Machine Learning for Chemistry:Basics and Applications

The past decade has seen a sharp increase in machine learning(ML)applications in scientific research.This review introduces the basic constituents of ML,including databases,features,and algorithms,and highlights a few important achievements in chemistry that have been aided by ML techniques.The described databases include some of the most popular chemical databases for molecules and materials obtained from either experiments or computational calculations.Important two-dimensional(2D)and three-dimensional(3D)features representing the chemical environment of molecules and solids are briefly introduced.Decision tree and deep learning neural network algorithms are overviewed to emphasize their frameworks and typical application scenarios.Three important fields of ML in chemistry are discussed:(1)retrosynthesis,in which ML predicts the likely routes of organic synthesis;(2)atomic simulations,which utilize the ML potential to accelerate potential energy surface sampling;and(3)heterogeneous catalysis,in which ML assists in various aspects of catalytic design,ranging from synthetic condition optimization to reaction mechanism exploration.Finally,a prospect on future ML applications is provided.

Asymmetric side-chain engineering of organic semiconductor for ultrasensitive gas sensing

Molecular structure of organic semiconductor plays a critical role in determining the performance and functionality of organic electronic devices,by optimizing the electrical,optical and physicochemical properties.Substituted alkyl chains are fundamental units in tailering the solubility and assemblability,among which the asymmetric properties have been reported as key element for controlling the packing motifs and intrinsic charge transport.Here,we expanded the scope of molecular asymmetry dependent sensing features based on a new series of naphthalene diimides(NDI)-based derivatives substituted with a same branching alkyl chain but various linear-shaped alkyl chains(Cn-).A clear molecular stacking change,from head-to-head bilayer to head-to-tail monolayer packing model,is observed based on the features of anisotropic molecular interactions with the change in the chain length.Most importantly,a unique LUMO level shift of 0.17 eV is validated for NDI-PhC4,providing a record sensitivity up to 150%to 0.01 ppb ammonia,due to the desired molecular reactivity and device amplification properties.These results indicate that asymmetric side-chain engineering opens a route for breath healthcare.

Photoresponsive organic field-effect transistors involving photochromic molecules

In recent years,organic field-effect transistors（OFETs） with high performance and novel multifunctionalities have attracted considerable attention.Meanwhile,featured with reversible photoisomerization and the corresponding variation in color,chemical/physical properties,photochromic molecules have been applied in sensors,photo-switches and memories.Incorporation of photochromic molecules to blend in the device functional layers or to modify the interfaces of OFETs is common way to build photo-transistors.In this review,we focus on the recent advantages on the study of photoresponsive transistors involving one of three typical photochromic compounds spiropyran,diarylethene and azobenzene.Three main strategies are demonstrated in detail.Firstly,photochromic molecules are doped in active layers or combined with semiconductor structure thus forming photoreversible active layers.Secondly,the modification of dielectric layer/active layer interface is mainly carried out by bilayer dielectric.Thirdly,the photo-isomerization of self-assembled monolayer（SAM） on the electrode/active layer interface can reversibly modulate the work functions and charge injection barrier,result in bifunctional OFETs.All in all,the combination of photochromic molecules and OFETs is an efficient way for the fabrication of organic photoelectric devices.Photoresponsive transistors consisted of photochromic molecules are potential candidate for real applications in the future.

Living Crystallization-Driven Self-Assembly of Oligo(p-phenylene vinylene)-Containing Block Copolymers:Impact of Branched Structure of Alkyl Side Chain ofπ-Conjugated Segment

The structure of side chains ofπ-conjugated segments is a critical factor determining living crystallization-driven self-assembly(CDSA),a versatile platform to generate fiber-like nanostructures with precise length and composition.Herein,we design and synthesize three block copolymers(BCPs)containing same corona-forming poly(N-isopropyl acrylamide)(PNIPAM)segment,but different core-formingπ-conjugated oligo(p-phenylene vinylene)(OPV)with linear pentyl(l-OPV),racemic 2-methyl butyl(r-OPV)and stereo-regular chiral(S)-2-methyl butyl(c-OPV)side chains,respectively.By using these BCPs of l-OPV-b-PNIPAM_(47),r-OPV-b-PNIPAM_(47)and c-OPV-b-PNIPAM_(47)as model,we aim to get a deep insight into how steric and stereo-regular effect induced by branched alkyl side chains of OPV segment affects the living CDSA.The results showed that l-OPV-b-PNIPAM_(47)exhibits typical characteristics of self-seeding and seeded growth of living CDSA to give uniform fiber-like micelles of controlled length.On the contrary,r-OPV-b-PNIPAM_(47)and c-OPV-b-PNIPAM_(47)with branched racemic and stereo-regular chiral alkyl side chains are more prone to self-nucleation during the micellar elongation to give short and polydisperse fiber-like micelles.The obvious selfnucleation during the micellar elongation of r-OPV-b-PNIPAM_(47)and c-OPV-b-PNIPAM_(47)is due to the increase of steric repulsion with OPV units induced by branched alkyl side chains,not the stereo-irregular effect of racemic alkyl side chains.

1,2,5,6-Naphthalene Diimides:A Class of Promising Building Blocks for Organic Semiconductors

Organic semiconductors have drawn extensive atten-tion due to their optoelectronic properties and wide applications in organic optoelectronics.In comparison with the popular 1,4,5,8-naphthalene diimides(1,4,5,8-NDIs),the angular-shaped 1,2,5,6-NDIs have exhibited tunable photophysical properties,self-as-sembly behaviors and charge transporting properties.Due to these unique features,1,2,5,6-NDIs show great potential for construction of high performance n-func-tional materials.In this review,we highlight the recent advances and future prospects of 1,2,5,6-NDI-basedπ-systems in the field of organic optoelectronics,in-cluding molecular design,synthesis,structure-prop-erty relationships as well as the applications in high performance organic field-effect transistors,organic photovoltaics,perovskite solar cells,and so on.

Advanced charge transfer technology for highly efficient and long-lived TADF-type organic afterglow with near-infrared light-excitable property

Heavy atom effects and n-π*transitions have been frequently reported to enhance room-temperature organic phosphorescence efficiency but lead to shortage of phosphorescence lifetimes.Unlike these reported studies,we conceive the incorporation of advanced charge transfer(CT)technology to boost room-temperature organic afterglow efficiency and simultaneously maintain afterglow lifetimes.Here we design difluoroboronβ-diketonate(BF2bdk)CT compounds with moderate singlet-triplet splitting energy(ΔEST)of around 0.4 e V,and relatively large spin-orbit coupling matrix elements(SOCME(S_(1)-T_(1)),1–10 cm^(-1))to achieve efficient intersystem crossing(ISC)and moderate rates of reverse intersystem crossing(kRISC,1–10 s^(-1)).The advanced CT technology,which includes multiple electron-donating groups and orthogonal donor-acceptor arrangement,have been found to narrowΔESTand enhance both ISC and RISC.Meanwhile,the organic matrices suppress nonradiative decay of BF2bdk’s T1states by their rigid microenvironment.Consequently,thermally activated delayed fluorescence(TADF)-type organic afterglow materials can be achieved with afterglow efficiency up to 83.0%,long lifetimes of 433 ms,excellent processablility,as well as advanced anti-counterfeiting and information encryption.Furthermore,with the aid of up-conversion materials and through radiative energy transfer,TADF-type afterglow materials with aqueous dispersity and near-infrared light-excitable property have been achieved,which paves the way for biomedical applications.

Immobilization of GO_(X) on PEG/fluoresence functionalized nanographene oxide to describe fluctuation of glucose level

Enzyme,produced and worked in all living things,could work as macromolecular biological catalysts in diverse biochemical processes with particular specificity,like glucose oxidase(GOX).The efficient use of enzyme properties has great importance in pharmaceutics and therapeutics.In this work,we could fabricate naive and effective electrochemical biosensors in the determination of glucose levels via utilizing GOX.Graphene oxide,as a water-soluble derivative of graphene,has shown great promise in a variety of biomedical applications including biosensors.Thus,we established a new-type special platform for GOX immobilization to perform its prosperities,in which nanographene oxide(nGO)was employed as an ideal base and poly(ethylene glycol)(PEG)was conjugated on the edge of nGO sheets to enhance its biocompatibility.Additionally,preferable functional dyes(Rhodamine B/fluorescein isothiocyanate)were also introduced to the platform.Enzyme-nanocomposites were then provided by locating GOX on the platform,i.e.,GOX@nGO-PEG-RhB and GOX@nGO-PEG-FITC.The microstructure and composite of platforms and enzyme-nanocomposites were confirmed by diverse characterizations.Finally,on account of corresponding cyclic voltammetric and typical ready-state amperometric curves,it was informed that GOX@nGO-PEG-RhB and GOX@nGO-PEG-FITC could effectively respond to the fluctuation of glucose level as electrochemical biosensor.The present work presents special platforms for the immobilization of enzymes like GOX and provides new-type biosensors in the detection of glucose levels.

Soluble Two-dimensional Supramolecular Organic Frameworks(SOFs):An Emerging Class of 2D Supramolecular Polymers with Internal Longrange Orders

Two-dimensional(2D) materials have been demonstrated to exhibit unique properties originating from its 2D nature. In recent years, the construction of 2D materials has become a topic of great interest. This article summarizes the recent advance of 2D supramolecular organic frameworks(SOFs) which are homogeneously constructed in solution phase through self-assembly of rationally designed building blocks. These 2D SOFs are soluble and still maintain stable network structures in solutions, which exhibit uniqueness not only in structures but also in properties. In this concise review, the SOFs-related background is briefly introduced firstly, followed by outlining the research progress of soluble 2D SOFs from the perspective of monomer design, assembly, and structural characterization.The article ends with a personal outlook on the future development of this new class of supramolecular polymers.

Porous organic polymers: a progress report in China

Porous organic polymers(POPs) are porous materials composed of light elements such as C, H, N, and O. The benign characters,including large surface area, good physical and chemical stability, well-defined chemical composition, wide ranges of monomer selection, and strong designability, have made POPs one of the frontiers in materials research. In this review, we discussed the design and synthesis of various POP materials that mainly led by Chinese scientists, including conjugated microporous polymers(CMPs), porous aromatic frameworks(PAFs), and hypercrosslinked porous polymers(HCPs), as well as crystalline POPs comprised of covalent organic frameworks(COFs) and a special class of COFs with triazine rings, covalent triazine frameworks(CTFs), and supramolecular organic frameworks(SOFs), and sorted out their main applications in adsorption, separation,catalysis, and electrochemistry fields.

Supramolecular systems for bioapplications:recent research progress in China

Supramolecular systems feature dynamic,reversible and stimuli-responsive characteristics,which are not easily achieved by molecular entities.The last decade has witnessed tremendous advances in the investigations of supramolecular systems for various bioapplications,which include drug delivery,anticancer therapy,antibacterial therapy,photodynamic therapy,photothermal therapy,combination therapy,antidotes for residual drugs or toxins,and bioimaging and biosensing.Host-guest chemistry has played a key role in the development of such bioactive supramolecular systems,and natural macrocycles(such as cyclodextrins),synthetic macrocycles(such as calixarenes,cucurbit[n]urils,and pillararenes),and porous framework polymers(such as supramolecular organic frameworks and flexible organic frameworks)have been most successfully used as hosts to build different kinds of host-guest systems for attaining designed biofunctions.The self-assembly of rationally designed amphiphilic molecules,macromolecules and polymers represent another important approach for the construction of supramolecular architectures with advanced biofunctions.In this review,we summarize the important contributions made by Chinese researchers in this field,with emphasis on those reported in the past five years.

Viologen derivatives with extendedπ-conjugation structures:From supra-/molecular building blocks to organic porous materials

Recently,increasing atte ntion has been paid on extending theπ-conjugation structures ofviologens(1,1’-disubstituted-4,4’-bipyridylium salts)by incorporating planar aromatic units into the bipyridinium backbones.Various viologen derivative s with extendedπ-conjugation structures have been synthesized,including the N-termini aromatic substituted viologens,the extendedπ-conjugated viologens(denoted as ECVs)as well as theπ-conjugated oligomeric viologens(denoted as COVs).These compounds typically exhibit interesting properties distinguished from those of an isolated viologen unit,which make them as new class of electron deficient supra-/molecular building blocks in supramolecular chemistry and materials science.In this review,we would like to highlight the recent advances of viologen derivatives with extendedπ-conjugation structures in versatile applications ranging from electrochromic and energy storage materials,the ECV/COV-based supramolecular self-assembly systems including the linear supramolecular polymers and 2D/3D supramolecular organic frameworks(SOFs),to the viologen-based covalent organic frameworks(COFs)/networks.We hope this review will serve as an in-time summary worthy of referring,more importantly,to provide inspiration in the rational design of novel molecules with unexplored properties and functions.

Recent Advances in Molecular Design of Organic Thermoelectric Materials

Organic thermoelectric(OTE)materials have gained widespread attention because of their potential for wearable power generators and solid cooling elements.Nevertheless,the development of state-ofthe-art OTE materials still suffers from limited molecular categories because of the rarity ofmolecular design strategies,which limits further development of this emerging field.Recently,many efforts have been devoted to developing molecular design concepts for high performance OTE materials.

Toward a Two-Dimensional Supramolecular Organic Framework with High Degree of Internal Order via Amphiphilic Modification

Solution-phase self-assembly of two-dimensional(2D)networks with a high degree of internal order and long-range periodicity is a great challenge.Herein,we report a rational design to improve 2D self-assembly in water through amphiphilic modification of the building block.An amphiphilic tritopic molecule(1)is designed and synthesized by introducing three hydrophilic oligo(ethylene glycol)moieties and three hydrophobic hexyl chains.The assembly of 1 and cucurbit[8]uril(CB[8])leads to the formation of a Janus 2D supramolecular organic framework(SOF),which further creates unique bilayer supramolecular networks and exhibits an unprecedentedly high degree of internal order and long-range periodicity.In contrast,the assembly of a nonamphiphilic analog(2)with CB[8]only generates a 2D SOF with a lower degree of internal order,suggesting that the inherent amphiphilicity of 1 plays a crucial role in improving its 2D self-assembly in aqueous phase.

High mobility organic semiconductors for field-effect transistors

Organic field-effect transistors(OFETs) are attracting more and more attention due to their potential applications in low-cost, large-area and flexible electronic products. Organic semiconductors(OSCs) are the key components of OFETs and basically determine the device performance. The past five years have witnessed great progress of OSCs. OSCs used for OFETs have made rapid progress, with field-effect mobility much larger than that of amorphous silicon(0.5?1.0 cm2/(V s)) and of up to 10 cm2/(V s) or even higher. In this review, we demonstrate the latest progress of OSCs for OFETs, where more than 50 representative OSCs are highlighted and analyzed to give some valuable insights for this important but challenging field.

A heteropore covalent organic framework for adsorptive removal of Cd(Ⅱ) from aqueous solutions with high efficiency

A heteropore covalent organic framework(COF) integrating tetraphenylethene skeleton and catechol segment is designed and synthesized.It exhibits extremely high stability in water under different pH conditions,which makes it an excellent material for adsorptive removal of Cd(Ⅱ) from aqueous solutions with very fast adsorption kinetics,high uptake capacity,and good recyclability.

Designed Synthesis of a Two-Dimensional Covalent Organic Framework with Three-Level Hierarchical Porosity

of main observation and conclusion Covalent organic frameworks(COFs)with hierarchical porosity have drawn considerable attention very recently due to their advantages over the COFs with uniform porosity in some aspects.However,the design strategies for the construction of this type of COFs,namely heteropore COFs,are quite limited.We herein report a facile approach to constructing a two-dimensional COF which possesses three different kinds of pores.Its structure is confirmed by powder X-ray diffraction and nitrogen sorption studies.The successful construction of the triple-pore COF represents a new method to access COFs with high hierarchical porosity.

Effects of connecting sequences of building blocks on reticular synthesis of covalent organic frameworks

The principle of reticular chemistry has been widely used to guide the design of crystalline porous materials such as metal organic frameworks(MOFs)and covalent organic frameworks(COFs).While in the early strategies only the symmetries of the building blocks were considered for reticular synthesis of COFs,recently a few researches on COFs with hierarchical porosities indicate that connecting sequence of building blocks also plays a crucial role in determining crystalline structures of COFs.However,this important phenomenon has not been systematically investigated yet.In this article,a model system has been established to demonstrate how different connecting sequences of two C_(2v)-symmetric building blocks lead to the formation of four two-dimensional(2D)COFs with distinct framework structures.To verify this concept,target synthesis was conducted to produce three COFs,whose structures were confirmed by powder X-ray diffraction and pore size distribution analysis.

n-Channel Organic Transistors Processed from Halogen-Free Solvents： Solvent Effect on Thin-Film Morphology and Charge Transport

Non-chlorinated solvents are highly preferable for organic electronic processing due to their environmentally friendly characteristics. Four different halogen-free solvents, tetrafuran, toluene, meta-xylene and 1,2,4-trimethyl- benzene, were selected to fabricate n-channel organic thin film transistors （OTFTs） based on 3-hexylundecyl sub- stituted naphthalene diimides fused with （1,3-dithiol-2-ylidene）malononitrile groups （NDI3HU-DTYM2）. The OTFTs based on NDI3HU-DTYM2 showed electron mobility of up to 1.37 cm2-V-1·s -1 under ambient condition. This is among the highest device performance for n-channel OTFTs processed from halogen-free solvents. The dif- ferent thin-film morphologies, from featureless low crystalline morphology to well-aligned nanofibres, have a great effect on the device performance. These results might shed some light on solvent selection and the resulting solution process for organic electronic devices.

A Study on Constitutional Isomerism in Covalent Organic Frameworks:Controllable Synthesis,Transformation,and Distinct Difference in Properties

Isomerism is an essential and widespread phenomenon in organic chemistry but rarely observed in covalent organic frameworks(COFs),a novel class of crystalline porous organic polymers with versatile applications.Herein,we give an account of the first example of a controllable synthesis of constitutional isomers of a COF.The two isomers exhibited marked differences in their gas/vapor adsorption behaviors and chemical stability in various solvents.Furthermore,structure transformation from one isomer to the other was realized.This work not only paves the way for rational design and synthesis of COF isomers but also provides a vivid example of structure–property relationship in crystalline porous polymers.

Water-dispersible and soluble porous organic polymers for biomedical applications

Porous organic polymers(POPs)have become an emerging class of advanced porous organic materials owing to their structural diversity and tailored functions in solid state and organic media.Creating water-soluble and related water-dispersible POPs is still very challenging in the research area of porous organic materials.Their porosity-based functions with diverse topological architectures in aqueous media offer promising platforms in bio-related fields.This review highlights recent progress on water soluble or dispersible POPs for biomedical applications including bioimaging and biosensing,nanocarriers for drug delivery and tumor targeting,phototherapeutics,protein and gene delivery,biomacromolecule encapsulation and discrimination,and anti-microbial activity.