric photochemical synthesis of inorganic metallic nanostructures, in which both wavelength and handedness of circularly polarized light have effects on the induced supramolecular chirality. Although light-triggered chiral assemblies have been widely applied in photoelectric materials, biomedical fields, soft actuator, chiral catalysis and chiral sensing, there is a lack of systematic review on this topic. In this review, we summarized the recent studies and perspectives in the constructions and applications of light-responsive chiral assembled systems, aiming to provide better knowledge for the development of multifunctional chiral nanomaterials.

Architecture-Controllable Single-Crystal Helical Self-assembly of Small-Molecule Disulfides with Dynamic Chirality.

Beyond the common supramolecular helical polymers in solutions, controlling single-crystal helical self-assembly with precisely defined chirality and architectures has been challenging. Here, we report that simply merging static homochiral amino acids with dynamic chiral disulfides can produce a class of building blocks featuring supramolecular helical single-crystal self-assembly with unusual stereodivergency. Analysis of 20 single-crystal structures of 1,2-dithiolanes gives an atom-precision understanding of the chirality transfer from the molecular to supramolecular level, featuring homochiral and heterochiral helical supramolecular self-assembly in the solid state. The underlying structure-assembly relationship reveals that the synergistic interplay of intermolecular H-bonds and the 1,2-dithiolane ring with adaptive chirality plays a key role in determining the assembly pathway, also involving the effects of residue groups, substituents, molecular stacking, and solvents. The confinement effect in the solid state can stabilize the dynamic stereochemistry of disulfide bonds and selectively result in specific conformers that can minimize the energy of global supramolecular systems. We envision that these results represent a starting point to use dynamic chiral disulfide as a functional entity in supramolecular chemistry and may inspire a new class of supramolecular helical polymers with dynamic functions.

Brightening up Full-Color and White Circularly Polarized Luminescence through Chiral Induction and Circularly Polarized Light Excitation.

Preparation of chiral materials from achiral helical polymers has aroused great interest among researchers. In this work, chiral small molecules were utilized to accomplish chiral induction toward racemic helical polyacetylene via intermolecular π-π stacking by which chiral films with strong optical activity were fabricated. Furthermore, introducing fluorescent components generated full-color and white circularly polarized luminescence (CPL). A CPL generation mechanism is proposed accordingly, namely circularly polarized light excitation (CP-Ex). CPL emission and amplification of the luminescence dissymmetry factor were achieved under the synergetic effect of CP-Ex and chirality transfer. The CP-Ex mechanism was further verified by the double-layered film consisting of a chiral layer and a fluorescent layer. More noticeably, for double-layered films, the sense of CPL signals can be switched by changing the direction of excitation light. This work opens up new strategies for exploring tunable multiple- and white-color CPL materials.

Regulation of Chirality Transfer and Amplification from Chiral Cysteine to Gold Nanorod Assemblies using Nonchiral Surface Ligands

AbstractOwing to large chiroptical activity and high tunability, dynamic chiral superstructures of plasmonic nanoparticles have attracted great attention. A useful strategy has been developed to obtain strong plasmonic chiroptical responses (plasmonic circular dichroism, PCD) by adding small chiral thiols on achiral side‐by‐side assemblies of gold nanorods (AuNRs). Despite the critical role of chiral thiols, the impact of achiral surface ligands is yet to be revealed. Herein, the effects of achiral surface ligands are systematically investigated from the viewpoints of counter ion, hydrocarbon chain length, and head group of surfactants. A well‐packed ligand shell is found to be beneficial for the chirality transfer and amplification from adsorbed chiral thiols to rod assemblies. The PCD temperature amplification effect is observed by using different surfactant ligands and reflects the energy cost of rod‐twisting in the assemblies. This study deepens the understanding of chiral plasmonic assemblies driven by small chiral molecules and provides rational design to fabricate such assembly structures.

Construction of Axially Chiral Biaryls via Atroposelective ortho-C–H Arylation of Aryl Iodides

Due to the dichotomy between reactivity and stereoselectivity, the synthesis of axially chiral biaryls via enantioselective C–H arylation remains a daunting challenge. This full account describes the development of a general and modular platform for the construction of axial chirality through atroposelective ortho-C–H arylation of aryl iodides based on palladium/chiral norbornene cooperative catalysis. It is a three-component cascade process that involves readily available aryl iodides, 2,6-substituted aryl bromides, and various terminating reagents (e.g., olefins, alkynes, boronic acids, etc.) as building blocks. Key features of this method include broad functional group tolerance, high enantioselectivities, a distinct stereoinduction model, and good step economy and scalability. Notably, this method is also amenable for the synthesis of phenanthridinones with C–N axial chirality and chiral fluorenols through axial-to-axial and axial-to-central chirality transfer, respectively. Lastly, the origin of enantioselectivity in this method and the ortho-substituent effect of 2,6-substituted aryl bromides on stereoinduction are elucidated by density functional theory calculations.

Mechanistic Features of Asymmetric Vinylidene ortho-Quinone Methide Construction and Subsequent Transformations

Vinylidene ortho-quinone methide (VQM), an elusive dearomatized intermediate, is widely used in asymmetric catalysis. Due to its transient nature, the current understanding of VQM was largely acquired based on computational studies and trapping experiments. Herein, the enantioselective construction of stable VQM intermediates by an organocatalyzed bromination was achieved. Kinetic studies, control experiments, and nonlinear effects were realized to obtain insights into the two sequential mechanistic events in VQM-involved reactions. The results elucidated that the stereocontrol was enforced by one catalyst molecule in the generation of the axially chiral VQM, but the subsequent transformation was independent of the catalyst. The efficiency of the VQM as axially chiral synthetic reagents was demonstrated by its reactions with carboxylic acids, cyclo-1,3-diones, and nitrone. In all cases, the VQM reacted smoothly to provide the axially chiral esters and ethers via an axial-to-axial chirality transfer, as well as the chiral α-bromo ketones through an axial-to-central chirality conversion. The properties of the isolated VQM exhibited its high potential in organic chemistry.

Cascade Chirality Transfer Through Diastereomeric Interaction Enables Efficient Circularly Polarized Electroluminescence

AbstractOrganic light‐emitting diodes (OLEDs) with circularly polarized emission can bring a breakthrough innovation in display technologies. However, it remains challenging due to the difficulty in obtaining high efficiency and large dissymmetry factor simultaneously. Herein, it is demonstrated that robust circularly polarized (CP) electroluminescence can be induced by cascade chirality transfer within the emitting layer. Through spectroscopic data and theoretical analysis, the initiation of this chirality transfer process is assigned to diastereomeric interaction. Utilizing this interaction and excellent Förster resonance energy transfer ability to the well‐known racemic emitter, CP‐OLEDs with an electroluminescence dissymmetry factor (|gEL|) up to 3.2 × 10−3 and high external quantum efficiency (EQE) of 32% are successfully fabricated. These devices also show ultra‐low efficiency roll‐off at high brightness, with EQE ≥ 20% at 128 000 cd m−2. This study paves the way for the future development of CP‐OLEDs through synergistic materials and device engineering.

Large Optical Asymmetry in Silver Nanoparticle Assemblies Enabled by CH-π Interaction-Mediated Chirality Transfer.

Transfer of asymmetry from the molecular system to the other distinct system requires appropriate chemical interactions. Here, we show how the CH-π interaction, one of the weakest hydrogen bonds, can be applied to transfer the asymmetry from π-conjugated chiral molecules to the assemblies of plasmonic Ag nanoparticles, where the aliphatic chains of chiral molecules and the polystyrene chains grafted on Ag nanoparticles are served as the hydrogen donor and acceptor, respectively. The optical asymmetry g-factor of the chiral assemblies of plasmonic nanoparticles is strongly dependent on the molecular weight of the polystyrene ligand, the core structure of the molecule, and the aliphatic chain length of the chiral molecule. Importantly, we explore a molecular mixing strategy to enhance the asymmetry g-factor of chiral molecular assemblies, which consequently promotes the g-factor of chiral plasmonics efficiently, reaching a high value of ∼0.05 under optimal conditions. Overall, we rationalize the chirality transfer from chiral molecules to inorganic nanoparticles, providing the guidance for structural design of chiral nanocomposites with a high g-factor.

Strain-Driven Solid-Solid Crystal Conversion in Chiral Hybrid Pseudo-Perovskites with Paramagnetic-to-Ferromagnetic Transition.

Hybrid organic-inorganic perovskites (HOIPs) are promising stimuli-responsive materials (SPMs) owing to their molecular softness and tailorable structural dimensionality. The design of mechanically responsive HOIPs requires an in-depth understanding of how lattice strain induces intermolecular rearrangement that impacts physical properties. While chirality transfer from an organic cation to an inorganic lattice is known to influence chiral-optical properties, its effect on strain-induced phase conversion has not been explored. As opposed to achiral or racemic organic cations, chiral organic cations can potentially afford a new dimension in strain-responsive structural change. Herein, we demonstrate that mechanical strain induces a solid phase crystal conversion in chiral halide pseudo-perovskite single crystals (R/S)-(FE)2CuCl4 (FE = (4-Fluorophenyl)ethylamine) from a 0D isolated CuCl4 tetrahedral to 1D corner-sharing CuFCl5 octahedral framework via the incorporation of Cu···F interaction and N-H···F hydrogen bonding. This strain-induced crystal-to-crystal conversion involves the connection of neighboring 0D CuCl4 tetrahedra via Cu2+-Cl--Cu2+ linkages as well as the incorporation of a F-terminated organic cation as one of the X atoms in BX6 octahedra, leading to a reduced band gap and paramagnetic-to-ferromagnetic conversion. Control experiments using nonchiral or racemic perovskite analogs show the absence of such solid phase conversion. To demonstrate pressure-sensitive properties, the 0D phase is dispersed in water-soluble poly(vinyl alcohol) (PVA) polymer, which can be applied to a large-scale pressure-induced array display on fibrous Spandex substrates via a screen-printing method.