Photoexcitation-Induced Assembly: A Bottom-Up Physical Strategy for Driving Molecular Motion and Phase Evolution.

ConspectusIn the field of molecular assembly, photodriven self-assembly is a smart and crucial strategy to regulate the molecular orderliness, multiscale structure, and optoelectronic properties. Traditionally, photodriven self-assembly is based on photochemical processes, through molecular structural change induced by photoreactions. Despite great progress in the photochemical self-assembly, there still exists disadvantages (e.g., the photoconversion rate never reaches 100% with the possible side reactions). Therefore, the photoinduced nanostructure and morphology are often difficult to predict due to insufficient phase transition or defects. In contrast, the physical processes based on photoexcitation are straightforward and can fully utilize photons to avoid the drawbacks of photochemistry. The photoexcitation strategy excludes the change of molecular structure, only utilizing the molecular conformational change from the ground state to excited state. Then, the excited state conformation is employed to drive molecular movement and aggregation, further promoting the synergistic assembly or phase transition of the entire material system. The regulation and exploration of molecular assembly upon photoexcitation can open up a new paradigm to deal with the "bottom-up" behavior and develop unprecedented optoelectronic functional materials.This Account starts with a brief introduction to the problems faced by photocontrolled self-assembly and presents the photoexcitation-induced assembly (PEIA) strategy. Then, we focus on exploring PEIA strategy based on persulfurated arenes as the prototype. The molecular conformational transition of persulfurated arenes from the ground state to the excited state is conducive to the formation of intermolecular interactions, successively driving molecular motion, aggregation, and assembly. Next, we describe our progress in exploring PEIA of persulfurated arenes at the molecular level and then demonstrate that the PEIA of persulfurated arenes can synergistically drive molecular motion and phase transition in various block copolymer systems. Moreover, we provide the potential applications of PEIA in dynamic visual imaging, information encryption, and surface property regulation. Finally, an outlook on further development of PEIA is prospected.

On the fluid drag reduction in scallop surface.

In the field of biomimetics, the tiny riblet structures inspired by shark skin have been extensively studied for their drag reduction properties in turbulent flows. Here, we show that the ridged surface texture of another swimming creature in the ocean, i.e., the scallops, also has some friction drag reduction effect. In this study, we investigated the potential drag reduction effects of scallop shell textures using computational fluid dynamics simulations. Specifically, we constructed a conceptual model featuring an undulating surface pattern on a conical shell geometry that mimics scallop. Simulations modeled turbulent fluid flows over the model inserted at different orientations relative to the flow direction. The results demonstrate appreciable friction drag reduction generated by the ribbed hierarchical structures encasing the scallop, while partial pressure drag reduction exhibits dependence on alignment of scallop to the predominant flow direction. Theoretical mechanisms based on classic drag reduction theory in turbulence was established to explain the drag reduction phenomena. Given the analogous working environments of scallops and seafaring vessels, these findings may shed light on the biomimetic design of surface textures to enhance maritime engineering applications. Besides, this work elucidates an additional evolutionary example of fluid drag reduction, expanding the biological repertoire of swimming species.

Construction of Carbon Dots@LiCl-polyacrylamide with Humidity-Induced Ultralong Room-Temperature Phosphorescence to Fluorescence and Rigid-to-Flexible Transition Behavior.

The continuous advancement of luminescent materials has placed increasingly stringent requirements on dynamic color-tunable ultralong room-temperature phosphorescence (URTP) materials that can respond to external stimuli. Nevertheless, endowing URTP materials with stimuli-response-induced dynamic color tuning is a challenging task. This study introduces a carbon dots (CDs)@LiCl-polyacrylamide (PAM) polymer system that switches from URTP to fluorescence under humidity stimuli, accompanied by a transition from rigidity to flexibility. The obtained rigid CDs@LiCl-PAM exhibits ultralong green phosphorescence with a lifetime of 560 ms in the initial state. After absorbing moisture, it becomes flexible and its phosphorescence switches off. Moreover, the emission of the CDs@LiCl-PAM film depends on the excitation wavelength. This property can potentially used in multicolored luminescence applications and displays. Moreover, multicolor luminescent patterns can be constructed in situ using the water-absorption ability of the obtained thin film and the Förster resonance energy-transfer strategy. The proposed strategy is expected to promote the interdisciplinary development of intelligent information encryption, anti-counterfeiting, and smart flexible display materials.

Two polyketide synthase genes VpPKS10 and VpPKS33 regulated by VpLaeA are essential to the virulence of Valsa pyri.

Valsa pyri, the causal agent of pear canker disease, typically induces cankers on the bark of infected trees and even leads to tree mortality. Secondary metabolites (SMs) produced by pathogenic fungi play a crucial role in the pathogenic process. In this study, secondary metabolic regulator VpLaeA was identified in V. pyri. VpLaeA was found to strongly affect the pathogenicity, fruiting body formation and toxicity of SMs of V. pyri. Additionally, VpLaeA was also found to be required for the response of V. pyri to some abiotic stresses. Transcriptome data analysis revealed that many of differentially expressed genes were involved in the secondary metabolite biosynthesis (SMB). Among them, about one third of SMB core genes were regulated by VpLaeA at different periods. Seven differentially expressed SMB core genes (VpPKS9, VpPKS10, VpPKS33, VpNRPS6, VpNRPS7, VpNRPS16, and VpNRPS17) were selected for knockout. Two modular polyketide synthase (PKS) genes (VpPKS10 and VpPKS33), which were closely related to the virulence of V. pyri from the above seven genes were identified. Notably, VpPKS10 and VpPKS33 also affected the production of fruiting body of V. pyri, but didn't participate in the resistance of V. pyri to abiotic stresses. Overall, this study demonstrates the multifaceted biological functions of VpLaeA in V. pyri, and identifies two toxicity-associated PKS genes in Valsa species fungi for the first time.

Advances in photothermal regulation strategies: from efficient solar heating to daytime passive cooling.

Photothermal regulation concerning solar harvesting and repelling has recently attracted significant interest due to the fast-growing research focus in the areas of solar heating for evaporation, photocatalysis, motion, and electricity generation, as well as passive cooling for cooling textiles and smart buildings. The parallel development of photothermal regulation strategies through both material and system designs has further improved the overall solar utilization efficiency for heating/cooling. In this review, we will review the latest progress in photothermal regulation, including solar heating and passive cooling, and their manipulating strategies. The underlying mechanisms and criteria of highly efficient photothermal regulation in terms of optical absorption/reflection, thermal conversion, transfer, and emission properties corresponding to the extensive catalog of nanostructured materials are discussed. The rational material and structural designs with spectral selectivity for improving the photothermal regulation performance are then highlighted. We finally present the recent significant developments of applications of photothermal regulation in clean energy and environmental areas and give a brief perspective on the current challenges and future development of controlled solar energy utilization.

Engineering Tunable Ratiometric Dual Emission in Single Emitter-based Amorphous Systems.

Molecular emitters with multi-emissive properties are in high demand in numerous fields, while these properties basically depend on specific molecular conformation and packing. For amorphous systems, special molecular arrangement is unnecessary, but it remains challenging to achieve such luminescent behaviors. Herein, we present a general strategy that takes advantage of molecular rigidity and S1 -T1 energy gap balance for emitter design, which enables fluorescence-phosphorescence dual-emission properties in various solid forms, whether crystalline or amorphous. Subsequently, the amorphism of the emitters based polymethyl methacrylate films endowed an in situ regulation of the dual-emissive characteristics. With the ratiometric regulation of phosphorescence by external stimuli and stable fluorescence as internal reference, highly controllable luminescent color tuning (yellow to blue including white emission) was achieved. There properties together with a persistent luminous behavior is of benefit for an irreplaceable set of optical information combination, featuring an ultrahigh-security anti-counterfeiting ability. Our research introduces a concept of eliminating the crystal-form and molecular-conformational dependence of complex luminescent properties through emitter molecular design. This has profound implications for the development of functional materials.

Highly Efficient Room-Temperature Light-Induced Synthesis of Polymer Dots: A Programming Control Paradigm of Polymer Nanostructurization from Single-Component Precursor.

Polymer dots (PDs) have raised considerable research interest due to their advantages of designable nanostructures, high biocompatibility, versatile photoluminescent properties, and recyclability as nanophase. However, there remains a lack of in situ, real-time, and noncontact methods for synthesizing PDs. Here we report a rational strategy to synthesize PDs through a well-designed single-component precursor (an asymmetrical donor-acceptor-donor' molecular structure) by photoirradiation at ambient temperature. In contrast to thermal processes that normally lack atomic economy, our method is mild and successive, based on an aggregation-promoted sulfonimidization triggered by photoinduced delocalized intrinsic radical cations for polymerization, followed by photooxidation for termination with structural shaping to form PDs. This synthetic approach excludes any external additives, rendering a conversion rate of the precursor exceeding 99%. The prepared PDs, as a single entity, can realize the integration of nanocore luminescence and precursor-transferred luminescence, showing 41.5% of the total absolute luminescence quantum efficiency, which is higher than most reported PD cases. Based on these photoluminescent properties, together with the superior biocompatibility, a unique membrane microenvironmental biodetection could be exemplified. This strategy with programming control of the single precursor can serve as a significant step toward polymer nanomanufacturing with remote control, high-efficiency, precision, and real-time operability.

Light-triggered Modulation of Supramolecular Chirality.

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

Reversible Mechanochromisms via Manipulating Surface Wrinkling.

Mechanochromic structural-colored materials have promising applications in various domains. In this Letter, we report three types of reversible mechanochromisms in simple material systems by harnessing mechano-responsive wrinkling dynamics including (i) brightness mechanochromism (BM), (ii) hue change mechanochromism (HCM), and (iii) viewable angle mechanochromism (VAM). Upon stretching, the BM device exhibits almost a constant hue but reduces light brightness due to the postbuckling mechanics-controlled deformation, while the HCM device can change the hue from blue to red with almost constant intensity because of the linear elastic mechanics-controlled deformation. The VAM device shows a constant hue because of the thin film interference effect. However, the viewable angles decrease with increasing applied strain owing to the light scattering of wrinkles. All of the mechanochromic behaviors exhibit good reversibility and durability. We clearly elucidated the underlying mechanisms for different mechanochromisms and demonstrated their potential applications in smart displays, stretchable strain sensors, and antipeeping/anticounterfeiting devices.

Two-Stage Three-Dimensional Luminescent Sensing Strategy for Precisely Detecting a Wide Range of Water Content in Tetrahydrofuran.

The development of efficient sensors for detecting water content in organic solvents is highly desirable for various cases in the chemical industry. Relevant sensors based on luminescent materials are promising due to their superior sensitivity and visualization. However, reported luminescent probes are either aggregation-caused quenching-type molecules, which present an emission quenching effect in high water content, or aggregation induced emission-type luminogens, which exhibit weak emission in organic solvents. This factor narrows the targeted water-content sensing range. Herein, we developed a series of indoline-based donor-acceptor-donor luminogens involving twist intramolecular charge transfer and an aggregation-induced emission effect, which exhibited a unique "on-off-on" emission behavior in tetrahydrofuran with the continuous increase of water content from 0% to 99%. Simultaneously, the emission wavelength underwent a process of first red-shift and then blue-shift. Three-dimensional working curves based upon the log value of wavelength and emission intensity ratio versus water content in tetrahydrofuran were established with two-stage characteristics, aiming to visually detect a wide range of water content in organic solvents. Such a sensing method offers extra sensitivity, convenience, and accuracy.

Photoexcitation-controlled self-recoverable molecular aggregation for flicker phosphorescence.

Chemical systems with external control capability and self-recoverability are promising since they can avoid additional chemical or energy imposition during the working process. However, it remains challenging to employ such a nonequilibrium method for the engineering of optoelectronic function and for visualization. Here, we report a functional molecule that can undergo intense conformational regulation upon photoexcitation. It enables a dynamical change in hydrophobicity and a follow-up molecular aggregation in aqueous media, accordingly leading to an aggregation-induced phosphorescence (AIP) behavior. This successive performance is self-recoverable, allowing a rapid (second-scale cycle) and long-standing (>103 cycles) flicker ability under rhythmical control of the AIP. Compared with traditional bidirectional manipulations, such monodirectional photocontrol with spontaneous reset profoundly enhances the operability while mostly avoiding possible side reactions and fatigue accumulation. Furthermore, this material can serve as a type of luminescent probe for dynamically strengthening visualization in bioimaging.

Ethyl Phloretate and Ethyl p-Coumarate: Two Phytotoxins from Valsa mali and Their Pathogenic Activities.

Valsa mali, the causal agent of apple Valsa canker, produces several phytotoxic metabolites to promote infection. Bioassay and 1H nuclear magnetic resonance (NMR)-guided isolation from the culture filtrate of V. mali strain 03-8 led to the identification of seven compounds including three unreported ones, ethyl phloretate (1), ethyl p-coumarate (2), and 1-p-hydroxybenzoyl glycerol (3). Compounds 1 and 2 produced significant phytotoxicity, with average lesion areas of 6.22 and 3.74 mm2, along with 2.96 and 3.47 mm2 at 1 mg/ml on mature and tissue-cultured apple leaves, respectively, whereas compound 3 did not cause any symptoms on host plants. The necrotic lesion area of compounds 1 and 2 on tobacco leaves was 52.65 and 48.28 mm2, respectively, compared with the negative control (0.46 mm2) at 1 mg/ml. At the same concentration, compounds 1 and 2 showed no significant influence on the germination rate of lettuce seeds while significantly decreasing the root length of lettuce seedlings to 6.74 and 4.67 mm, respectively, compared with that treated with sterile distilled water (22.01 mm). The discovery indicated that compounds 1 and 2 could be considered as non-host-specific toxins. Furthermore, compounds 1 and 2 could cause cell shrinkage, organelle damage, plasmolysis, and eventually ruptured protoplasmic membranes with cell death for their phytotoxicity in the host plants under optical microscopy and transmission electron microscopy. The results shed light on the mechanism for toxins 1 and 2 in V. mali-infected plants at the macroscopic and cellular levels.

A New Microporous Lanthanide Metal-Organic Framework with a Wide Range of pH Linear Response.

Lanthanide metal-organic frameworks (Ln-MOFs) have attracted extensive attention because of their structural adjustability and wide optical function applications. However, MOFs with a wide linear pH response and stable framework structures in acidic or alkaline solutions are rare to date. Here, we used 4,4',4″-s-triazine-2,4,6-triyltribenzoate (H3TATB) as an organic ligand, coordinated with lanthanide ions (Eu3+/Tb3+), and synthesized a new metal-organic framework material. The material has a porous three-dimensional square framework structure and emits bright red or green fluorescence under 365 nm UV light. The carboxyl group of the ligand is prone to protonation in an acidic environment, and negatively charged OH- and ligand (TATB3-) have a competitive effect in an alkaline environment, which could affect the coordination ability of ligand. The luminescence degree of the framework decreases with the increase in the degree of acid and base. In particular, such fluorescence changes have a wide linear response (pH = 0-14), which can be used as a potential fluorescence sensing material for pH detection.

Recommended risk screening values for Cd in high geological background area of Guangxi, China.

Because of unusually high cadmium concentrations in the soil, the risk screening values of soil Cd in the existing standard is not applicable to the Cd high geological background areas. The aim of our study is to explore recommended risk screening values applicable for Cd high geological background areas of Guangxi, China, to help locals with land management and guarantee the quality and safety of crops as well as providing the theoretical basis for guiding the production safety. A total of 903 pairs of rice samples and root soil samples were collected. The Cd concentration of soil-rice samples and soil pH were determined. The scatter diagram method was used to gradually increase the screening values, and the value with the most samples in the correct interval was counted as the recommended risk screening value. The soil Cd concentrations ranged from 0.06 to 7.08 mg·kg-1 and the rice Cd ranged from 0.002 to 1.488 mg·kg-1; 64.89% of soil samples exceed the RSVs and 27.8% of rice samples exceed the allowable limit of Cd. The recommended risk screening values of Cd in study area were 0.5, 0.7, 1.5, and 2.4 mg·kg-1 for soil with pH ≤ 5.5, 5.5 < pH ≤ 6.5, 6.5 < pH ≤ 7.5, and pH > 7.5, respectively. Compared with the standard screening value, the accuracy of using the recommended screening value as the reference value to judge whether the Cd concentration in rice exceeds the standard was increased by 12%, 20%, 21%, and 47%, respectively. The recommended screening value can be used as the standard value to better indicate the soil environmental quality in the study area.

Fiber-spinning Asymmetric Assembly for Janus-structured Bifunctional Nanofiber Films towards All-Weather Smart Textile.

Given health threat by global warming and increased energy consumption in regulating body temperature, it is an urgent need to construct smart temperature-regulating materials. Herein, a novel fiber-spinning asymmetric chemical assembly (FACA) method is proposed to construct nanofiber materials with asymmetric photothermal properties. The silver nanowires (AgNWs) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with opposite thermal radiation are assembled on reduced graphene oxide (rGO) film, imparting AgNW/rGO/PVDF-HFP film with Janus structure that can realize the AgNWs side consistently keeps temperature of ca. 11 °C lower than the side of PVDF-HFP nanofiber regardless of the irradiation directions under 1 sun, suggesting the adjustable photothermal regulation. Such photothermally selective hybrid nanofiber film provides great potential as fabrics to achieve all-weather smart clothes, promoting controllable and comprehensive utilization of solar energy.

Fibrous Nanoreactors from Microfluidic Blow Spinning for Mass Production of Highly Stable Ligand-Free Perovskite Quantum Dots.

Nano-/micro-reactors have emerged as a powerful platform for chemical synthesis. Here, we develop fiber-spinning chemistry (FSC) based on a microfluidic blow spinning (MBS) technique, allowing the availability of nanoreactors for chemical synthesis with scale-up capacities. Proof-of-concept experiments focus on the utilization of MBS-derived fibrous nanoreactors for large-scale production of ligand-free perovskite quantum dots (PQDs) in one step. Typically, methylammonium lead halide (MAPbX3 , X=Cl, Br, and I) PQDs in situ synthesized at large scale inside polyacrylonitrile (PAN) nanofiber films (size 120 cm ×30 cm per hour), exhibit high photoluminescence (PL) quantum yield (QY) of 71 %, tunable emissive peaks (448-600 nm), and superb PL stability. The PQDs/polymer nanofiber films are potentially useful for CO2 conversion, wide-color-gamut displays and light-emitting diode (LED) devices. These findings may guide the development of nano-/micro-reactor technology for scale-up production of nanomaterials with various potential applications.

Photoexcitation-Based Supramolecular Access to Full-Scale Phase-Diagram Structures through in situ Phase-Volume Ratio Phototuning.

Controlling phase separation and transition plays a core role in establishing and maintaining the function of diverse self-assembled systems. However, it remains challenging to achieve wide-range continuous phase transition for dynamically producing a variety of assembled structures. Here, we developed a far-from-equilibrium system, upon the integration of photoexcitation-induced aggregation molecules and block copolymers, to establish an in situ phase-volume ratio photocontrol strategy. Thus, full-scale phase-diagram structures, from lamellar structure to gyroidal, cylindrical, and finally to a spherical one, can be accessed under different irradiation periods. Moreover, the phase transition was accompanied by considerable aggregation-induced phosphorescence and hydrophilicity/hydrophobicity change for building a functional surface. This strategy allows for a conceptual advance of accessing a wide range of distinct self-assembled structures and functions in real time.

Rigid Polymer Network-Based Autonomous Photoswitches Working in the Solid State Encoded by Room-Temperature Phosphorescence.

Autonomous molecular switches with self-recoverability are of great theoretical and experimental interest since they can avoid additional chemical or energy imposition during the working process. Due to the high energy barrier, however, the solid state is generally unfavorable for materials to exhibit the autonomous switch behavior. To promote the practical usage of the autonomous molecular switch, herein, we propose a prototype of an autonomous photoswitch that can work in the solid state based on a rigid polymer network. A hexacarboxylic sodium-modified hexathiobenzene compound was employed as a photoexcitation-driven unit, which can undergo molecular aggregation upon irradiation because of the distinct conformational difference between the ground state and the photoexcited state. Then, we selected a relatively rigid polymer named poly(dimethyldiallylammonium)chloride (PDDA) to complex with the hexacarboxylic sodium-modified hexathiobenzene through electrostatic coupling. Through optimization, the photoexcitation-controlled molecular aggregation and its self-recovery can work well in the solid matrix of PDDA under rhythmical photoirradiation. This process can be easily encoded by a self-recoverable room-temperature phosphorescence, featuring an excellent performance of the autonomous switch.

Synthesis, Self-assembly, and Fluorescence Application of Bottlebrush Polyfluorene-g-Polycaprolactone with Conjugated Backbone and Crystalline Brushes.

A series of bottlebrush copolymers with conjugated backbone and crystalline branch chains, polyfluorene-g-polycaprolactone (PF-g-PCL), are synthesized by combining Suzuki cross-coupling polymerization and cationic ring-opening polymerization. The PF-g-PCLs are prepared to self-assembled in solution and thin film. Due to the J-type aggregation of the polyfluorene main chains, the self-assembly spherical micelles have been observed. Meanwhile, in film, they exhibited self-assembly ringed spherulites because of the PF microregions in the bottlebrush copolymer. As a result of the interruption of PCL side chains, the aggregation tendency of PF main chains is weakened. And both the polymer solution and solid can overcome the aggregation-caused quenching to provide more pronounced fluorescence. Especially, owing to the good processability of the PF-g-PCL, as a fluorescent ink for different substrates, they can easily be prepared as high-brightness fluorescent films that are invisible under ambient light.

Rapid Fabrication of Patterned Gels via Microchannel-Conformal Frontal Polymerization.

From the perspective of both fundamental and applied science, it is extremely advisable to develop a facile and feasible strategy for fabricating gels with defined structures. Herein, the authors report the rapid synthesis of patterned gels by conducting frontal polymerization (FP) at millimeter-scale (2 mm), where a series of microchannels, including linear-, parallel-, divergent-, snakelike-, circular- and concentric circular channels, were used. They have investigated the effect of various factors (monomer mass ratio, channel size, initiator concentration, and solvent content) on FP at millimeter-scale, along with the propagating rule of the front during FP in these microchannels. In addition, we developed a new microfluidic-assisted FP (MFP) strategy by combining the FP and microfluidic technique. Interestingly, the MFP can realize the production of hollow-structured gel in a rapid and continuous fashion, which have never been reported. Our work not only offers an effective pathway towards patterned gels by the microchannel-conformal FP, but also gives new insight into the continuous production of hollow-structured materials. Such a method will be beneficial for fabricating vessel and scaffold materials in a flexible, easy-to-perform, time and energy saving way.