Nature-Inspired Chiral Structures: Fabrication Methods and Multifaceted Applications

Diverse chiral structures observed in nature find applications across various domains, including engineering, chemistry, and medicine. Particularly notable is the optical activity inherent in chiral structures, which has emerged prominently in the field of optics. This phenomenon has led to a wide range of applications, encompassing optical components, catalysts, sensors, and therapeutic interventions. This review summarizes the imitations and applications of naturally occurring chiral structures. Methods for replicating chiral architectures found in nature have evolved with specific research goals. This review primarily focuses on a top-down approach and provides a summary of recent research advancements. In the latter part of this review, we will engage in discussions regarding the diverse array of applications resulting from imitating chiral structures, from the optical activity in photonic crystals to applications spanning light-emitting devices. Furthermore, we will delve into the applications of biorecognition and therapeutic methodologies, comprehensively examining and deliberating upon the multifaceted utility of chiral structures.

Circularly Polarized Light Responsive Materials: Design Strategies and Applications

Circularly polarized light (CPL) with the end of optical vector traveling along circumferential trajectory shows left- and right-handedness, which transmits chiral information to materials via complicated CPL-matter interactions. Materials with circular dichroism respond to CPL illumination selectively with differential outputs that can be used to design novel photodetectors. Racemic or achiral compounds under CPL go through photodestruction, photoresolution, and asymmetric synthesis pathways to generate enantiomeric bias and optical activity. By this strategy, helical polymers and chiral inorganic plasmonic nanostructures are synthesized directly, and their intramolecular folding and subsequent self-assembly are photomodulable as well. In the aggregated state of self-assembly and liquid crystal phase, helical sense of the dynamic molecular packing is sensitive to enantiomeric bias brought by CPL, enabling the chiral amplification to supramolecular scale. In this review, the application-guided design strategies of CPL-responsive materials are aimed to be systematically summarized and discussed. Asymmetric synthesis, resolution, and property-modulation of small organic compounds, polymers, inorganic nanoparticles, supramolecular assemblies and liquid crystals are highlighted based on the important developments during the last decades. Besides, applications of light-matter interactions including CPL detection and biomedical applications are also referred.

Circularly Polarized Light-Enabled Chiral Nanomaterials: From Fabrication to Application

For decades, chiral nanomaterials have been extensively studied because of their extraordinary properties. Chiral nanostructures have attracted a lot of interest because of their potential applications including biosensing, asymmetric catalysis, optical devices, and negative index materials. Circularly polarized light (CPL) is the most attractive source for chirality owing to its high availability, and now it has been used as a chiral source for the preparation of chiral matter. In this review, the recent progress in the field of CPL-enabled chiral nanomaterials is summarized. Firstly, the recent advancements in the fabrication of chiral materials using circularly polarized light are described, focusing on the unique strategies. Secondly, an overview of the potential applications of chiral nanomaterials driven by CPL is provided, with a particular emphasis on biosensing, catalysis, and phototherapy. Finally, a perspective on the challenges in the field of CPL-enabled chiral nanomaterials is given.

Cascade energy transfer augmented circular polarization in photofluorochromic cholesteric texture

Circularly polarized luminescence (CPL)-active light-harvesting systems consisting of a light-responsive donor (R-1), mediator (Nile red), and terminal acceptor (Cyanine 5) are constructed in cholesteric liquid crystals. A dynamically tunable CPL dissymmetry factor and energy transfer modes, are achieved via the closed-ring and open-ring conversion between R-1-O and R-1-C.

Selectively Regulating the Chiral Morphology of Amino Acid-Assisted Chiral Gold Nanoparticles with Circularly Polarized Light

Chiral nanomaterials have attracted increasing attention due to their versatile optical properties. Although circularly polarized (CP) light can serve as an inducer, it has negligible effects because of the short lifetime of the plasmonic states. Here, we propose that the site-selective chirality regulation on the morphology of cysteine (cys) amino acid-assisted chiral gold nanoparticles (cys-chiral AuNPs) can be realized through CP light irradiation. This can result in the increased or decreased circular dichroism (CD) signal intensity. The site-selective growth mechanism of the cys-chiral AuNPs is elucidated with light-matter interactions through the opposite rotation of right(R)/left(L) CP light. The site-selective chirality growth of the cys-chiral AuNPs is ascribed to the morphology evolution induced by the synergy of cys and R/L-CP light, which is clearly analyzed and elucidated with high CD intensities. This work provides a promising alternative strategy to produce high-chirality nanomaterials that can be applied in biomedicine and enantiomer photocatalytic reaction.

Regulating the Excited State Chirality to Fabricate High-Performance-Solid-State Circularly Polarized Luminescence Materials

Developing solid-state materials and greatly improving the luminescence dissymmetry factors (g_lum) are the key issues for the future oriented practical application in the field of circularly polarized luminescence (CPL). However, most of the solid-state CPL-active materials suffer from aggregation caused emission quenching and relatively small g_lum values, which intensively restrict the development and application. In this work, high-performance CPL-active solid-state materials were achieved by regulating the excited state chirality of a series of bi-pyrene based chiral emitters. Due to the reversible mechanochromic luminescence under external stimuli, their excited state chirality can also be switched. It was found that the pristine amorphous powder possessed weak but obvious chiroptical properties because of the inherently chiral structures. Mechanical grinding could switch the fluorescence color and eliminate the CPL activity. Subsequently, by carrying out solvent fumigation, instant crystallization with well-defined microcrystal formation occurred, which could activate the CPL emission. Due to the chiral supramolecular arrangement of chromophores in the crystalline state, the resulting excimer emission in microcrystals showed chirality amplification not only in the excited state but also in the ground state. These findings not only provide a new method to fabricate high-performance CPL-active solid-state materials, but also clarify the chirality origin of pyrene-excimer-based chiral luminophores in various states which showed the importance of CPL as a probe of excited state chirality.

In situ instant crystallization significantly boosts the CPL performance in which both large circular polarization and high luminescence efficiency are achieved due to the chiral supramolecular arrangement of chromophores in the crystalline state.

A polymerization-induced gelation process visualized by nontraditional clustering-triggered emission

A kind of organogel with distinct CTE properties was synthesized via a PISA process. Fluorescence variation could be employed to realize the visualization of the PISA process according to the CTE mechanism.

Circularly Polarized Light-Driven Supramolecular Chirality

Introduction of asymmetry into a supramolecular system via external chiral stimuli can contribute to the understanding of the intriguing homochirality found in nature. Circularly polarized light (CPL) is regarded as a chiral physical force with right- or left-handedness. It can induce and modulate supramolecular chirality due to preferential interaction with one enantiomer. Herein, this review focuses on the photon-to-matter chirality transfer mechanisms at the supramolecular level. Thus, asymmetric photochemical reactions are reviewed, and the creation of a chiral bias upon CPL irradiation is discussed. Furthermore, the possible mechanisms for the amplification and propagation of the bias into the supramolecular level are outlined based on the nature of the photochromic building block. Representative examples, including azobenzene derivatives, polydiacetylene, bicyclic ketone, polyfluorenes, C_n -symmetric molecules, and inorganic nanomaterials, are presented.

Silica covering driven intensity enhancement and handedness inversion of the CPL signals of the supramolecular assemblies

Dipeptide-based hybrid materials with enhanced and inversed circularly polarized luminescence signals were fabricated through a dynamic supramolecular templating approach.

Improved enantioselectivity in thiol–ene photopolymerization of sulphur-containing polymers with circularly polarized luminescence

Optically active poly(thioether) are obtained based on CPL-triggered thiol–ene photopolymerization assisted with achiral HAD. The poly(thioether) exhibits clusterization-triggered emission and circularly polarized luminescence behavior.

The Chirality Induction and Modulation of Polymers by Circularly Polarized Light

Chirality is a natural attribute nature of living matter and plays an important role in maintaining the metabolism, evolution and functional activities of living organisms. Asymmetric conformation represents the chiral structure of biomacromolecules in living organisms on earth, such as the L-amino acids of proteins and enzymes, and the D-sugars of DNA or RNA, which exist preferentially as one enantiomer. Circularly polarized light (CPL), observed in the formation regions of the Orion constellation, has long been proposed as one of the origins of single chirality. Herein, the CPL triggered asymmetric polymerization, photo-modulation of chirality based on polymers are described. The mechanisms between CPL and polymers (including polydiacetylene, azobenzene polymers, chiral coordination polymers, and polyfluorene) are described in detail. This minireview provides a promising flexible asymmetric synthesis method for the fabrication of chiral polymer via CPL irradiation, with the hope of obtaining a better understanding of the origin of homochirality on earth.

Bacterial Cellulose: A Versatile Chiral Host for Circularly Polarized Luminescence

Materials capable of circularly polarized luminescence (CPL) have attracted considerable attention for their promising potential applications. Bacterial cellulose (BC) was characterized as having a stable right-handed twist, which makes it a potential chiral host to endow luminophores with CPL. Then, the CPL-active BC composite film was constructed by simply impregnating bacterial cellulose pellicles with dilute aqueous solutions of luminophores (rhodamine B, carbon dots, polymer dots) and drying under ambient conditions. Simple encapsulation of luminophores renders BC with circularly polarized luminescence with a dissymmetry factor of up to 0.03. The multiple chiral centers of bacterial cellulose provide a primary asymmetric environment that can be further modulated by supramolecular chemistry, which is responsible for its circular polarization ability. We further demonstrate that commercial grade paper may endow luminophores with CPL activity, which reifies the universality of the method.

Enantioselective cytotoxicity of chiral polymer vesicles with linear and hyperbranched structures

Herein, we study the enantioselective cytotoxicity of vesicles self-assembled by optically active linear polymers (LNPs) and hyperbranched polymers (HBPs). Compared to HBP vesicles, LNP vesicles exhibit properties such as a higher surface charge density and more violent interaction with simulated biomembranes which results in larger cytotoxicity against HeLa cells. Specifically, racemic-LNP vesicles exhibit the largest cytotoxicity of all. More interestingly, there is no significant enantioselective dependence of HBP vesicles on the abovementioned properties. Overall, we proved that the cytotoxicity of vesicles is deeply related to chirality and topological-structures. This research is of great fundamental value for the design of novel bio-interface materials.

Circularly Polarized Light with Sense and Wavelengths To Regulate Azobenzene Supramolecular Chirality in Optofluidic Medium

Circularly polarized light (CPL) as a massless physical force causes absolute asymmetric photosynthesis, photodestruction, and photoresolution. CPL handedness has long been believed to be the determining factor in the resulting product's chirality. However, product chirality as a function of the CPL handedness, irradiation wavelength, and irradiation time has not yet been studied systematically. Herein, we investigate this topic using achiral polymethacrylate carrying achiral azobenzene as micrometer-size aggregates in an optofluidic medium with a tuned refractive index. Azobenzene chirality with a high degree of dissymmetry ratio (±1.3 × 10^-2 at 313 nm) was generated, inverted, and switched in multiple cycles by irradiation with monochromatic incoherent CPL (313, 365, 405, and 436 nm) for 20 s using a weak incoherent light source (≈ 30 μW·cm^-2). Moreover, the optical activity was retained for over 1 week in the dark. Photoinduced chirality was swapped by the irradiating wavelength, regardless of whether the CPL sense was the same. This scenario is similar to the so-called Cotton effect, which was first described in 1895. The tandem choice of both CPL sense and its wavelength was crucial for azobenzene chirality. Our experimental proof and theoretical simulation should provide new insight into the chirality of CPL-controlled molecules, supramolecules, and polymers.