Enantioselective synthesis of helical polydiacetylene by application of linearly polarized light and magnetic field

Enhanced Asymmetric Circularly Polarized Luminescence in Self-Organized Helical Superstructures Enabled by Macro-Chiral Liquid Crystal Quantum Dots

Circularly polarized luminescent (CPL) materials have garnered considerable interest for a variety of advanced optical applications including 3D imaging, data encryption, and asymmetric catalysis. However, the development of high-performance CPL has been hindered by the absence of simple synthetic methods for chiral luminescent emitters that exhibit both high quantum yields and dissymmetry factors. In this study, we present an innovative approach for the synthesis of macro-chiral liquid crystal quantum dots (Ch-QDs/LC) and their CPL performance enhancement through doping with 4-cyano-4'-pentylbiphenyl (5CB), thus yielding a CPL-emitting generator (CEG). The Ch-QDs/LCs were synthesized, and their surfaces functionalized with a chiral mesogenic ligand, specifically cholesteryl benzoate, anchored via a lipoic acid linker. Under the regulation of chiral 2S-Zn2+ coordination complexes, the chiral LC encapsulation process promotes coordinated ligand substitution, resulting in an exceptional quantum yield of 56.3%. This is accompanied by high absorption dissymmetry factor (gabs) and luminescence dissymmetry factor (glum) values ranging from 10-3 to 10-2, surpassing most reported dissymmetry factors by at least an order of magnitude. The modular Ch-QDs/LCs demonstrate the ability to transfer chirality to the surrounding medium efficiently and manifest macro-chiral characteristics within a nematic LC matrix. Utilizing Ch-QDs/LC as an effective CPL emitter within achiral 5CB matrices enabled the system to achieve a maximum glum value of 0.35. The resultant CEG device acted as a direct CPL source, initiating enantioselective photopolymerization.

Spin-related excited-state phenomena in photochemistry

The spin of electrons plays a vital role in chemical reactions and processes, and the excited state generated by the absorption of photons shows abundant spin-related phenomena. However, the importance of electron spin in photochemistry studies has been rarely mentioned or summarized. In this review, we briefly introduce the concept of spin photochemistry based on the spin multiplicity of the excited state, which leads to the observation of various spin-related photophysical properties and photochemical reactivities. Then, we focus on the recent advances in terms of light-induced magnetic properties, excited-state magneto-optical effects and spin-dependent photochemical reactions. The review aims to provide a comprehensive overview to utilize the spin multiplicity of the excited state in manipulating the above photophysical and photochemical processes. Finally, we discuss the existing challenges in the emerging field of spin photochemistry and future opportunities such as smart magnetic materials, optical information technology and spin-enhanced photocatalysis.

Supramolecular assembly of dendronized diacetylenes into thermoresponsive chiral fibers and their covalent fixation through topochemical polymerization

By combination of dendritic topological structures with photopolymerizable diacetylene, here we report on supramolecular chiral assembly of the dendronized diacetylenes in water. These dendronized diacetylenes are constituted with three-fold dendritic oligoethylene glycols (OEGs), bridged with a dipeptide from phenylalanine and glycine. These dendronized amphiphiles exhibit intensive propensity to aggregate in water and form helical fibers, which show characteristic thermoresponsive behavior with phase transition temperatures dominated by hydrophilicity of the dendritic OEGs. Topochemical polymerization of these supramolecular fibers through UV irradiation transfers them into the covalent helical dendronized polydiacetylenes. Chirality of these dendronized polydiacetylenes can be mediated through the thermally-induced phase transitions, but is also intriguingly dependent on vortex via stirring. Through stirring the solutions, chiralities of the dendronized polydiacetylenes are inverted, which can be reversibly recovered after keeping still the solution. Hydrogels are formed from these dendronized diacetylenes through concentration-enhanced interactions between the supramolecular fibers. Their mechanical properties can be greatly increased through thermally-enhanced interactions between the fibers with storage moduli increased from 20 Pa to a few hundred Pa. In addition, through photo-polymerization, the supramolecular fibers are transferred into covalent dendronized polydiacetylenes, and the corresponding hydrogels show much improved mechanical properties with storage moduli about 10 kPa.

Efficient Ultraviolet Circularly Polarized Luminescence in Zero-Dimensional Hybrid Cerium Bromides

Ultraviolet circularly polarized luminescence (UV-CPL) with high photon energy shows great potential in polarized light sources and stereoselective photopolymerization. However, developing luminescent materials with high UV-CPL performance remains challenging. Here, we report a pair of rare earth Ce3+-based zero-dimensional (0D) chiral hybrid metal halides (HMHs), R/S-(C14H24N2)2CeBr7, which exhibits characteristic UV emissions derived from the Ce 5d-4f transition. The compounds show simultaneously high photoluminescent quantum yields of (32-39)% and large luminescent dissymmetry factor (|glum|) values of (1.3-1.5)×10-2. Thus, the figures of merits of R/S-(C14H24N2)2CeBr7 are calculated to be (4.5-5.8)×10-3, which are superior to the reported UV-CPL emissive materials. Additionally, nearly 91 % of their PL intensities at 300 K can be well preserved at 380 K (LED operating temperature) without phase transition or decomposition, demonstrating the excellent structural and optical thermal stabilities of R/S-(C14H24N2)2CeBr7. Based on these enantiomers, the fabricated UV-emitting CP-LEDs exhibit high polarization degrees of ±1.0 %. Notably, the UV-CPL generated from the devices can significantly trigger the enantioselective photopolymerization of diacetylene with remarkable stereoselectivity, and consequently yield polymerized products with the anisotropy factors of circular dichroism (gCD) up to ±3.9×10-2, outperforming other UV-CPL materials and demonstrating their great potential as UV-polarized light sources.

Spectrum-Dependent Image Convolutional Processing via a Two-Dimensional Polarization-Sensitive Photodetector

Currently, the improvement in the processing capacity of traditional processors considerably lags behind the demands of real-time image processing caused by the advancement of photodetectors and the widespread deployment of high-definition image sensors. Therefore, achieving real-time image processing at the sensor level has become a prominent research domain in the field of photodetector technology. This goal underscores the need for photodetectors with enhanced multifunctional integration capabilities than can perform real-time computations using optical or electrical signals. In this study, we employ an innovative p-type semiconductor GaTe0.5Se0.5 to construct a polarization-sensitive wide-spectral photodetector. Leveraging the wide-spectral photoresponse, we realize three-band imaging within a wavelength range of 390-810 nm. Furthermore, real-time image convolutional processing is enabled by configuring appropriate convolution kernels based on the polarization-sensitive photocurrents. The innovative design of the polarization-sensitive wide-spectral GaTe0.5Se0.5-based photodetector represents a notable contribution to the domain of real-time image perception and processing.

Intense Left-handed Circularly Polarized Luminescence in Chiral Nematic Hydroxypropyl Cellulose Composite Films

Integrating optically active components into chiral photonic cellulose to fabricate circularly polarized luminescent materials has transformative potential in disease detection, asymmetric reactions, and anticounterfeiting techniques. However, the lack of cellulose-based left-handed circularly polarized light (L-CPL) emissions hampers the progress of these chiral functionalizations. Here, this work proposes an unprecedented strategy: incorporating a chiral nematic organization of hydroxypropyl cellulose with robust aggregation-induced emission luminogens to generate intense L-CPL emission. By utilizing N,N-dimethylformamide as a good solvent for fluorescent components and cellulose matrices, this work produces a right-handed chiral nematic structure film with a uniform appearance in reflective and fluorescent states. Remarkably, this system integrates a high asymmetric factor (0.51) and an impressive emission quantum yield (55.8%) into one fascinating composite. More meaningfully, this approach is versatile, allowing for the incorporation of luminogen derivatives emitting multicolored L-CPL. These chiral fluorescent films possess exceptional mechanical flexibility (toughness up to 0.9 MJ m-3) and structural stability even under harsh environmental exposures, making them promising for the fabrication of various products. Additionally, these films can be cast on the fabrics to reveal multilevel and durable anticounterfeiting capabilities or used as a chiral light source to induce enantioselective photopolymerization, thereby offering significant potential for diverse practical applications.

Pathway-Dependent Self-Assembly for Control over Helical Nanostructures and Topochemical Photopolymerization

Pathway-dependent self-assembly, in which a single building block forms two or more types of self-assembled nanostructures, is an important topic due to its mimic to the complexity in biology and manipulation of diverse supramolecular materials. Here, we report a pathway-dependent self-assembly using chiral glutamide derivatives (L or D-PAG), which form chiral nanotwist and nanotube through a cooperative slow cooling and an isodesmic fast cooling process, respectively. Furthermore, pathway-dependent self-assembly can be harnessed to control over the supramolecular co-assembly of PAG with a luminophore β-DCS or a photopolymerizable PCDA. Fast cooling leads to the co-assembled PAG/β-DCS nanotube exhibiting green circularly polarized luminescence (CPL), while slow cooling to nanofiber with blue CPL. Additionally, fast cooling process promotes the photopolymerization of PCDA into a red chiral polymer, whereas slow cooling inhibits the polymerization. This work not only demonstrates the pathway-dependent control over structural characteristics but also highlights the diverse functions emerged from the different assemblies.

Helical-caging enables single-emitted large asymmetric full-color circularly polarized luminescence

Colorful circularly polarized luminescence materials are desired for 3D displays, information security and asymmetric synthesis, in which single-emitted materials are ideal owing to self-absorption avoidance, evenly entire-visible-spectrum-covered photon emission and facile device fabrication. However, restricted by the synthesis of chiral broad-luminescent emitters, the realization and application of high-performing single-emitted full-color circularly polarized luminescence is in its infancy. Here, we disclose a single-emitted full-color circularly polarized luminescence system (spiral full-color emission generator), composed of whole-vis-spectrum emissive quantum dots and chiral liquid crystals. The system achieves a maximum luminescence dissymmetry factor of 0.8 and remains an order of 10-1 in visible region by tuning its photonic bandgap. We then expand it to a series of desired customized-color circularly polarized luminescence, build chiral devices and further demonstrate the working scenario in the photoinduced enantioselective polymerization. This work contributes to the design and synthesis of efficient chiroptical materials, device fabrication and photoinduced asymmetric synthesis.

Precise Detection, Control and Synthesis of Chiral Compounds at Single-Molecule Resolution

Chirality, as the symmetric breaking of molecules, plays an essential role in physical, chemical and especially biological processes, which highlights the accurate distinction among heterochiralities as well as the precise preparation for homochirality. To this end, the well-designed structure-specific recognizer and catalysis reactor are necessitated, respectively. However, each kind of target molecules requires a custom-made chiral partner and the dynamic disorder of spatial-orientation distribution of molecules at the ensemble level leads to an inefficient protocol. In this perspective article, we developed a universal strategy capable of realizing the chirality detection and control by the external symmetry breaking based on the alignment of the molecular frame to external stimuli. Specifically, in combination with the discussion about the relationship among the chirality (molecule), spin (electron) and polarization (photon), i.e., the three natural symmetry breaking, single-molecule junctions were proposed to achieve a single-molecule/event-resolved detection and synthesis. The fixation of the molecular orientation and the CMOS-compatibility provide an efficient interface to achieve the external input of symmetry breaking. This perspective is believed to offer more efficient applications in accurate chirality detection and precise asymmetric synthesis via the close collaboration of chemists, physicists, materials scientists, and engineers.

Temperature-Controlled Pathway Complexity in Self-Assembly of Perylene Diimide-Polydiacetylene Supramolecule

Self-assembly process represents one of the most powerful and efficient methods for designing functional nanomaterials. For generating optimal functional materials, understanding the pathway complexity during self-assembly is essential, which involves the aggregation of molecules into thermodynamically or kinetically favored pathways. Herein, a functional perylene diimide (PDI) derivative by introducing diacetylene (DA) chains (PDI-DA) is designed. Temperature control pathway complexity with the evolution of distinct morphology for the kinetic and thermodynamic product of PDI-DA is investigated in detail. A facile strategy of UV-induced polymerization is adopted to trap and capture metastable kinetic intermediates to understand the self-assembly mechanism. PDI-DA showed two kinetic intermediates having the morphology of nanosheets and nanoparticles before transforming into the thermodynamic product having fibrous morphology. Spectroscopic studies revealed the existence of distinct H- and J-aggregates for kinetic and thermodynamic products respectively. The polymerized fibrous PDI-DA displayed reversible switching between J-aggregate and H-aggregate.

Exploring the Circular Polarization Capacity from Chiral Cellulose Nanocrystal Films for a Photo-Controlled Chiral Helix of Supramolecular Polymers

Circularly polarized light (CPL) is key to asymmetric photochemistry as it could impart the chiral organization information into chemical products. Here, we demonstrate the circular polarization capacity of chiral cellulose nanocrystal (CNC) films to trigger photo-alignment of achiral supramolecular polymers into helical structures. Right-handed transmitted (T-) CPL was generated from self-assembled CNC films, which induced amorphous azobenzene (Azo) supramolecular polymers into chiral structures. The chiral induction effect of T-CPL is enhanced on Azo polymers with longer spacers. The absorptive dissymmetry factor (g_abs ) values of liquid-crystal supramolecular polymers can be amplified significantly (over 10 times) after T-CPL irradiation. Moreover, by integrating carbon dots into CNC films, CPL emission with a considerable luminescence dissymmetry factor (g_lum ) up to -0.66 was achieved, and it could be used for the photo-alignment of Azo polymers with high chiroptical properties. This work provides new insight for the photo modulation of supramolecular polymers by CPL-active materials.

Possible chemical and physical scenarios towards biological homochirality

The single chirality of biological molecules in terrestrial biology raises more questions than certitudes about its origin. The emergence of biological homochirality (BH) and its connection with the appearance of life have elicited a large number of theories related to the generation, amplification and preservation of a chiral bias in molecules of life under prebiotically relevant conditions. However, a global scenario is still lacking. Here, the possibility of inducing a significant chiral bias "from scratch", i.e. in the absence of pre-existing enantiomerically-enriched chemical species, will be considered first. It includes phenomena that are inherent to the nature of matter itself, such as the infinitesimal energy difference between enantiomers as a result of violation of parity in certain fundamental interactions, and physicochemical processes related to interactions between chiral organic molecules and physical fields, polarized particles, polarized spins and chiral surfaces. The spontaneous emergence of chirality in the absence of detectable chiral physical and chemical sources has recently undergone significant advances thanks to the deracemization of conglomerates through Viedma ripening and asymmetric auto-catalysis with the Soai reaction. All these phenomena are commonly discussed as plausible sources of asymmetry under prebiotic conditions and are potentially accountable for the primeval chiral bias in molecules of life. Then, several scenarios will be discussed that are aimed to reflect the different debates about the emergence of BH: extra-terrestrial or terrestrial origin (where?), nature of the mechanisms leading to the propagation and enhancement of the primeval chiral bias (how?) and temporal sequence between chemical homochirality, BH and life emergence (when?). Intense and ongoing theories regarding the emergence of optically pure molecules at different moments of the evolution process towards life, i.e. at the levels of building blocks of Life, of the instructed or functional polymers, or even later at the stage of more elaborated chemical systems, will be critically discussed. The underlying principles and the experimental evidence will be commented for each scenario with particular attention on those leading to the induction and enhancement of enantiomeric excesses in proteinogenic amino acids, natural sugars, and their intermediates or derivatives. The aim of this review is to propose an updated and timely synopsis in order to stimulate new efforts in this interdisciplinary field.

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.

Chiral Conjugated Thermally Activated Delayed Fluorescent Polymers for Highly Efficient Circularly Polarized Polymer Light-Emitting Diodes

Two novel chiral conjugated polymers R-P and S-P designed and synthesized from a pair of circularly polarized thermally activated delayed fluorescence (CP-TADF) enantiomers are presented in this work. The two polymers exhibited excellent TADF properties with small singlet-triplet energy gaps (ΔE_ST) of 0.045 and 0.061 eV and relatively high photoluminescence quantum yields (PLQYs) of 72 and 76%, respectively. Besides, intense mirror-image circularly polarized luminescence signals were detected from R-P and S-P in both solution and film states with dissymmetry factors (|g_lum|) of up to 1.9 × 10^-3. Furthermore, solution-processed circularly polarized polymer light-emitting diodes (CP-PLEDs) fabricated with R-P and S-P achieved high maximum external quantum efficiencies of 14.9 and 15.8% and high maximum brightness (L_max) of 8940 and 12,180 cd/m² with yellowish-green emission peaks at 546 and 544 nm, respectively. Moreover, intense circularly polarized electroluminescence signals with electroluminescence dissymmetry factors (g_EL) of -1.5 × 10^-3 and +1.6 × 10^-3 were detected from the CP-PLED devices fabricated with R-P and S-P, respectively.

Dendronized polydiacetylenes via photo-polymerization of supramolecular assemblies showing thermally tunable chirality

Transformation of supramolecular chiral assemblies into covalent polymers integrates characteristics of supramolecular chemistry together with covalent entities, leading to fabrication of covalent chiral materials through versatile supramolecular chiral assemblies. Here, we report supramolecular assembly of an amphiphilic dendronized 10,12-pentacosadiynoic amide (PCDA) in aqueous solutions to form twisted ribbons, which were transferred into covalent dendronized polydiacetylenes (PDAs) via photopolymerization. These supramolecular dendronized PCDA and the corresponding covalent dendronized PDAs showed unprecedent thermoresponsive properties. The thermally-induced dehydration and aggregations tuned reversibly their chiralities, which can be visually inspected through colour changes.

Polymerization-Induced Helicity Inversion Driven by Stacking Modes and Self-Assembly Pathway Differentiation

Regulating the mutual stacking arrangements is of great interest for understanding the origin of chirality at different hierarchical levels in nature. Different from molecular level chirality, the control and manipulation of hierarchical chirality in polymer systems is limited to the use of external factors as the energetically demanding switching stimulus. Herein, the first self-assembly strategy of polymerization-induced helicity inversion (PIHI), in which the controlled packing and dynamic stereomutation of azobenzene (Azo) building blocks are realized by in situ polymerization without any external stimulus, is reported. A multiple helicity inversion and intriguing helix-helix transition of polymeric supramolecular nanofibers occurs during polymerization, which is collectively confirmed to be mediated by the transition between functionality-oriented π-π stacking, H-, and J-aggregation. The studies further reveal that helicity inversion proceeds through a delicate interplay of the thermodynamically and kinetically controlled, pathway-dependent interconversion process, which should provide new insight into the origin and handedness control of helical nanostructures with desired chirality.

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.

Magneto-chiral anisotropy: From fundamentals to perspectives

The interplay between chirality and magnetic fields gives rise to a cross effect referred to as magneto-chiral anisotropy (MChA), which can manifest itself in different physical properties of chiral magnetized materials. The first experimental demonstration of MChA was by optical means with visible light. Further optical manifestations of MChA have been evidenced across most of the electromagnetic spectrum, from terahertz to X-rays. Moreover, exploiting the versatility of molecular chemistry toward chiral magnetic systems, many efforts have been made to identify the microscopic origins of optical MChA, necessary to advance the effect toward technological applications. In parallel, the replacement of light by electric current has allowed the observation of nonreciprocal electrical charge transport in both molecular and inorganic conductors as a result of electrical MChA (eMChA). MChA in other domains such as sound propagation, photochemistry, and electrochemistry are still in their infancy, with only a few experimental demonstrations, and offer wide perspectives for further studies with potentially large impact, like the understanding of the homochirality of life. After a general introduction to MChA, we give a complete review of all these phenomena, particularly during the last decade.

Transfer, Amplification, Storage, and Complete Self-Recovery of Supramolecular Chirality in an Achiral Polymer System

Supramolecular chirality and its complete self-recovery ability are highly mystical in nature and biological systems, which remains a major challenge today. Herein, we demonstrate that partially cross-linked azobenzene (Azo) units can be employed as the potential chiral trigger to fully heal the destroyed helical superstructure in achiral nematic polymer system. Combining the self-assembly of Azo units and terminal hydroxyl groups in polymer side chains allows the vapor-induced chiral nematic phase and covalent fixation of the superstructure via acetal reaction. The induced helical structure of Azo units can be stored by inter-chain cross-linking, even after removal of the chiral source. Most interestingly, the stored chiral information can trigger perfect chiral self-recovery (CSR) behavior after being destroyed by UV light, heat, and solvents. The results pave a new way for producing novel chiroptical materials with reversible chirality from achiral sources.

Rational Design of Diphenyldiacetylene-Based Fluorescent Materials Enabling a 365-nm Light-Initiated Topochemical Polymerization

Photopolymerization of diacetylenes usually requires stringent reaction conditions like high energy irradiation of 254-nm light or even γ-rays, which are generally harmful to the human body and thus mild conditions with lower energy irradiation are required. In this study, different diphenyldiacetylene (DPDA) derivatives were rationally designed followed by the investigation of their photopolymerization behavior. It was found that the para-substituted amino groups could render the absorption band of DPDA bathochromically shifted, ensuring a 365-nm light wavelength coverage. On this basis, an organogel system was constructed by chemically modifying cholesteryl and lipoic acid onto the DPDA moiety in aromatic solvents. Such uniform self-assemblies further facilitated to a rather high degree of polymerization by 365-nm irradiation. As a kind of fluorescent materials, the whole polymerization process of this system can be visualized by a photoluminescent signal.

Spin Filtering in Supramolecular Polymers Assembled from Achiral Monomers Mediated by Chiral Solvents

In past studies, spin selective transport was observed in polymers and supramolecular structures that are based on homochiral building blocks possessing stereocenters. Here we address the question to what extent chiral building blocks are required for observing the chiral induced spin selectivity (CISS) effect. We demonstrate the CISS effect in supramolecular polymers exclusively containing achiral monomers, where the supramolecular chirality was induced by chiral solvents that were removed from the fibers before measuring. Spin-selective transport was observed for electrons transmitted perpendicular to the fibers’ long axis. The spin polarization correlates with the intensity of the CD spectra of the polymers, indicating that the effect is nonlocal. It is found that the spin polarization increases with the samples’ thickness and the thickness dependence is the result of at least two mechanisms: the first is the CISS effect, and the second reduces the spin polarization due to scattering. Temperature dependence studies provide the first support for theoretical work that suggested that phonons may contribute to the spin polarization.

Biased Symmetry Breaking and Chiral Control by Self-Replicating in Achiral Tetradentate Platinum (II) Complexes

Obtaining homochirality from biased symmetry-breaking of self-assembly in achiral molecules remains a great challenge due to the lack of ingenious strategies and controlling their handedness. Here, we report the first case of biased symmetry breaking from achiral platinum (II) liquid crystals which self-organize into an enantiomerically enriched single domain without selection of handedness in twist grain boundary TGB ^[ *^] phase. Most importantly, the chiral control of self-organization can be achieved by using above the homochiral liquid crystal films with determined handedness (P or M) as a template. Moreover, benefiting from self-assembled superhelix, these complexes exhibit prominent circularly polarized luminescence with high |g_lum | up to 3.4×10^-3 in the TGB ^[ *^] mesophase. This work paves a neoteric avenue for the development of chiral self-assemblies from achiral molecules.

Circularly polarized luminescence from structurally coloured polymer films

Structurally coloured polymer films with circularly polarized luminescence (CPL) properties were prepared by the photopolymerization of cholesteric liquid crystal mixtures doped with aggregation-induced emission (AIE)-active tetraphenylethylene. The films show good CPL performance with the luminescence dissymmetry factor up to 0.58 and enhanced fluorescence efficiency.

Polymers with advanced structural and supramolecular features synthesized through topochemical polymerization

Polymers are an integral part of our daily life. Hence, there are constant efforts towards synthesizing novel polymers with unique properties. As the composition and packing of polymer chains influence polymer's properties, sophisticated control over the molecular and supramolecular structure of the polymer helps tailor its properties as desired. However, such precise control via conventional solution-state synthesis is challenging. Topochemical polymerization (TP), a solvent- and catalyst-free reaction that occurs under the confinement of a crystal lattice, offers profound control over the molecular structure and supramolecular architecture of a polymer and usually results in ordered polymers. In particular, single-crystal-to-single-crystal (SCSC) TP is advantageous as we can correlate the structure and packing of polymer chains with their properties. By designing molecules appended with suitable reactive moieties and utilizing the principles of supramolecular chemistry to align them in a reactive orientation, the synthesis of higher-dimensional polymers and divergent topologies has been achieved via TP. Though there are a few reviews on TP in the literature, an exclusive review showcasing the topochemical synthesis of polymers with advanced structural features is not available. In this perspective, we present selected examples of the topochemical synthesis of organic polymers with sophisticated structures like ladders, tubular polymers, alternating copolymers, polymer blends, and other interesting topologies. We also detail some strategies adopted for obtaining distinct polymers from the same monomer. Finally, we highlight the main challenges and prospects for developing advanced polymers via TP and inspire future directions in this area.

Solid-state colorimetric polydiacetylene liposome biosensor sensitized by gold nanoparticles

Polydiacetylene (PDA), a conjugated polymer, has attracted attention for realization of a label-free real-time colorimetric biosensor because it exhibits large and rapid colorimetric responses upon the binding of biomolecules. This is due to the conformational distortion of its conjugated backbone. However, solid-state PDA biosensors for point-of-care diagnosis remain unexplored. We describe a highly sensitive solid-state biosensor based on PDA liposomes. We employed gold nanoparticles (AuNPs) on PDA liposomes as the molecular-binding-signal sensitizer, which provides additional conformational distortion in the backbone structure of PDA by exerting steric repulsion to the attached biomolecules. To prove the concept, AuNPs and a thrombin-binding-aptamer were individually functionalized on PDA liposomes, which were attached to a substrate for the detection of thrombin. We found that the sensitivity was enhanced 2.5 times in the presence of AuNPs compared with the case without AuNPs. Because the steric repulsion of the AuNPs is target-independent, we believe that our solid-state biosensor provides a path toward advanced solid-state biosensors.

Induction, fixation and recovery of self-organized helical superstructures in achiral liquid crystalline polymer

A flexible chiral storage based on an achiral polymer system can be successfully achieved by chiral doping and covalent cross-linking.

Highly Sensitive Polydiacetylene Ensembles for Biosensing and Bioimaging

Polydiacetylenes are prepared from amphiphilic diacetylenes first through self-assembly and then polymerization. Different from common supramolecular assemblies, polydiacetylenes have stable structure and very special optical properties such as absorption, fluorescence, and Raman. The hydrophilic head of PDAs is easy to be chemically modified with functional groups for detection and imaging applications. PDAs will undergo a specific color change from blue to red, fluorescence enhancement and Raman spectrum changes in the presence of receptor ligands. These properties allow PDA-based sensors to have high sensitivity and specificity during analysis. Therefore, the PDAs have been widely used for detection of viruses, bacteria, proteins, antibiotics, hormones, sialic acid, metal ions and as probes for bioimaging in recent years. In this review, the preparation, polymerization, and detection mechanisms of PDAs are discussed, and some representative research advances in the field of bio-detection and bioimaging are highlighted.

Sequentially amplified circularly polarized ultraviolet luminescence for enantioselective photopolymerization

Chiral optical materials based on circularly polarized luminescence (CPL) have emerged rapidly due to their feasible applications in diverse fields of research. However, limited to the small luminescence dissymmetry factor (g_lum), real application examples have rarely been reported. Here, we present a complex system, which show intense circularly polarized ultraviolet luminescence (CPUVL) with large g_lum value, enabling a chiral UV light triggered enantioselective polymerization. By integrating sensitized triplet-triplet annihilation upconversion and CPL, both visible-to-UV upconversion emission and upconverted circularly polarized ultraviolet luminescence (UC-CPUVL) were obtained in the systems, built of chiral annihilator R(S)-4,12-biphenyl[2,2]paracyclophane (R-/S-TP), and a thermally activated delayed fluorescence (TADF) sensitizer. After dispersing this upconversion system into room-temperature nematic liquid crystal, induced chiral nematic liquid crystal could significantly amplify the g_lum value (0.19) of UC-CPUVL. Further, the UC-CPUVL emission has been used to trigger the enantioselective photopolymerization of diacetylene. This work paves the way for the further development of functional application of CPL active materials.

Circularly Polarized Luminescence in Nanoassemblies: Generation, Amplification, and Application

Currently, the development of circularly polarized luminescent (CPL) materials has drawn extensive attention due to the numerous potential applications in optical data storage, displays, backlights in 3D displays, and so on. While the fabrication of CPL-active materials generally requires chiral luminescent molecules, the introduction of the "self-assembly" concept offers a new perspective in obtaining the CPL-active materials. Following this approach, various self-assembled materials, including organic-, inorganic-, and hybrid systems can be endowed with CPL properties. Benefiting from the advantages of self-assembly, not only chiral molecules, but also achiral species, as well as inorganic nanoparticles have potential to be self-assembled into chiral nanoassemblies showing CPL activity. In addition, the dissymmetry factor, an important parameter of CPL materials, can be enhanced through various pathways of self-assembly. Here, the present status and progress of self-assembled nanomaterials with CPL activity are reviewed. An overview of the key factors in regulating chiral emission materials at the supramolecular level will largely boost their application in multidisciplinary fields.

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (g_abs and g_lum) and on the application of ECD and CPL to derive structural information on aggregated states.

Multifarious Chiral Nanoarchitectures Serving as Handed-Selective Fluorescence Filters for Generating Full-Color Circularly Polarized Luminescence

A series of full-color circularly polarized luminescence (CPL)-active materials are fabricated by judiciously combining multifarious chiral nanoarchitectures with achiral fluorescence dyes. The investigated nanoarchitectures include organic polymer nanofibers, organic-inorganic hybrid nanoflowers, and inorganic nanoflowers. The as-prepared chiral nanoarchitectures all can act as handed-selective fluorescence filters to powerfully transform unpolarized fluorescent light into circularly polarized luminescence. Also notable, no interaction is required between chiral and fluorescent components for achieving CPL emission. The present study provides a convenient and universal approach for preparing full-color CPL materials. Following the strategy, numerous chiroptical materials with CPL performance can be expected due to the abundant chiral matters and achiral fluorophores.

Highly enantioselective photo-polymerization enhanced by chiral nanoparticles and in situ photopatterning of chirality

Chiral noble metal nanoparticles has recently gained great interest due to their potential applications including ultrasensitive chiral recognition and asymmetric synthesis. We anticipate that they could be utilized to induce asymmetric photo-polymerization reactions with high enantioselectivity and reactivity. Here, we report such a system. By employing silver nanoparticles modified with cysteine as the chiral inducer, polydiacetylene (PDA) with high chiral asymmetry was obtained from achiral diacetylene monomers triggered with unpolarized UV light. Furthermore, the helical sense of chirality can be controlled by varying the wavelength of UV irradiation. This enables a feasible and economical method to fabricate programmable 2D patterns of chiral PDA with tailored chirality distributions, such as smooth gradients in chirality and micropatterns with tailorable circularly polarized luminescence. Our finding not only opens a pathway for producing programmable chiroptical micropatterns, but also is highly valuable for deeper understanding of symmetry breaking in enantioselective photochemical reactions.

Chiral nanoparticles are capable of ultrasensitive detection, characterization, and asymmetric synthesis of chiral organic and biological molecules. Here, the authors use silver nanoparticles modified with cysteine, as the sole chiral source, and unpolarized UV light, to form polydiacetylene with high chiral asymmetry from achiral diacetylene monomers.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

Homochiral Supramolecular Thin Film from Self-Assembly of Achiral Triarylamine Molecules by Circularly Polarized Light

Here, we report the formation of homochiral supramolecular thin film from achiral molecules, by using circularly polarized light (CPL) only as a chiral source, on the condition that irradiation of CPL does not induce a photochemical change of the achiral molecules. Thin films of self-assembled structures consisting of chiral supramolecular fibrils was obtained from the triarylamine derivatives through evaporation of the self-assembled triarylamine solution. The homochiral supramolecular helices with the desired handedness was achieved by irradiation of circularly polarized visible light during the self-assembly process, and the chiral stability of supramolecular self-assembled product was achieved by photopolymerization of the diacetylene moieties at side chains of the building blocks, with irradiation of circularly polarized ultraviolet light. This work provides a novel methodology for the generation of homochiral supramolecular thin film from the corresponding achiral molecules.

Recent advances in studies on the magneto-chiral dichroism of organic compounds

Magneto-chiral dichroism is described in terms of devices and synthesis, and is a clue to explain the homochirality of life.

Silylium cation initiated sergeants-and-soldiers type chiral amplification of helical aryl isocyanide copolymers

Silylium cations act as new highly efficient metal-free single-component cationic initiators for the cationic polymerization and copolymerization of chiral or achiral aryl isocyanides, preparing optically active polymers and copolymers obeying “sergeants-and-soldiers” rule.

Symmetry Breaking in Self-Assembled Nanoassemblies

The origin of biological homochirality, e.g., life selects the L-amino acids and D-sugar as molecular component, still remains a big mystery. It is suggested that mirror symmetry breaking plays an important role. Recent researches show that symmetry breaking can also occur at a supramolecular level, where the non-covalent bond was crucial. In these systems, equal or unequal amount of the enantiomeric nanoassemblies could be formed from achiral molecules. In this paper, we presented a brief overview regarding the symmetry breaking from dispersed system to gels, solids, and at interfaces. Then we discuss the rational manipulation of supramolecular chirality on how to induce and control the homochirality in the self-assembly system. Those physical control methods, such as Viedma ripening, hydrodynamic macro- and micro-vortex, superchiral light, and the combination of these technologies, are specifically discussed. It is hoped that the symmetry breaking at a supramolecular level could provide useful insights into the understanding of natural homochirality and further designing as well as controlling of functional chiral materials.

Optically Active Upconverting Nanoparticles with Induced Circularly Polarized Luminescence and Enantioselectively Triggered Photopolymerization

In this work, lanthanide-doped upconversion nanoparticles (UCNPs) showing upconverted circularly polarized luminescence were demonstrated in an organic-inorganic co-assembled system. Achiral UCNPs (NaYF₄:Yb/Er or NaYF₄:Yb/Tm) can be encapsulated into chiral helical nanotubes through the procedure of co-gelation. These co-gel systems display intense upconverted circularly polarized luminescence (UC-CPL) ranging from ultraviolet (UV, 300 nm) to near-infrared (NIR, 850 nm) wavelength. In addition, the UV part of UC-CPL can be used to initiate the enantioselective polymerization of diacetylene.

Towards homochiral supramolecular entities from achiral molecules by vortex mixing-accompanied self-assembly

Achieving homochirality is challenging both at the molecular and the supramolecular levels. While the origin of molecular homochirality still remains mysterious, the fabrication of homochiral assemblies from achiral molecules has attracted considerable interest since it provides many clues to understand the origin of molecular chirality. Here, by using a vortex mixing-accompanied self-assembly strategy, we obtained near-unity homochiral entities with controlled handedness from supramolecular gels that consist of exclusively achiral molecules without any chiral additives. The common supramolecular gelation process via heating and cooling of the achiral molecules only resulted in racemic gels. However, if vortex mixing is applied during the self-assembly, near-unity homochiral assemblies with uncontrolled handedness were obtained. Vortex mixing during the nucleation stage was found to be crucial in this case. On the other hand, if a small amount of the above vortex mixing produced assemblies was added as chiral seeds into the racemic gels, the racemic gels turned into near-unity homochiral suspensions with controlled handedness via a ripening process. Our studies provide an intriguing approach for achieving homochiral supramolecular assemblies from achiral molecules.

Chiral induction, modulation and locking in porphyrin based supramolecular assemblies with circularly polarized light

Herein, we propose a novel circularly polarized light (CPL) triggered asymmetric self-assembly strategy to controllably construct chiral supramolecular assemblies from achiral porphyrin derivatives.

Chiral nematic mesoporous silica films enabling multi-colour and on–off switchable circularly polarized luminescence

Chiral nematic mesoporous silica films encapsulating luminophores enabled R-CPL and multi-colour CPL with g_lum values of up to −0.38.