Finely manipulating room temperature phosphorescence by dynamic lanthanide coordination toward multi-level information security.

Room temperature phosphorescence materials have garnered significant attention due to their unique optical properties and promising applications. However, it remains a great challenge to finely manipulate phosphorescent properties to achieve desirable phosphorescent performance on demand. Here, we show a feasible strategy to finely manipulate organic phosphorescent performance by introducing dynamic lanthanide coordination. The organic phosphors of terpyridine phenylboronic acids possessing excellent coordination ability are covalently embedded into a polyvinyl alcohol matrix, leading to ultralong organic room temperature phosphorescence with a lifetime of up to 0.629 s. Notably, such phosphorescent performance, including intensity and lifetime, can be well controlled by varying the lanthanide dopant. Relying on the excellent modulable performance of these lanthanide-manipulated phosphorescence films, multi-level information encryption including attacker-misleading and spatial-time-resolved applications is successfully demonstrated with greatly improved security level. This work opens an avenue for finely manipulating phosphorescent properties to meet versatile uses in optical applications.

Measuring and classifying IP usage scenarios: a continuous neural trees approach.

Understanding user behavior via IP addresses is a crucial measure towards numerous pragmatic IP-based applications, including online content delivery, fraud prevention, marketing intelligence, and others. While profiling IP addresses through methods like IP geolocation and anomaly detection has been thoroughly studied, the function of an IP address-e.g., whether it pertains to a private enterprise network or a home broadband-remains underexplored. In this work, we initiate the first attempt to address the IP usage scenario classification problem. We collect data consisting of IP addresses from four large-scale regions. A novel continuous neural tree-based ensemble model is proposed to learn IP assignment rules and complex feature interactions. We conduct extensive experiments to evaluate our model in terms of classification accuracy and generalizability. Our results demonstrate that the proposed model is capable of efficiently uncovering significant higher-order feature interactions that enhance IP usage scenario classification, while also possessing the ability to generalize from the source region to the target one.

Targeting Compact and Ordered Emitters by Supramolecular Dynamic Interactions for High-performance Organic Ambient Phosphorescence.

Purely organic room-temperature phosphorescence (RTP) materials have received intense attention due to their fascinating optical properties and advanced optoelectronic applications. The promotion of intersystem crossing (ISC) and minimalization of nonradiative dissipation under ambient conditions are key prerequisites for realizing high-performance organic RTP; However, the ISC process is generally inefficient for organic fluorogens and the populated triplet excitons are always too susceptible to be well stabilized by conventional means. Particularly, organizing organic fluorophores into compact and ordered entities by supramolecular dynamic interactions has proven to be a newly-emerged strategy to boost the ISC process greatly and suppress the non-radiative relaxations immensely, facilitating the population and stabilization of triplet excitons to access high-performance organic RTP. Consequently, well-defined organic emitters enable robust RTP emission even in the solution state, thus greatly extending the applications. Here, this review is focused on a timely and brief introduction to recent progress in tailoring ordered high-performance RTP emitters by supramolecular dynamic interactions. Their typical preparation strategies, optoelectronic properties, and applications are thoroughly summarized. In the summary section, key challenges and perspectives of this field are highlighted to suggest potential directions for future study.

Light-Writing and Projecting Multicolor Fluorescent Hydrogels for On-Demand Information Display.

Intelligent rewritable display systems have been long expected to reduce the heavy consumption of single-use or transient devices in the age of Internet-of-Things. However, it remains challenging to construct such systems with integrated functionality of remote control, rapid activation, multicolor and multimode display. Herein, by learning from the unique multilayer arrangement of chromatophores in chameleon skins, a promising kind of rewritable hydrogel multicolor systems is presented that can combine the merits of near-infrared (NIR) light-writing and projecting modes for on-demand information display. Specifically, the systems have typical multilayer layout consisting of poly(dimethylsiloxane) (PDMS)-sealed carbon nanotubes (CNTs) film as photothermal control unit and embedded fluorescent hydrogels as multicolor display unit, in which thermoresponsive hydrogel is constrained within non-responsive hydrogel. Such rational structure design results in the establishment of one promising display mechanism via the cascading "light trigger-heat generation-fluorescence output" process. On this basis, rapid and reversible hand-written display of arbitrary information is achieved within 5 s. Also, sustainable light-projecting display of predesigned multicolor patterns is demonstrated due to the multilayer design that ensures easy patterning of photothermal control or hydrogel display layer. This study brings functional-integrated merits for novel rewritable display systems and open new possibility to construct high-end products for information display/transmission.

A dinoflagellate-inspired mechanochromic film for fast and reversible information encryption and display.

Inspired by dinoflagellates, we developed a flexible film consisting of spiropyran-based soft polyacrylate and Zn(OTf)2. The open-ring form of spiropyran coordinated with Zn(OTf)2 under stretching to produce a visible fluorescent color change from colorless to yellow. The potential of this film was demonstrated for fast and reversible information encryption and decryption.

Bioinspired Adaptive, Elastic, and Conductive Graphene Structured Thin-Films Achieving High-Efficiency Underwater Detection and Vibration Perception.

Underwater exploration has been an attractive topic for understanding the very nature of the lakes and even deep oceans. In recent years, extensive efforts have been devoted to developing functional materials and their integrated devices for underwater information capturing. However, there still remains a great challenge for water depth detection and vibration monitoring in a high-efficient, controllable, and scalable way. Inspired by the lateral line of fish that can sensitively sense the water depth and environmental stimuli, an ultrathin, elastic, and adaptive underwater sensor based on Ecoflex matrix with embedded assembled graphene sheets is fabricated. The graphene structured thin film is endowed with favourable adaptive and morphable features, which can conformally adhere to the structural surface and transform to a bulged state driven by water pressure. Owing to the introduction of the graphene-based layer, the integrated sensing system can actively detect the water depth with a wide range of 0.3-1.8 m. Furthermore, similar to the fish, the mechanical stimuli from land (e.g. knocking, stomping) and water (e.g. wind blowing, raining, fishing) can also be sensitively captured in real time. This graphene structured thin-film system is expected to demonstrate significant potentials in underwater monitoring, communication, and risk avoidance.

Aggregation-Induced Emissive Carbon Dots Gels for Octopus-Inspired Shape/Color Synergistically Adjustable Actuators.

Some living organisms such as the octopus have fantastic abilities to simultaneously swim away and alter body color/morphology for disguise and self-protection, especially when there is a threat perception. However, it is still quite challenging to construct artificial soft actuators with octopus-like synergistic shape/color change and directional locomotion behaviors, but such systems could enhance the functions of soft robotics dramatically. Herein, we proposed to utilize unique hydrophobic carbon dots (CDs) with rotatable surficial groups to construct the aggregation-induced emission (AIE) active glycol CDs polymer gel, which could be further employed to be interfacially bonded to an elastomer to produce anisotropic bilayer soft actuator. When putting the actuator on a water surface, glycol spontaneously diffused out from the gel layer to allow water intake, resulting in a color change from a blue dispersion fluorescence to red AIE and a shape deformation, as well as a large surface tension gradient that can promote its autonomous locomotion. Based on these findings, artificial soft swimming robots with octopus-like synergistic shape/color change and directional swimming motion were demonstrated. This study provides an elegant strategy to develop advanced multi-functional bio-inspired intelligent soft robotics.

Hybrid Pyramid Convolutional Network for Multiscale Face Detection.

Face detection remains a challenging problem due to the high variability of scale and occlusion despite the strong representational power of deep convolutional neural networks and their implicit robustness. To handle hard face detection under extreme circumstances especially tiny faces detection, in this paper, we proposed a multiscale Hybrid Pyramid Convolutional Network (HPCNet), which is a one-stage fully convolutional network. Our HPCNet consists of three newly presented modules: firstly, we designed the Hybrid Dilated Convolution (HDC) module to replace the fully connected layers in VGG16, which enlarges receptive field and reduces its loss of local information; secondly, we constructed the Hybrid Feature Pyramid (HFP) to combine semantic information from higher layers together with details from lower layers; and thirdly, to deal with the problem of occlusion and blurring effectively, we introduced Context Information Extractor (CIE) in HPCNet. In addition, we presented an improved Online Hard Example Mining (OHEM) strategy, which can enhance the average precision of face detection by balancing the number of positive and negative samples. Our method has achieved an accuracy of 0.933, 0.924, and 0.848 on the Easy, Medium, and Hard subset of WIDER FACE, respectively, which surpasses most of the advanced algorithms.

Acid-Activated Motion Switching of DB24C8 between Two Discrete Platinum(II) Metallacycles.

The precise operation of molecular motion for constructing complicated mechanically interlocked molecules has received considerable attention and is still an energetic field of supramolecular chemistry. Herein, we reported the construction of two tris[2]pseudorotaxanes metallacycles with acid-base controllable molecular motion through self-sorting strategy and host-guest interaction. Firstly, two hexagonal Pt(II) metallacycles M1 and M2 decorated with different host-guest recognition sites have been constructed via coordination-driven self-assembly strategy. The binding of metallacycles M1 and M2 with dibenzo-24-crown-8 (DB24C8) to form tris[2]pseudorotaxanes complexes TPRM1 and TPRM2 have been investigated. Furthermore, by taking advantage of the strong binding affinity between the protonated metallacycle M2 and DB24C8, the addition of trifluoroacetic acid (TFA) as a stimulus successfully induces an acid-activated motion switching of DB24C8 between the discrete metallacycles M1 and M2. This research not only affords a highly efficient way to construct stimuli-responsive smart supramolecular systems but also offers prospects for precisely control multicomponent cooperative motion.

Orthogonal Self-Assembly of a Two-Step Fluorescence-Resonance Energy Transfer System with Improved Photosensitization Efficiency and Photooxidation Activity.

During the past few decades, fabrication of multistep fluorescence-resonance energy transfer (FRET) systems has become one of the most attractive topics within supramolecular chemistry, chemical biology, and materials science. However, it is challenging to efficiently prepare multistep FRET systems with precise control of the distances between locations and the numbers of fluorophores. Herein we present the successful fabrication of a two-step FRET system bearing specific numbers of anthracene, coumarin, and BODIPY moieties at precise distances and locations through an efficient and controllable orthogonal self-assembly approach based on metal-ligand coordination and host-guest interactions. Notably, the photosensitization efficiency and photooxidation activity of the two-step FRET system gradually increased with the number of energy transfer steps. For example, the two-step FRET system exhibited 1.5-fold higher 1O2 generation efficiency and 1.2-fold higher photooxidation activity than that of its corresponding one-step FRET system. This research not only provides the first successful example of the efficient preparation of multistep FRET systems through orthogonal self-assembly involving coordination and host-guest interactions but also pushes multistep FRET systems toward the application of photosensitized oxidation of a sulfur mustard simulant.

Visible-Light-Driven Rotation of Molecular Motors in Discrete Supramolecular Metallacycles.

The organization of molecular motors in supramolecular assemblies to allow the amplification and transmission of motion and collective action is an important step toward future responsive systems. Metal-coordination-driven directional self-assembly into supramolecular metallacycles provides a powerful strategy to position several motor units in larger structures with well-defined geometries. Herein, we present a pyridyl-modified molecular motor ligand (MPY) which upon coordination with geometrically distinct di-Pt(II) acceptors assembles into discrete metallacycles of different sizes and shapes. This coordination leads to a red-shift of the absorption bands of molecular motors, making these motorized metallacycles responsive to visible light. Photochemical and thermal isomerization experiments demonstrated that the light-driven rotation of the motors in the metallacycles is similar to that in free MPY in solution. CD studies show that the helicity inversions associated with each isomerization step in the rotary cycle are preserved. To explore collective motion, the trimeric motor-containing metallacycle was aggregated with heparin through multiple electrostatic interactions, to construct a multi-component hierarchical system. SEM, TEM, and DLS measurements revealed that the photo- and thermal-responsive molecular motor units enabled selective manipulation of the secondary supramolecular aggregation process without dissociating the primary metallacycle structures. These visible-light-responsive metallacycles, with intrinsic multiple rotary motors, offer prospects for cooperative operations, dynamic hierarchical self-assembled systems, and adaptive materials.

Metallo-Helicoid with Double Rims: Polymerization Followed by Folding by Intramolecular Coordination.

In this study, we established a feasible strategy to construct a new type of metallo-polymer with helicoidal structure through the combination of covalent polymerization and intramolecular coordination-driven self-assembly. In the design, a tetratopic monomer (M) was prepared with two terminal alkynes in the outer rim for polymerization, and two terpyridines (TPYs) in the inner rim for subsequent folding by selective intramolecular coordination. Then, the linear covalent polymer (P) was synthesized by polymerization of M via Glaser-Hay homocoupling reaction. Finally, intramolecular coordination interactions between TPYs and Zn(II) folded the backbone of P into a right- or left-handed metallo-helicoid (H) with double rims. Owing to multiple positive charges on the inner rim of helicoid, double-stranded DNA molecules (dsDNA) could interact with H through electrostatic interactions. Remarkably, dsDNA allowed exclusive formation of H with right handedness by means of chiral induction.

Aggregation-Induced Emissive and Circularly Polarized Homogeneous Sulfono-γ-AApeptide Foldamers.

Through our continuous effort in developing a new class of foldamers, we have both designed and synthesized homogenous sulfono-γ-AApeptides using tetraphenylethylene (TPE) moieties attached to the backbone as luminogenic sidechains. Based on previous crystal structures, we have found that these foldamers adopted a left-handed 414-helix. Due to the constraint of the helical scaffold, the rotation of the TPE moieties were restricted, leading to fluorescent emissive properties with high quantum yields not only at the aggregate state but also in solution. Investigation of the relationship between the structure and fluorescence behavior reveals that emission was induced by the combined effect of the aggregation-induced emission (AIE) and the rotated restriction from the backbone. Furthermore, as the packing mode of the luminogens could be precisely adjusted by the helical backbone, these foldamers were found to be circularly polarizable with relatively large luminescence dissymmetry factor (g lum). Interestingly, possessing cationic amphipathic structures similar to that of host-defense peptides (HDPs), these sulfono-γ-AApeptides were able to inhibit the growth of Gram-positive bacteria methicillin-resistant S. aureus (MRSA) through membrane interactions.

Rotaxane-Branched Dendrimers with Enhanced Photosensitization.

During the past few decades, fabrication of functional rotaxane-branched dendrimers has become one of the most attractive yet challenging topics within supramolecular chemistry and materials science. Herein, we present the successful fabrication of a family of new rotaxane-branched dendrimers containing up to 21 platinum atoms and 42 photosensitizer moieties through an efficient and controllable divergent approach. Notably, the photosensitization efficiencies of these rotaxane-branched dendrimers gradually increased with the increase of dendrimer generation. For example, third-generation rotaxane-branched dendrimer PG3 revealed 13.3-fold higher 1O2 generation efficiency than its corresponding monomer AN. The enhanced 1O2 generation efficiency was attributed to the enhancement of intersystem crossing (ISC) through the simple and efficient incorporation of multiple heavy atoms and photosensitizer moieties on the axles and wheels of the rotaxane units, respectively, which has been validated by UV-visible and fluorescence techniques, time-dependent density functional theory calculations, photolysis model reactions, and apparent activation energy calculations. Therefore, we develop a new promising platform of rotaxane-branched dendrimers for the preparation of effective photosensitizers.

Giant Concentric Metallosupramolecule with Aggregation-Induced Phosphorescent Emission.

Fluorescent metallosupramolecules have received considerable attention due to their precisely controlled dimensions as well as the tunable photophysical and photochemical properties. However, phosphorescent analogues are still rare and limited to small structures with low-temperature phosphorescence. Herein, we report the self-assembly and photophysical studies of a giant, discrete metallosupramolecular concentric hexagon functionalized with six alkynylplatinum(II) bzimpy moieties. With a size larger than 10 nm and molecular weight higher than 26 000 Da, the assembled terpyridine-based supramolecule displayed phosphorescent emission at room temperature. Moreover, the supramolecule exhibited enhanced aggregation-induced phosphorescent emission compared to the ligand by tuning the aggregation states through intermolecular interactions and significant enhancement of emission to CO2 gas.

Efficient self-assembly of heterometallic triangular necklace with strong antibacterial activity.

Sophisticated mechanically interlocked molecules (MIMs) with interesting structures, properties and applications have attracted great interest in the field of supramolecular chemistry. We herein report a highly efficient self-assembly of heterometallic triangular necklace 1 containing Cu and Pt metals with strong antibacterial activity. Single-crystal X-ray analysis shows that the finely arranged triangular necklace 1 has two racemic enantiomers in its solid state with intriguing packing motif. The superior antibacterial activity of necklace 1 against both standard and clinically drug-resistant pathogens implies that the presence of Cu(I) center and platinum(II) significantly enhance the bacterium-binding/damaging activity, which is mainly attributed to the highly positively charged nature, the possible synergistic effect of heterometals in the necklace, and the improved stability in culture media. This work clearly discloses the structure-property relationships that the existence of two different metal centers not only facilitates successful construction of heterometallic triangular necklace but also endows it with superior nuclease properties and antibacterial activities.

Daisy Chain Dendrimers: Integrated Mechanically Interlocked Molecules with Stimuli-Induced Dimension Modulation Feature.

The precise construction of the high-order mechanically interlocked molecules (MIMs) with well-defined topological arrangements of multiple mechanically interlocked units has been a great challenge. Herein, we present the first successful preparation of a new family of daisy chain dendrimers, in which the individual [c2]daisy chain rotaxane units serve as the branches of dendrimer skeleton. In particular, the third-generation daisy chain dendrimer with 21 [c2]daisy chain rotaxane moieties was realized, which might be among the most complicated discrete high-order MIMs comprised of multiple [c2]daisy chain rotaxane units. Interestingly, such unique topological arrangements of multiple stimuli-responsive [c2]daisy chain rotaxanes endowed the resultant daisy chain dendrimers controllable and reversible nanoscale dimension modulation through the collective and amplified extension/contraction of each [c2]daisy chain rotaxane branch upon the addition of acetate anions or DMSO molecules as external stimulus. Furthermore, on the basis of such an intriguing size switching feature of daisy chain dendrimers, dynamic composite polymer films were constructed through the incorporation of daisy chain dendrimers into polymer films, which could undergo fast, reversible, and controllable shape transformations when DMSO molecules were employed as stimulus. The successful merging of [c2]daisy chain rotaxanes and dendrimers described herein provides not only a brand-new type of high-order mechanically interlocked systems with well-defined topological arrangements of [c2]daisy chain rotaxanes, but also a successful and practical approach toward the construction of supramolecular dynamic materials.

Construction of Supramolecular Liquid-Crystalline Metallacycles for Holographic Storage of Colored Images.

Design and construction of new functionalized supramolecular coordination complexes (SCCs) via coordination-driven self-assembly strategy is highly important in supramolecular chemistry and materials science. Herein, we present a family of well-defined metallacycles decorated with mesogenic forklike dendrons through the strategy of coordination-driven self-assembly. Due to the existence of mesogenic forklike dendrons, the obtained metallacycles displayed the smectic A liquid crystal phase at room temperature while their precursors exhibited the rectangular columnar liquid crystal phase. Interestingly, by taking advantage of the electrostatic interactions between the positively charged metallacycle and the negatively charged heparin, the doping of heparin induced a significant change of the liquid-crystalline behaviors of metallacycles. More importantly, the prepared liquid-crystalline metallacycles could be further applied for holographic storage of colored images. Notably, the rhomboidal metallacycle and hexagonal metallacycle gave rise to different holographic performances although they featured a similar liquid crystal phase behavior. Therefore, this research not only provides the first successful example of supramolecular liquid-crystalline metallacycles for holographic storage of colored images but also opens a new door for supramolecular liquid-crystalline metallacycles toward advanced optical applications.

Fatigue Limit of Custom 465 with Surface Strengthening Treatment.

In order to study the effect of nitriding or shot peening on the surface modification and fatigue properties of martensitic stainless-steel Custom 465, the residual stress and micro-hardness of the strengthened layer are determined by X-ray and micro-hardness tester, respectively. The up-and-down method is used to measure the rotational bending fatigue strength at 1 × 107 cycles, and the fatigue fracture characteristic is observed by scanning electron microscopy. The relationship between surface residual stress and internal fatigue limit of surface strengthening treatment is discussed. Results show that nitriding or shot peening surface strengthening layer forms a certain depth of compressive residual stress, where in the surface compressive residual stress of the nitrided specimens is greater than the shot peened specimens. The micro-hardness of the nitrided or shot peened surface strengthening layer is significantly improved, where in the surface micro-hardness of nitriding specimens are higher than shot peening specimens. The nitriding or shot peening surface strengthening can significantly improve the fatigue limit of Custom 465, wherein the fatigue limits of nitrided and shot peened surface strengthened specimens are 50.09% and 50.66% higher than that of the un-surface strengthened specimens, respectively. That is, the effect of the two strengthening methods on fatigue limit is not very different. The fracture characteristics show that the fatigue crack of the un-surface strengthened specimens originates from the surface, while the fatigue crack of surface strengthened specimens originates from the subsurface layer under the strengthened layer. The relationship between the internal fatigue limit and the surface residual stress of the surface strengthened specimen can be used as a method for predicting the fatigue limit of the surface strengthened specimens.

Hierarchical self-assembly of discrete bis-[2]pseudorotaxane metallacycle with bis-pillar[5]arene via host-guest interactions and their redox-responsive behaviors.

A discrete rhomboidal metallacycle R functionalized with bis-[2]pseudorotaxane of [Cu(phenanthroline)2]+ derivatives was successfully synthesized via coordination-driven self-assembly. Furthermore, the host-guest complexation of such a bis-[2]pseudorotaxane metallacycle with a bis-pillar[5]arene (bisP5) allowed for the formation of a new family of cross-linked supramolecular polymers R⊃(bisP5)2, which displayed interesting redox-responsive properties. By taking advantage of the substantial structural differences between the coordination geometries of [Cu(phenanthroline)2]+ and [Cu(phenanthroline)2]2+, the weight-average diffusion coefficients D of the supramolecular polymer were adjusted through changing the redox state of the Cu(i)/Cu(ii) complexes.