Smart gas sensor arrays powered by artificial intelligence

Mobile robots behaving as humans should possess multifunctional flexible sensing systems including vision,hearing,touch,smell,and taste.A gas sensor array(GSA),also known as electronic nose,is a possible solution for a robotic olfactory system that can detect and discriminate a wide variety of gas molecules.Artificial intelligence(AI)applied to an electronic nose involves a diverse set of machine learning algorithms which can generate a smell print by analyzing the signal pattern from the GSA.A combination of GSA and AI algorithms can empower intelligent robots with great capabilities in many areas such as environmental monitoring,gas leakage detection,food and beverage production and storage,and especially disease diagnosis through detection of different types and concentrations of target gases with the advantages of portability,low-powerconsumption and ease-of-operation.It is exciting to envisage robots equipped with a"nose"acting as family doctor who will guard every family member's health and keep their home safe.In this review,we give a summary of the state-of the-art research progress in the fabrication techniques for GSAs and typical algorithms employed in artificial olfactory systems,exploring their potential applications in disease diagnosis,environmental monitoring,and explosive detection.We also discuss the key limitations of gas sensor units and their possible solutions.Finally,we present the outlook of GSAs over the horizon of smart homes and cities.

Large-scale, adhesive-free and omnidirectional 3D nanocone anti-reflection films for high performance photovoltaics

An effective and low-cost front-side anti-reflection(AR) technique has long been sought to enhance the performance of highly efficient photovoltaic devices due to its capability of maximizing the light absorption in photovoltaic devices. In order to achieve high throughput fabrication of nanostructured flexible and anti-reflection films, large-scale, nano-engineered wafer molds were fabricated in this work. Additionally, to gain in-depth understanding of the optical and electrical performance enhancement with AR films on polycrystalline Si solar cells, both theoretical and experimental studies were performed. Intriguingly,the nanocone structures demonstrated an efficient light trapping effect which reduced the surface reflection of a solar cell by17.7% and therefore enhanced the overall electric output power of photovoltaic devices by 6% at normal light incidence. Notably, the output power improvement is even more significant at a larger light incident angle which is practically meaningful for daily operation of solar panels. The application of the developed AR films is not only limited to crystalline Si solar cells explored here, but also compatible with any types of photovoltaic technology for performance enhancement.

Recent progress of efficient flexible solar cells based on nanostructures

Flexible solar cells are important photovoltaics(PV)technologies due to the reduced processing temperature,less material consumption and mechanical flexibility,thus they have promising applications for portable devices and building-integrated applications.However,the efficient harvesting of photons is the core hindrance towards efficient,flexible PV.Light management by nanostructures and nanomaterials has opened new pathways for sufficient solar energy harvesting.Nanostructures on top surfaces provide an efficient pathway for the propagation of light.Aside from suppressing incident light reflection,micro-structured back-reflectors reduce transmission via multiple reflections.Nanostructures themselves can be the absorber layer.Photovoltaics based on high-crystallinity nanostructured light absorbers demonstrate enhanced power conversion efficiency(PCE)and excellent mechanical flexibility.To acquire a deep understanding of the impacts of nanostructures,herein,a concise overview of the recent development in the design and application of nanostructures and nanomaterials for photovoltaics is summarized.

Clustering Algorithms to Analyze Molecular Dynamics Simulation Trajectories for Complex Chemical and Biological Systems

Molecular dynamics （MD） simulation has become a powerful tool to investigate the structure- function relationship of proteins and other biological macromolecules at atomic resolution and biologically relevant timescales. MD simulations often produce massive datasets con- taining millions of snapshots describing proteins in motion. Therefore, clustering algorithms have been in high demand to be developed and applied to classify these MD snapshots and gain biological insights. There mainly exist two categories of clustering algorithms that aim to group protein conformations into clusters based on the similarity of their shape （geometric clustering） and kinetics （kinetic clustering）. In this paper, we review a series of frequently used clustering algorithms applied in MD simulations, including divisive algorithms, ag- glomerative algorithms （single-linkage, complete-linkage, average-linkage, centroid-linkage and ward-linkage）, center-based algorithms （K-Means, K-Medoids, K-Centers, and APM）, density-based algorithms （neighbor-based, DBSCAN, density-peaks, and Robust-DB）, and spectral-based algorithms （PCCA and PCCA＋）. In particular, differences between geomet- ric and kinetic clustering metrics will be discussed along with the performances of diflhrent clustering algorithms. We note that there does not exist a one-size-fits-all algorithm in the classification of MD datasets. For a specific application, the right choice of clustering algo- rithm should be based on the purpose of clustering, and the intrinsic properties of the MD conformational ensembles. Therefore, a main focus of our review is to describe the merits and limitations of each clustering algorithm. We expect that this review would be helpful to guide researchers to choose appropriate clustering algorithms for their own MD datasets.

“On Water”Effect for Green Click Reaction:Spontaneous Polymerization of Activated Alkyne with“Inert”Aromatic Amine in Aqueous Media

Organic reactions in water have attracted great attention due to their advantages such as unique reaction performance and environmental friendliness.Organic reactions as well as polymerizations in aqueous media have been extensively investigated,and so far,there has been a massive amount of reporting about polymerizations in water.However,reports about click polymerization in water have been rare.Herein,click polymerization of activated alkyne and aromatic amine in aqueous media is developed.The“on water”effect facilitates polymerization in aqueous media better than in organic solvents,and its mechanism is deciphered through experimental data and theoretical calculations.Water participates in the reaction and reduces the energy barrier to some extent.Besides,polymerization makes it possible for aromatic amine with low reactivity to be linked.By using this strategy,polymers with high molecular weights can be obtained in high yields(up to 95.4%).They show good thermal stability and high refractivity.They can be photodegraded.The polymers with tetraphenylethylene moieties show aggregation-induced emission and can be used as materials for generating photopatterns and visualizing agents for specific staining of lysosome in living cells.

Aggregation-induced emission biomaterials for anti-pathogen medical applications:detecting,imaging and killing

Microbial pathogens,including bacteria,fungi and viruses,greatly threaten the global public health.For pathogen infections,early diagnosis and precise treatment are essential to cut the mortality rate.The emergence of aggregation‐induced emission(AIE)biomaterials provides an effective and promising tool for the theranostics of pathogen infections.In this review,the recent advances about AIE biomaterials for anti-pathogen theranostics are summarized.With the excellent sensitivity and photostability,AIE biomaterials have been widely applied for precise diagnosis of pathogens.Besides,different types of anti-pathogen methods based on AIE biomaterials will be presented in detail,including chemotherapy and phototherapy.Finally,the existing deficiencies and future development of AIE biomaterials for anti-pathogen applications will be discussed.

Recent Progress in AIE-active Polymers

The demand for highly efficient solid-state luminophores is continuously growing due to their potential applications in optoelectrical devices, chemosensors, and biological applications. The discovery of luminogens with aggregation-induced emission(AIE)by Tang et al. in 2001 provides a good reponse to this demand. Among the exploited AIE luminogens, AIE-active polymers possess many advantages such as simple synthesis, convenient structrue modifications, and good processability, which offer an extensive platform for scientists and engineers. Herein, the design principles and latest synthetic advancement of AIE-active polymers are summarized, including click polymerization and multicomponent polymerization. Non-conjugated heteroatom-rich polymers were in situ generated and demonstated non-conventional clusteroluminoscence. Advanced applications including fluorescent sensors, stimuli-responsive materials,biological applications, circularly polarized luminescence, and electroluminescence are then introduced in detail. AIE-active polymers display the signal-amplification effect for sensitive and selective response to chemo/bioanalytes or stimuli and enhanced photosensitization effect for cancer theranostics. Retrospecting the expansion of this field can further strengthen our belief that AIE-active polymers are promising for conceptual innovation and technological breakthroughs in the near future.

Electronic effect on the optical properties and sensing ability of AIEgens with ESIPT process based on salicylaldehyde azine

Two novel AIE-active salicylaldehyde azine(SAA) derivatives with a typical excited-state intramolecular proton transfer(ESIPT) process are prepared by introducing electron-withdrawing and donating groups at para-position of phenolic hydroxyl group(CN-SAA and TPA-SAA). The effect of the proton activity in SAA framework on their optical behaviors is investigated spectroscopically. The results from NMR and solvation measurements show that the proton of phenolic hydroxyl group has higher activity when there are electron-withdrawing groups, and the absorption and fluorescence spectra in buffers with different pH also provide the same results. After inviting F. as a nucleophilic probe, this proton activity difference in CN-SAA and TPA-SAA becomes more obvious. The potential application of both molecules is investigated. TPA-SAA exhibits good quantitative sensing ability towards F. with a fluorescence "turn-on" mode, whereas the aggregates of TPA-SAA can selectively and sensitively detect Cu2+ in aqueous solution. From these results, a structure-property relationship is established: the occurrence of ESIPT process will become much easier when linking electron-withdrawing groups at the para-position of phenolic hydroxyl group(e.g., CN-SAA),and it is better to introduce electron-donating groups to enhance the sensing ability towards ions(e.g., TPA-SAA). This work will provide guidance for further design and preparation of AIE-active luminogens with ESIPT process for sensing applications.

A Simple Approach to Bioconjugation at Diverse Levels: Metal-Free Click Reactions of Activated Alkynes with Native Groups of Biotargets without Prefunctionalization

Te efcient bioconjugation of functional groups/molecules to targeted matrix and bio-related species drives the great development of material science and biomedicine,while the dilemma of metal catalysis,uneasy premodifcation,and limited reaction efciency in traditional bioconjugation has restricted the booming development to some extent.Here,we provide a strategy for metal-free click bioconjugation at diverse levels based on activated alkynes.As a proof-of-concept,the abundant native groups including amine,thiol,and hydroxyl groups can directly react with activated alkynes without any modifcation in the absence of metal catalysis.Trough this strategy,high-efcient modifcation and potential functionalization can be achieved for natural polysaccharide,biocompatible polyethylene glycol(PEG),synthetic polymers,cell penetrating peptide,protein,fast whole-cell mapping,and even quick diferentiation and staining of Gram-positive bacteria,etc.Terefore,current metal-free click bioconjugation strategy based on activated alkynes is promising for the development of quick fuorescence labeling and functional modifcation of many targets and can be widely applied towards the fabrication of complex biomaterials and future in vivo labeling and detection.

Optimal extent of fluorination enabling strong temperature-dependent aggregation, favorable blend morphology and high-efficiency polymer solar cells

Temperature-dependent aggregation is a key property for some donor polymers to realize favorable bulk-heterojunction(BHJ)morphologies and high-efficiency(>10%) polymer solar cells.Previous studies find that an important structural feature that enables such temperature-dependent aggregation property is the 2nd position branched alkyl chains sitting between two thiophene units.In this report,we demonstrate that an optimal extent of fluorination on the polymer backbone is a second essential structural feature that enables the strong temperature-dependent aggregation property.We compare the properties of three structurally similar polymers with 0,2 or 4 fluorine substitutions in each repeating unit through an in-depth morphological study.We show that the non-fluorinated polymer does not aggregate in solution(0.02 mg mL^(-1) in chlorobenzene) at room temperature,which results in poor polymer crystallinity and extremely large polymer domains.On the other hand,the polymer with four fluorine atoms in each repeating unit exhibits an excessively strong tendency to aggregate,which makes it difficult to process and causes a large domain.Only the polymer with two fluorine atoms in each repeating unit exhibits a suitable extent of temperature-dependent aggregation property.As a result,its blend film achieves a favorable morphology and high power conversion efficiency.This provides another key design rationale for developing donor polymers with suitable temperature-dependent aggregation properties and thus high performance.

Vapor phase fabrication of three-dimensional arrayed BiI3 nanosheets for cost-effective solar cells

Multilayered photovoltaic absorbers have triggered widespread attention for their unique structure and properties.However,multilayered materials in the randomly oriented polycrystalline thin-film lead to ineffective carrier transport and collection,which hinders the process of achieving high-performance solar cells.Herein,this issue is tackled by producing the three-dimensional(3D)heterojunction BiI3 nanosheets(NSs)solar cells,which embed vertically aligned monocrystalline BiI3 NSs into spiro-OMeTAD.The preferred orientation of BiI3 NSs and large p-n junction areas of 3D heterojunction structure enable a strong light absorption and effective carrier transport and collection,and thus a power conversion efficiency(PCE)of 1.45%was achieved.Moreover,this PCE is the highest ever reported for BiI3 based solar cells to our best knowledge.Moreover,the nonencapsulated device remained 96%of the initial PCE after 24 h continuous one sun illumination at^70%humidity condition,and 82%of the initial PCE after 1-month storage at^30%humidity condition.

Poly-active centric CoO-CeO/Co-N-C composites as superior oxygen reduction catalysts for Zn-air batteries

Zinc-air battery is one of the most promising next-generation energy conversion and storage systems.Green and low-cost catalysts with high oxygen reduction reaction(ORR)catalytic activity are desired to meet the requirements of Zinc-air batteries.Herein,poly-active centric Co3O4-CeO2/Co-N-C(ketjenblack carbon)catalysts were prepared by a facile method.The Co3O4 and CeO2 nanoparticles are uniformly anchored on the surface of Co and N doped carbon support.The half-wave potential of Co3O4-CeO2/Co-N-C in the rotating disk electrode testing is close to that of Pt/C.The Zn-air battery using Co3O4-CeO2/Co-N-C as the cathode catalyst can provide a high specific capacity of 728 mA h g^-1 at 20 mA cm^-2 and maintain a stable discharge voltage.The remarkable catalytic performance is mainly attributed to the synergistic effect among Co3O4,CeO2 and Co-N-C,the outstanding electrical conductivity and the large surface area.Benefitting from the high catalytic activity,environmental friendliness and the facile synthesis process,Co3O4-CeO2/Co-N-C catalyst lends itself well to a great prospect in the application of metalair batteries.

Aggregate Materials beyond AIEgens

CONSPECTUS:Aggregate materials focus on the materials that are constituted by more than a single entity.It could be dimers,trimers,or multimers formed by the group of same molecules or mixtures formed by different molecules.Although materials have different forms such as liquid,hydrogel,colloidal suspension,and powder,aggregates undisputedly are among the most commonly existing forms,which involve many aspects of human daily life such as the clothes we wear,the drugs we take,the food we eat,and the tools and devices we use.Sciences related to aggregate materials are also rich.From molecules to aggregates,different aspects of science such as crystallography,interfacial science,supramolecular science,and engineering science may be involved.Therefore,research on aggregate materials and related mechanisms that dominate the properties of aggregate materials is significant.

A Simple Approach to Achieve Organic Radicals with Unusual Solid-State Emission and Persistent Stability

Sable organic radicals are promising materials for information storage,molecular magnetism,electronic devices,and biological probes.Many organic radicals have been prepared,but most are non-or weakly emissive and degrade easily upon photoexcitation.It remains challenging to produce stable and efficient luminescent radicals because of the absence of general guidelines for their synthesis.Herein,we present a photoactivation approach to generate a stable luminescent radical from tris(4-chlorophenyl)phosph ine(TCPP)with red emission in the crystal state.The mechanistic study suggests that the molecular symmetry breaking in the crystal causes changes of molecular conformation,redox properties,andmolecular packing that facilitates radical generation and stabilization.This design strategy demonstrates a straightforward approach to develop stable organic luminescent radicals that will open new doors to photoinduced luminescent radical materials.

Mitochondria-targeting NIR fluorescent probe for rapid,highly sensitive and selective visualization of nitroxyl in live cells,tissues and mice

Nitroxyl(HNO)has been reported to possess unique biological and pharmacological performances,and emerged as a novel therapy for congestive heart failure.Recent studies also suggest that HNO may be produced and involved in important metabolisms in mitochondria.However,due to its high reactivity and short life properties,fast,sensitive and selective observation and monitoring of HNO related dynamic changes in mitochondria still remains a great challenge.Herein,we synthesized a mitochondria-targeting near-infrared(NIR)fluorescent probe(DCMHNO)for rapid detection of HNO with remarkably high sensitivity,selectivity and photostability.DCMHNO shows fast response(about 4 min)towards HNO via 2-(diphenylphosphino)benzoyl group through the Staudinger reaction to boost the bright NIR emission(700 nm)with excellent sensitivity(detection limit of 13 nM),high p H stability and very low interference from other species.DCMHNO can selectively locate in mitochondria and visualize exogenous and endogenous HNO in live He La cells with high biocompatibility and photostability.The probe could also monitor the interaction between NO and H2 S that gives rise to the generation of HNO in live He La cells.In addition,DCMHNO was further utilized in ex vivo NIR imaging of HNO in live mouse liver tissues at the depth of about 50μm.In vivo imaging of HNO with high signal-to-noise ratio in live mice was also realized by using DCMHNO.These remarkable imaging performances could render NIR DCMNHNO as a useful tool to reveal HNO related dynamic changes in live samples.

In-situ generation of poly(quinolizine)s via catalyst-free polyannulations of activated diyne and pyridines

The development of new polymerization routes to afford N-heterocyclic polymers is of vital importance and highly desired for various practical applications. Herein, a facile and efficient polyannulation reaction of dual-activated alkyne and pyridines was developed to construct novel N-heterocyclic poly(quinolizine)s. This polymerization can proceed smoothly under catalystfree conditions with 100% atom utilization to furnish poly(quinolizine)s with high molecular weights(up to 34,100) and welldefined structures in acceptable yields. The resulting polymers show good solubility, high thermal stability and strong red emission. Moreover, the prepared poly(quinolizine)s exhibit low cytotoxicity and can selectively label lysosomes in live cells.Considering the remarkable advantages of readily available raw materials, mild polymerization conditions, atom economy, and excellent product performance, this new and efficient polymerization tool will open up enormous opportunities for preparing functional N-heterocyclic polymers.

Stable Quadruple Helical Tetraradicaloid with Thermally Induced Intramolecular Magnetic Switching

We report an air-stable tetraradicaloid based on a rarely explored perylenequinonoid(PQ)core,namely,tetrabenzo-annulated tetracyclopenta[b,e,k,n]perylene(TBCP),which has a quadruple helical structure.As validated by X-ray crystallographic analysis and theoretical calculations,the nonplanar TBCP possesses unique hybrid resonance structures of two open-shell singlet diradicaloids.Remarkably,magnetic measurements reveal that TBCP in powder form shows unusual magnetic hysteresis upon heating followed by cooling,corresponding to interconversion of structure isomers with different magnetic properties.Such electronic properties can be rationalized as the response of structural changes to external thermal stimuli,accompanied by a subtle balance of two types of intramolecular magnetic interactions between four-site spin centers.The results provide a novel organic polyradicaloid as an unprecedented example of a functional material with the potential for intramolecular magnetic switching.

In Situ Generation of N-Heteroaromatic Polymers:Metal-Free Multicomponent Polymerization for Photopatterning,Morphological Imaging,and Cr(Ⅵ)Sensing

Electron-deficient N-heteroaromatic polymers are crucial for the high-tech applications of organicmaterials,especially in the electronic and optoelectronic fields.Thus,the development of new polymerizations to afford adaptable electron-donating-accepting scaffolds in N-heteroaromatic polymers is in high demand.Herein,we have developed metal-free multicomponent polymerizations of diynes,diamines,and glyoxylates successfully for in situ generation of poly(quinoline)s with high molecular weights(Mw up to 16,900)in nearly quantitative yields.By tuning the electron distributions of the polymer backbones,the resulting poly(quinoline)s showed various aggregation-induced behaviors and photoresponsive abilities:The thin films of the poly(quinoline)s could be fabricated readily intowell-resolved photopatterns by photolithography techniques.They could be utilized as fluorescent probes to visualize themorphologies of polymer materials directly;these include spherulites and microphase separation of polymer blends.Their nanoparticles demonstrated sensitive and highly selective fluorescence quenching to hexavalent chromium ion Cr(Ⅵ),thereby providing access for biological imaging of Cr(Ⅵ)in unicellular algae.