Chiral Imprinting Research Articles

Structural and Electronic Chirality in Inorganic Crystals: from Construction to Application.

Chirality represents a fundamental characteristic inherent in nature, playing a pivotal role in the emergence of homochirality and the origin of life. While the principles of chirality in organic chemistry are well-documented, the exploration of chirality within inorganic crystal structures continues to evolve. This ongoing development is primarily due to the diverse nature of crystal/amorphous structures in inorganic materials, along with the intricate symmetrical and asymmetrical relationships in the geometry of their constituent atoms. In this review, we commence with a summary of the foundational concept of chirality in molecules and solid states matters. This is followed by an introduction of structural chirality and electronic chirality in three-dimensional and two-dimensional inorganic materials. The construction of chirality in inorganic materials is classified into physical photolithography, wet-chemistry method, self-assembly, and chiral imprinting. Highlighting the significance of this field, we also summarize the research progress of chiral inorganic materials for applications in optical activity, enantiomeric recognition and chiral sensing, selective adsorption and enantioselective separation, asymmetric synthesis and catalysis, and chirality-induced spin polarization. This review aims to provide a reference for ongoing research in chiral inorganic materials and potentially stimulate innovative strategies and novel applications in the realm of chirality.

Homochiral π‐Rich Covalent Organic Frameworks Enabled Chirality Imprinting in Conjugated Polymers: Confined Polymerization and Chiral Memory from Scratch

AbstractOptically active π‐conjugated polymers (OACPs) have garnered increasing research interest for their resemblance to biological helices and intriguing chirality‐related functions. Traditional methods for synthesizing involve decorating achiral conjugated polymer architectures with enantiopure side substituents through complex organic synthesis. Here, we report a new approach: the templated synthesis of unsubstituted OACPs via supramolecularly confined polymerizations of achiral monomers within nanopores of 2D or 3D chiral covalent organic frameworks (CCOFs). We show that the chiral π‐rich nanospaces facilitate the in situ enantiospecific polymerization and self‐propagation, akin to nonenzymatic polymerase chain reaction (PCR) system, resulting in chiral imprinting. The stacked polymer chains are kinetically inert enough to memorize the chiral information after liberating from CCOFs, and even after treatment at temperature up to 200 °C. The isolated OACPs demonstrate robust enantiodiscrimination, achieving up to 85 % ee in separating racemic amino acids. This underscores the potential of utilizing CCOFs as templates for supramolecularly imprinting optical activity into CPs, paving the way for synthetic evolution and advanced functional exploration of OACPs.

Homochiral π-Rich Covalent Organic Frameworks Enabled Chirality Imprinting in Conjugated Polymers: Confined Polymerization and Chiral Memory from Scratch.

Optically active π-conjugated polymers (OACPs) have garnered increasing research interest for their resemblance to biological helices and intriguing chirality-related functions. Traditional methods for synthesizing involve decorating achiral conjugated polymer architectures with enantiopure side substituents through complex organic synthesis. Here, we report a new approach: the templated synthesis of unsubstituted OACPs via supramolecularly confined polymerizations of achiral monomers within nanopores of 2D or 3D chiral covalent organic frameworks (CCOFs). We show that the chiral π-rich nanospaces facilitate the in situ enantiospecific polymerization and self-propagation, akin to nonenzymatic polymerase chain reaction (PCR) system, resulting in chiral imprinting. The stacked polymer chains are kinetically inert enough to memorize the chiral information after liberating from CCOFs, and even after treatment at temperature up to 200 °C. The isolated OACPs demonstrate robust enantiodiscrimination, achieving up to 85 % ee in separating racemic amino acids. This underscores the potential of utilizing CCOFs as templates for supramolecularly imprinting optical activity into CPs, paving the way for synthetic evolution and advanced functional exploration of OACPs.

Chiral Multidentate Ligand Facilitating Perovskite Nanocrystals with Circularly Polarized Luminescence and Chiral Assembly

AbstractChiral ligand modification has emerged as a promising route to confer intrinsic chirality in perovskite nanocrystals (NCs), thereby imparting them with optically active properties and rendering great superiority in the next generation of circularly polarized luminescence. However, the functionalization of chiral ligand is not fully explored and the underlying mechanism governing chirality transfer remains elusive. Herein, tryptophan (Try), a naturally occurring chiral amino acid, is verified to serve as multidentate chiral ligands attaching on the surface of perovskite NCs. Such strong coordination favors the chirality imprinting on the electronic state of CsPbBr3, resulting in notable circular dichroism features and circularly polarized luminescence with a maximum glum of 2.3 × 10−3. It is intriguing that the intermolecular interaction between Try ligands anchored on two neighboring NCs contribute to chiral optical properties as well. The RDG‐NCI analysis have confirmed the hydrogen bond between the amine and carboxylic groups on chiral Try, which may drive the chiral assembly of perovskite NCs.

Electron-donating functional groups strengthen ligand-induced chiral imprinting on CsPbBr3 quantum dots

Chiral perovskite nanoparticles and films are promising for integration in emerging spintronic and optoelectronic technologies, yet few design rules exist to guide the development of chiral material properties. The chemical space of potential building blocks for these nanostructures is vast, and the mechanisms through which organic ligands can impart chirality to the inorganic perovskite lattice are not well understood. In this work, we investigate how the properties of chiral ammonium ligands, the most common organic ligand type used with perovskites, affect the circular dichroism of strongly quantum confined CsPbBr3 nanocrystals. We show that aromatic ammonium ligands with stronger electron-donating groups lead to higher-intensity circular dichroism associated with the lowest-energy excitonic transition of the perovskite nanocrystal. We argue that this behavior is best explained by a modulation of the exciton wavefunction overlap between the nanocrystal and the organic ligand, as the functional groups on the ligand can shift electron density toward the organic species-perovskite lattice interface to increase the imprinting.

Universal imprinting of chirality with chiral light by employing plasmonic metastructures

Chirality, either of light or matter, has proved to be very practical in biosensing and nanophotonics. However, the fundamental understanding of its temporal dynamics still needs to be discovered. A realistic setup for this are the so-called metastructures, since they are optically active and are built massively, hence rendering an immediate potential candidate. Here, we propose and study the electromagnetic-optical mechanism leading to chiral optical imprinting on metastructures. Induced photothermal responses create anisotropic permittivity modulations, different for left or right circularly polarized light, leading to temporal-dependent chiral imprinting of hot-spots, namely, “imprinting of chirality.” The above effect has not been observed yet, but it is within reach of modern experimental approaches. The proposed nonlinear chiroptical effect is general and should appear in any anisotropic material; however, we need to design a particular geometry for this effect to be strong. These new chiral time-dependent metastructures may lead to a plethora of 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.

Detection of Glucose Based on Noble Metal Nanozymes: Mechanism, Activity Regulation, and Enantioselective Recognition.

Glucose monitoring is essential to evaluate the degree of glucose metabolism disorders. The enzymatic determination has been the most widely used method in glucose detection because of its high efficiency, accuracy, and sensitivity. Noble metal nanomaterials (NMs, i.e., Au, Ag, Pt, and Pd), inheriting their excellent electronic, optical, and enzyme-like properties, are classified as noble metal nanozymes (NMNZs). As the NMNZs are often involved in two series of reactions, the oxidation of glucose and the chromogenic reaction of peroxide, here the chemical mechanism by employing NMNZs with glucose oxidase (GOx) and peroxidase (POD) mimicking activities is briefly summarized first. Subsequently, the regulation strategies of the GOx-like, POD-like and tandem enzyme-like activities of NMNZs are presented in detail, including the materials, size, morphology, composition, and the reaction condition of the representative NMs. In addition, in order to further mimic the enantioselectivity of enzyme, the design of NMNZs with enantioselective recognition of d-glucose and l-glucose by using different chiral compounds (DNA, amino acids, and cyclodextrins) and molecular imprinting is further described in this review. Finally, the feasible solutions to the existing challenges and a vision for future development possibilities are discussed.

Ligand Coverage and Exciton Delocalization Control Chiral Imprinting in Perovskite Nanoplatelets

Chiral perovskites have recently generated significant interest, yet little is known about how their chiro-optical properties arise. In this study, chiral methylammonium lead halide perovskite nanoplatelets (NPLs) with varied halide and ligand compositions are prepared by using direct synthetic methods. Circular dichroism (CD) and 1H NMR studies find a nonlinear relationship between the chiroptical properties and the ratio of chiral phenylethylammonium (PEA) to achiral octylamine (OA) ligands on the NPL surface. We use density functional theory (DFT) computations and a chiral imprinted particle-in-a-box model to rationalize the experimentally observed CD spectra, and we find that the saturation of the induced chirality depends on the size of the perovskite exciton relative to the size of the ligand moleclues. Temperature-dependent CD and 1H NMR studies, combined with DFT analysis, show that both the CD intensity and sign depend strongly on the structure and orientation of the ligands. This work reveals the complex nature of chiral imprinting in perovskite nanostructures and establishes a simple physical model for ligand-induced chiral imprinting to guide the further development of chiral materials.

Modeling Complex Solvent Effects on the Optical Rotation of Chiral Molecules: A Combined Molecular Dynamics and Density Functional Theory Study.

The challenge of assigning the absolute stereochemical configuration to a chiral compound can be overcome via accurate ab initio predictions of optical rotation, a sensitive molecular property that is further complicated by solvent effects. The solvent's "chiral imprint"-the transfer of the chirality from the solute to the surrounding achiral solvent-is explored here using conformational averaging and time-dependent density-functional theory. These complex solvent effects are taken into account via simple averaging over a molecular dynamics trajectory together with the explicit quantum mechanical consideration of the solvent molecules within the solute's cybotactic region and implicit modeling of the bulk solvent. We consider several axes along which the system's optical rotation varies, including the sampling of the dynamical trajectory, the quality of the one-electron basis set, and the use of continuum solvent models to account for bulk effects.

Encoding Chiral Molecular Information in Metal Structures.

The concept of encoding molecular information in bulk metals has been proposed over the past decade. The structure of various types of molecules, including enantiomers, can be imprinted in achiral substrates. Typically, to encode metals with chiral information, several approaches, based on chemical and electrochemical concepts, can be used. In this Minireview, recent achievements with respect to the development of such materials are discussed, including the entrapment of chiral biomolecules in metals, the chiral imprinting of metals, as well as the combination of imprinting with nanostructuring. The features and potential applications of these designer materials, such as chirooptical properties, enantioselective adsorption and separation, as well as their use for asymmetric synthesis will be presented. This will illustrate that the development of molecularly encoded metal structures opens up very interesting perspectives, especially in the frame of chiral technologies.

Chiral Perturbation Theory in the Environment with Chiral Imbalance

We discuss the description of chiral imbalance imprint in pion matter. It is based on the Chiral Perturbation Theory supplemented by medium induced chiral chemical potential in the covariant derivative. Such an implementation of chiral imbalance recently was explored in linear sigma model inspired by QCD. The relationship between two sigma models is examined. A possible experimental detection of chiral imbalance in charged pion decays inside the fireball is pointed out.

Magnetoelectrochemistry and Asymmetric Electrochemical Reactions

Magnetoelectrochemistry is a branch of electrochemistry where magnetic fields play a vital role in the oxidation and reduction process of the molecules. When it comes to spin-dependent electrochemistry (SDE), becomes a new paradigm. This work presents electrochemical response during the “chiral imprinting” on working electrodes and the effects of potentiostatic and galvanostatic methods. We explore the use of the SDE concept, which is implemented for chiral-ferromagnetic (CFM) hybrid working electrodes, and we compare various electrochemical parameters affecting the quality of deposition. We electrochemically co-deposited nickel (Ni) with a chiral compound (tartaric acid) in its enantiopure forms (L and D), which allows us to obtain a chiral co-deposited nickel-tartaric acid (Ni-LTA or Ni-DTA) working electrode.

In Situ Growth of Chiral Gold Nanoparticles in Confined Silica Nanotube.

We reported here that chiral gold nanoparticles can be In Situ created inside a confined chiral silica nanotube. A bolaamphiphilic L-glutamic acid was found to self-assemble into nanotube and transcribed its chirality into the silica through co-assembly with ATPS and TEOS. After removing the bolaamphiphile, "chiral" alignment of propylamine groups or "chiral imprint" remained inside the silica nanotube. NaAuCl₄ was absorbed into silica nanotube via electrostatic and coordination interaction with propylamine groups. After In Situ reducing with ascorbic acid, the gold nanoparticles were formed inside the nanotube, which exhibited chiral optical activity. Interestingly, the chirality of gold nanoparticles still remained even after removing the silica nanotube template with HF, proved that the "chiral imprint" is strongly "memorized" by the gold nanoparticles.

Modeling the Chiral Imprinting Response of Oriented Dipole Moments on Metal Nanostructures

Chiral plasmonics is a growing field because of its potential to produce high-performance biomolecule sensors and negative refractive index materials. Understanding and controlling molecular properties and their effect on the chiroptical coupling between chiral molecular films and metal nanostructures is thus vital for the future design of devices. Here we develop and apply a theoretical method to study that coupling. We first extend the three-dimensional finite-difference time-domain method to include chiral molecular layers with arbitrarily oriented induced dipole moments relative to the nanostructure’s surface. We then use the methodology to investigate the chiral imprinting response from molecularly coated nanospheres as a test of the method. Finally we study a gold nanocross array to understand how long- and short-range interactions between the chiral molecular layer and the nanoparticles affect their optical response.

Directing Charge Transfer in Quantum Dot Assemblies.

The optical and electronic properties of semiconductor quantum dots (QDs) make them attractive candidates for applications in photovoltaics, spintronics, photocatalysis, and optoelectronics. Understanding how to control the flow of charge in QD assemblies is essential for realizing novel applications. This Account explores some unique characteristics of charge transport in QD dyads, triads, and their assemblies. The emerging features of these assemblies that provide new opportunities to manipulate charge flow at the nanoscale are (1) cascading energy landscapes and band offsets to inhibit charge recombination, (2) electrostatic fields that direct charge flow through QD-QD and QD-conjugated polymer junctions, and (3) QD chirality and chiral imprinting that promotes vectorial electron and spin selective transport. Charge flow kinetics is determined by a combination of familiar electron transfer parameters (reaction free energy, reorganization energy, and electronic coupling), donor and acceptor electronic densities of states, and internal electric fields. Electron transfer and electronic structure theory, combined with kinetic modeling, place the measured kinetics of QD electron transfer donor-acceptor assemblies into a unified conceptual context. The experimental transfer rates measured in these systems depend upon structure and the internal electric fields that are present in the assemblies. A negatively charged donor and positively charged acceptor, for example, facilitates (inhibits) electron (hole) transfer, while an electric field of opposite orientation (reversal of charges) inhibits (promotes) electron (hole) transfer. These and other emerging rules that govern charge flow in NP assemblies provide a strategy to design the directionality and yield of interfacial charge transport. Chirality at the nanoscale can induce spin selective charge transport, providing new ways to direct charge (and spin) flow in QD assemblies. Magnetoresistance and magnetic conductive probe atomic force microscopy experiments show spin selective electron transport for chirally imprinted QD assemblies. Photoinduced electron transfer from achiral donor-QDs to chiral acceptor-QDs depends on the electron spin and chiroptical properties of the acceptor-QDs. These assemblies show transport characteristics that correlate with features of the QDs' circular dichroism spectra, presenting intriguing challenges to theory, and indicating that spectroscopic signatures may assist in the design and diagnosis of functional molecular assemblies. Theoretical and experimental studies of charge transport in well-defined QD assemblies are establishing design principles for vectorial charge transport and are also refining questions surrounding the mechanism and control of these processes. These intensified efforts are forging links between fundamental discoveries regarding mechanism and practical applications for these novel assembled nanostructures.

Spin-dependent electrochemistry: Enantio-selectivity driven by chiral-induced spin selectivity effect

Spin-Dependent Electrochemistry (SDE) is a new paradigm in electrochemistry where the electrochemical response of a chiral electrode|solution interface is studied as a function of spin-polarized current. In this work, the SDE concept is further developed exploring the use of the “chiral imprinting” concept, which is implemented in two different, complementary, ways i) a chiral compound in bulk solution to obtain chiral-induced spin selectivity effect at the ferromagnetic (FM) electrode surface ii) conversely, a chiral-ferromagnetic (CFM) hybrid working electrode is produced: nickel is electrochemically co-deposited with a chiral compound, L-ta or D-(−)-tartaric acid, which is added to the electrodeposition bath; this allows to obtain a chiral co-deposited nickel-tartaric acid (Ni-LTA or Ni-DTA) working electrode. As a further innovation, the ferromagnetic working electrode is prepared by direct Ni electrodeposition on the north, or south, pole of a permanent magnet. The electrochemical response of these two chiral imprinted systems is studied by comparing cyclic voltammetry (CV) curves. The latter are recorded in the potential range relevant to the Ni(III)/Ni(II) electrochemical equilibrium, and also in the presence of glucose in bulk solution. An impressive variation in peak potentials is found when comparing CVs recorded on the north, versus south, pole of the magnet (in particular, when the co-deposited CFM working electrode is used). These results are properly rationalized within the Chiral-Induced Spin Selectivity (CISS) effect.

Making Glycine Methyl Ester Chiral.

We demonstrate that the simple achiral amino acid glycine as its methyl ester inherits the chiral imprint of methyl lactate upon complexation, resulting in induced vibrational optical activity of the methylene C-H bonds. To mimic conditions of ice on comets that are considered long-term reaction as well as storage entities for (organic) molecules, we employ the matrix isolation technique in conjunction with vibrational circular dichroism spectroscopy and DFT computations. The observed chirality transfer is likely a key element for the realization of concepts rationalizing chirogenesis, that is, the generation of a chiral imbalance.

Sequential process of chiral imprinting and composite formation allows to produce electrooptically active poly(bis-EDOT)/hydroxypropyl cellulose

Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the promising conjugated polymeric materials for organic devices such as organic solar cell or organic electroluminescence display. Hydroxypropyl cellulose (HPC) is a product of chemical-modified cellulose. HPC shows liquid crystal at appropriate condition in solvents. HPC has been used for a binder of medicines and can be applied for green sustainable chemistry in materials science. In this study, poly(bis-(3,4-ethylenedioxythiophene)), abbreviated as poly(bis-EDOT), film is prepared in cholesteric liquid crystals with electrochemical polymerization. We employ a dimer of EDOT (bis-EDOT) as a monomer because bis-EDOT shows good affinity with liquid crystals and the linear shape of bis-EDOT allows pre-orientation in liquid crystal prior to polymerization. The polymer film thus prepared in cholesteric liquid crystals (CLC) shows characteristic circular dichroism (CD) derived from 3-D asymmetric super structure. This study demonstrates that polymerization of the linear-shaped bis-EDOT can effectively imprint 3-D asymmetric structure from HPC as a polymer CLC matrix and form conductive polymer/non-conductive polymer composite.

Imprinting Chirality onto the Electronic States of Colloidal Perovskite Nanoplatelets.

The direct synthesis of chiroptical organic-inorganic methylammonium lead bromide perovskite nanoplatelets that are passivated by R- or S-phenylethylammonium ligands is reported. The circular dichroism spectra can be divided into two components: (1) a region associated with a charge transfer transition between the ligand and the nanoplatelet, 300-350 nm, and (2) a region corresponding to the excitonic absorption maximum of the perovskite, 400-450 nm. The temperature- and concentration-dependent circular dichroism spectra indicate that the chiro-optical response arises from chiral imprinting by the ligand on the electronic states of the quantum-confined perovskite rather than chiral ligand-induced stereoselective aggregation.