Precise Modulation of Circularly Polarized Luminescence via Polymer Chiral Co-assembly and Contactless Dynamic Chiral Communication.

Circularly polarized luminescence (CPL) plays a pivotal role in cutting-edge display and information technologies. Currently achieving precise color control and dynamic signal regulation in CPL still remains challenging due to the elusory relationship between fluorescence and chirality. Inspired by the natural mechanisms governing color formation and chiral interaction, we proposed an addition-subtraction principle theory to address this issue. Three fluorene-based polymers synthesized by Suzuki polycondensation with different electron-deficient monomers exhibit similar structures and UV/Vis absorption, but distinct fluorescence emissions due to intramolecular charge transfer. Based on this, precise-color CPL-active films are obtained through quantitative supramolecular co-assembly directed by addition principle. Particularly, an ideal white-emitting CPL film (CIE coordinates: (0.33, 0.33)) is facilely fabricated with a high quantum yield of 80.8 % and a dissymmetry factor (glum) of 1.4×10-2. Structural analysis reveals that the ordered stacking orientation favors higher glum. Furthermore, to address the dynamically regulated challenge, the comparable subtraction principle is proposed, involving a contactless chiral communication between excited and ground states. The representative system consisting of as-prepared fluorene-based polymers and chirality-selective absorption azobenzene (Azo)-containing polymers is constructed, achieving CPL weakening, reversal, and enhancement. Finally, a switchable quick response code is realized based on trans-cis isomerization of Azo moiety.

Switchable Phase Helicity Independent of the Absolute Configuration of the Stereocenter: Anomalous Induction between Sergeants and Soldiers in Chiral Liquid-Crystalline Polymers.

Controlling the secondary phase in chiral liquid-crystalline (LC) polymers is of great importance since it transfers and amplifies molecular information to the macroscopic properties. However, the chiral superstructures of the LC phase are determined exclusively by the inherent configuration of the parent chiral source. Here, we report the switchable supramolecular chirality of heteronuclear structures by the untraditional command between common chiral "sergeant" units and various achiral "soldier" units. Different chiral induction pathways between sergeants and soldiers were observed for copolymer assemblies with mesogenic and non-mesogenic soldier units, demonstrating the formation of a helical phase independent of the absolute configuration of the stereocenter. In the presence of non-mesogenic soldier units, the classical SaS (Sergeants and Soldiers) effect in the amorphous phase was observed; whereas in a full LC system, bidirectional command of sergeants was activated in response to the phase transition. Meanwhile, a full spectrum of morphological phase diagrams including spherical micelles, worms, nanowires, spindles, tadpoles, anisotropic ellipsoidal vesicles, and isotropic spherical vesicles were successfully achieved. Such spindles, tadpoles, and anisotropic ellipsoidal vesicles have rarely been obtained previously from chiral polymer systems.

Participation of Lattice Oxygen in Perovskite Oxide as a Highly Sensitive Sensor for p-Phenylenediamine Detection.

The harmful effects on the human body from p-phenylenediamine (PPD) in hair dyes can cause allergies and even cancer. Therefore, it is particularly important to accurately control and detect the content of PPD in our daily products and environment. Here, a small amount of non-metallic elemental P doped in perovskite oxide of SrCoO3-δ (SC) forms a good catalytic material, SrCo0.95P0.05O3-δ (SCP), for PPD detection. The improved performance compared with that of the parent SC can be attributed to three contributing factors, including a larger amount of highly oxidative oxygen species O22-/O-, better electrical conductivity, and more active sites on the P5+-oxygen bonds of SCP. Moreover, the lattice oxygen mechanism (LOM) with highly active species of lattice O vacancies and adsorbed -OO for electrocatalytic oxidation of PPD by the SCP/GCE (glass carbon electrode) sensor is proposed in our work. More importantly, the SCP/GCE sensor exhibits good stability, a low limit of detection, and high reliability (error < 5.78%) towards PPD determination in real samples of hair dyes, suggesting the substantial research potential for practical applications.

Simultaneous Chiral Fixation and Chiral Regulation Endowed by Dynamic Covalent Bonds.

The construction of chiral superstructures through the self-assembly of non-chiral polymers usually relies on the interplay of multiple non-covalent bonds, which is significantly limited by the memory ability of induced chirality. Although the introduction of covalent crosslinking can undoubtedly enhance the stability of chiral superstructures, the concurrent strong constraining effect hinders the application of chirality-smart materials. To address this issue, we have made a first attempt at the reversible fixation of supramolecular chirality by introducing dynamic covalent crosslinking into the chiral self-assembly of side-chain polymers. After chiral induction, the reversible [2+2] cycloaddition reaction of the cinnamate group in the polymer chains can be further controlled by light to manipulate inter-chain crosslinking and decrosslinking. Based on this photo-programmable and dynamic chiral fixation strategy, a novel pattern-embedded storage mechanism of chiral polymeric materials was established for the first time.

Fabrication and Decryption of a Microarray of Digital Dithiosuccinimide Oligomers.

Digital polymers with precisely arranged binary units provide an important option for information storage. This is especially true if the digital polymers are assembled in a device, as it would be of great benefit for data writing and reading in practice. Herein, inspired by the DNA microarray technique, the programmable information storing and reading on a mass spectrometry target plate is proposed. First, an array of 4-bit sequence-coded dithiosuccinimide oligomers is efficiently built through sequential thiol-maleimide Michael couplings with good sequence readability by tandem mass spectrometry (MS/MS). Then, toward engineering microarrays for information storage, a programmed robotic arm is specifically designed for precisely loading sequence-coded oligomers onto the target plate, and a decoding software is developed for efficient readout of the data from MS/MS sequencing. Notably, short sequence-coded oligomer chains can be used to write long strings of information, and extra error-correction codes are not required as usual due to the inherent concomitant fragmentation signals. Not only text but also bitimages can be automatically stored and decoded with excellent accuracy. This work provides a promising platform of digital polymers for programmable information storing and reading.

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.

Engineering Achiral Liquid Crystalline Polymers for Chiral Self-Recovery.

Flexible construction of permanently stored supramolecular chirality with stimulus-responsiveness remains a big challenge. Herein, we describe an efficient method to realize the transfer and storage of chirality in intrinsically achiral films of a side-chain polymeric liquid crystal system by combining chiral doping and cross-linking strategy. Even the helical structure was destroyed by UV light irradiation, the memorized chiral information in the covalent network enabled complete self-recovery of the original chiral superstructure. These results allowed the building of a novel chiroptical switch without any additional chiral source in multiple types of liquid crystal polymers, which may be one of the competitive candidates for use in stimulus-responsive chiro-optical devices.

Controlling the Multiple Chiroptical Inversion in Biphasic Liquid-Crystalline Polymers.

While controlling the chirality and modulating the helicity is a challenging task, it attracts great research interest for gaining a better understanding of the origin of chirality in nature. Herein, structurally similar azobenzene (Azo) vinyl monomers were designed in which the alkyl chains comprised the chiral stereocenter with different achiral tail lengths. Combining the synchronous polymerization, supramolecular stacking and self-assembly, the multiple chiroptical inversion of the Azo-polymer supramolecular assemblies can be modulated by the tail length and DP of Azo blocks during in situ polymerization. The DP-, UV light-, temperature-, aging time-dependent chiroptical properties and liquid-crystalline (LC) characterization indicated that the amorphous-to-LC phase transition and biphasic LC interconversion allow the transcription of intra-chain π-π stacking, inter-chain H- and J-aggregation, thereby controlling the dynamic multiple reversal of supramolecular chirality.

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.

Supramolecular Chirality in Azobenzene-Containing Polymer System: Traditional Postpolymerization Self-Assembly Versus In Situ Supramolecular Self-Assembly Strategy.

Recently, the design of novel supramolecular chiral materials has received a great deal of attention due to rapid developments in the fields of supramolecular chemistry and molecular self-assembly. Supramolecular chirality has been widely introduced to polymers containing photoresponsive azobenzene groups. On the one hand, supramolecular chiral structures of azobenzene-containing polymers (Azo-polymers) can be produced by nonsymmetric arrangement of Azo units through noncovalent interactions. On the other hand, the reversibility of the photoisomerization also allows for the control of the supramolecular organization of the Azo moieties within polymer structures. The construction of supramolecular chirality in Azo-polymeric self-assembled system is highly important for further developments in this field from both academic and practical points of view. The postpolymerization self-assembly strategy is one of the traditional strategies for mainly constructing supramolecular chirality in Azo-polymers. The in situ supramolecular self-assembly mediated by polymerization-induced self-assembly (PISA) is a facile one-pot approach for the construction of well-defined supramolecular chirality during polymerization process. In this review, we focus on a discussion of supramolecular chirality of Azo-polymer systems constructed by traditional postpolymerization self-assembly and PISA-mediated in situ supramolecular self-assembly. Furthermore, we will also summarize the basic concepts, seminal studies, recent trends, and perspectives in the constructions and applications of supramolecular chirality based on Azo-polymers with the hope to advance the development of supramolecular chirality in chemistry.

In Situ Controlled Construction of a Hierarchical Supramolecular Chiral Liquid-Crystalline Polymer Assembly.

Hierarchical supramolecular chiral liquid-crystalline (LC) polymer assemblies are challenging to construct in situ in a controlled manner. Now, polymerization-induced chiral self-assembly (PICSA) is reported. Hierarchical supramolecular chiral azobenzene-containing block copolymer (Azo-BCP) assemblies were constructed with π-π stacking interactions occurring in the layered structure of Azo smectic phases. The evolution of chirality from terminal alkyl chain to Azo mesogen building blocks and further induction of supramolecular chirality in LC BCP assemblies during PICSA is achieved. Morphologies such as spheres, worms, helical fibers, lamellae, and vesicles were observed. The morphological transition had a crucial effect on the chiral expression of Azo-BCP assemblies. The supramolecular chirality of Azo-BCP assemblies destroyed by 365 nm UV irradiation can be recovered by heating-cooling treatment; this dynamic reversible achiral-chiral switching can be repeated at least five times.

Topological Winding Number Change and Broken Inversion Symmetry in a Hofstadter's Butterfly.

Graphene's quantum Hall features are associated with a π Berry's phase due to its odd topological pseudospin winding number. In nearly aligned graphene-hexagonal BN heterostructures, the lattice and orientation mismatch produce a superlattice potential, yielding secondary Dirac points in graphene's electronic spectrum, and under a magnetic field, a Hofstadter butterfly-like energy spectrum. Here we report an additional π Berry's phase shift when tuning the Fermi level past the secondary Dirac points, originating from a change in topological winding number from odd to even when the Fermi-surface electron orbit begins to enclose the secondary Dirac points. At large hole doping inversion symmetry breaking generates a distinct hexagonal pattern in the longitudinal resistivity versus magnetic field and charge density. Major Hofstadter butterfly features persist up to ∼100 K, demonstrating the robustness of the fractal energy spectrum in these systems.

Graphene nanoelectromechanical systems as stochastic-frequency oscillators.

We measure the quality factor Q of electrically driven few-layer graphene drumhead resonators, providing an experimental demonstration that Q ∼ 1/T, where T is the temperature. We develop a model that includes intermodal coupling and tensioned graphene resonators. Because the resonators are atomically thin, out-of-plane fluctuations are large. As a result, Q is mainly determined by stochastic frequency broadening rather than frictional damping, in analogy to nuclear magnetic resonance. This model is in good agreement with experiment. Additionally, at larger drives the resonance line width is enhanced by nonlinear damping, in qualitative agreement with recent theory of damping by radiation of in-plane phonons. Parametric amplification produced by periodic thermal expansion from the ac drive voltage yields an anomalously large line width at the largest drives. Our results contribute toward a general framework for understanding the mechanisms of dissipation and spectral line broadening in atomically thin membrane resonators.

Revealing Pathway Complexity and Helical Inversion in Supramolecular Assemblies Through Solvent-Induced Radical Disparities.

New insights are raised to interpret pathway complexity in the supramolecular assembly of chiral triarylamine tris-amide (TATA) monomer. In cosolvent systems, the monomer undergoes entirely different assembly processes depending on the chemical feature of the two solvents. Specifically, 1,2-dichloroethane (DCE) and methylcyclohexane (MCH) cosolvent trigger the cooperative growth of monomers with M helical arrangement, and hierarchical thin nanobelts are further formed. But in DCE and hexane (HE) combination, a different pathway occurs where monomers go through isodesmic growth to generate twisted nanofibers with P helical arrangement. Moreover, the two distinct assemblies exhibit opposite excited-state chirality. The driving force for both assemblies is the formation of intermolecular hydrogen bonds between amide moieties. However, the mechanistic investigation indicates that radical and neutral triarylamine species go through distinct assembly phases by changing solvent structures. The neutralization of radicals in MCH plays a critical role in pathway complexity, which significantly impacts the overall supramolecular assembly process, giving rise to inversed supramolecular helicity and distinct morphologies. This differentiation in pathways affected by radicals provides a new approach to manipulate chiral supramolecular assembly process by facile solvent-solute interactions.

Self-recovery of chiral microphase separation in an achiral diblock copolymer system.

Macroscopic regulation of chiral supramolecular nanostructures in liquid-crystalline block copolymers is of great significance in photonics and nanotechnology. Although fabricating helical phase structures via chiral doping and microphase separation has been widely reported, the chiral memory and self-recovery capacity of asymmetric phase structures are the major challenge and still deeply rely on the presence of chiral additives. Herein, we demonstrate the first controllable chiral microphase separation in an achiral amphiphilic block copolymer consisting of poly(ethylene oxide) and azobenzene (Azo) groups. Chirality can be transferred to the fabricated helical nanostructures by doping with chiral additives (tartaric acid, TA). After the removal of the chiral additives and then performing cross-linking, the formed helical nanostructures will completely dispense with the chiral source. The supramolecular chirality and the micron-scale phase structure can be maintained under UV irradiation and heating-cooling treatment, enabling a reversible "on-off" chiroptical switch feature. This work is expected to avoid the tedious synthesis and expensive raw materials and shows a great application prospect in chiral separation and so on.

A natural polyphenol-functionalized chitosan/gelatin sponge for accelerating hemostasis and infected wound healing.

Natural polymers have been particularly appealing for constructing hemostatic materials/devices, but it is still desirable to develop new natural polymer-based biomaterials with balanced hemostatic and wound-healing performance. In this work, a natural polyphenol-functionalized chitosan/gelatin sponge (PCGS) was prepared by the lyophilization of a chitosan/gelatin mixture solution (under a self-foaming condition to prepare the CGS) and subsequent chemical cross-linking with procyanidin (PC). Compared with the original CGS, PCGS exhibited an enhanced liquid-absorption ability, reduced surface charges, and similar/low hemolysis rate. Benefiting from such a liquid-absorption ability (∼4000% for whole blood and normal saline) and moderate surface charges, PCGS exhibited high in vitro hemostatic property and promising hemostatic performance in an in vivo femoral-artery-injury model. In addition, PCGS possessed higher antioxidant property and slightly decreased antibacterial ability than CGS, owing to the incorporation of PC. The feasibility of PCGS for treating infected wounds was further confirmed in an in vivo infected-tooth-extraction model, as the typical complication of intractable tooth-extraction bleeding. The present work demonstrated a facile approach for developing multifunctional hemostatic materials through the flexible management of natural polymers and polyphenols.

Chiral Expression and Morphology Control in Polymer Dispersion Systems.

The chiral self-assembly of polymers in dispersions plays an important role in chiral chemistry and self-assembly. In general, both polymerization-induced self-assembly (PISA) and post-polymerization self-assembly can be used to prepare polymer nanoassemblies. In chirality induction or transfer processes, the self-assembly manner of the polymers greatly affects the chiral expression of the nanostructure and cannot be ignored in the chiral fields. Moreover, unique chiral expression and morphological transition of polymer assemblies in dispersions enable the preparation of advanced functional chiroptical materials. Herein, this Review discusses recent advances in chiral expression and morphology control in polymer dispersion systems, particularly the comparison between traditional post-polymerization self-assembly and in situ PISA strategies, to predict and advance chirality control in polymers.

Chiral Liquid Crystalline Elastomer for Twisting Motion without Preset Alignment of Mesogens.

A chiral liquid crystalline elastomer (CLCE) actuator is demonstrated. The solution-cast polydomain film of CLCE can twist upon order-disorder phase transition without any preset alignment of mesogens. The handedness of twisting is specific to the molecular chirality of the chiral dopant in the CLCE structure, while the degree of twisting, in terms of helical pitch and diameter, is sensitive to the aspect ratio and the thickness of the CLCE strip as well as the chiral dopant content. This phenomenon appears to stem from the local twisting forces and deformations of randomly oriented helical domains, which cannot cancel each other out due to the chirality and thus result in a macroscopic "chiral" force acting on the CLCE actuator. This finding reveals a materials design for preparing twisting LCE actuators.

Different phase-dominated chiral assembly of polyfluorenes induced by chiral solvation: axial and supramolecular chirality.

The introduction of chirality in an achiral system will not only help avoid the tedious and expensive synthesis of chiral substances or catalysts but also greatly expand the ranges of chiral compounds. Herein, the induction of chirality in achiral polyfluorene (PF2/6 and PF8) with different alkyl chains at the C9 position of fluorene was achieved using a binary solvent system, in which ethanol was used as a poor solvent and chiral limonene was employed simultaneously as a good solvent and chiral solvent. The circular dichroism (CD), UV-vis and photoluminescence (PL) spectra demonstrated that the structures of PFs with linear/branched alkyl side chains and the volume fractions of the cosolvents had an obvious effect on the generation of chirality driven by chiral solvation. During the chiral assembly processes of PFs, PF8 with a linear alkyl side chain demonstrated the obvious chiral ß phase, while PF2/6 with a branched alkyl side chain only showed the chiral α phase. WAXD data also confirmed the existence of quite different phases of PF8 and PF2/6. The first induced chirality of PF with a branched alkyl side chain (PF2/6) will help the further understanding of the chiral assembly mechanism of PFs driven by chiral solvation. The induced chirality of PF2/6 was axial chirality of the PF chain but the chirality of PF8 was from the supramolecular chiral assembly of the PF chains. The linear dependence of the maximum CD and g CD values on the enantiomeric purity of chiral limonene demonstrated that the achiral PFs have a potential application as chiral sensors to detect the ee value of limonene.

Synthesis and Photocontrolled Supramolecular Self-Assembly of Azobenzene-Functionalized Perylene Bisimide Derivatives.

Azobenzene (Azo) units were successfully introduced into perylene bisimide (PBI) structures in order to realize the photocontrolling of the morphology of the supramolecular assembly of PBI by a photoisomerization process. A total of three Azo-functionalized perylene bisimide derivatives (PBI1, PBI2, and PBI3) with different alkyl chain lengths were designed and synthesized by imidization of 3,4,9,10-perylene tetracarboxylic dianhydride with the corresponding amines. The structures of these compounds were characterized by proton nuclear magnetic resonance (1H NMR) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The photoisomerization behaviors of Azo units in PBIs were investigated using ultraviolet-visible (UV-VIS) absorption spectroscopy, which were obviously effected by solvents and the alkyl chain length. Furthermore, the photoisomerization of Azo units has the obviously regulatory effect on the morphology of supramolecular assembly of PBIs, especially for the medium-length alkyl chain-linked Azo-functionalized PBI derivative (PBI2). This research realized the photocontrolling of the morphology of the supramolecular assembly of PBI derivatives by photoisomerization of Azo units.