High-Yield Alkylation and Arylation of Graphene via Grignard Reaction with Fluorographene

Solvent Controlled Generation of Spin Active Polarons in Two-Dimensional Material under UV Light Irradiation

Polarons belong to a class of extensively studied quasiparticles that have found applications spanning diverse fields, including charge transport, colossal magnetoresistance, thermoelectricity, (multi)ferroism, optoelectronics, and photovoltaics. It is notable, though, that their interaction with the local environment has been overlooked so far. We report an unexpected phenomenon of the solvent-induced generation of polaronic spin active states in a two-dimensional (2D) material fluorographene under UV light. Furthermore, we present compelling evidence of the solvent-specific nature of this phenomenon. The generation of spin-active states is robust in acetone, moderate in benzene, and absent in cyclohexane. Continuous wave X-band electron paramagnetic resonance (EPR) spectroscopy experiments revealed a massive increase in the EPR signal for fluorographene dispersed in acetone under UV-light irradiation, while the system did not show any significant signal under dark conditions and without the solvent. The patterns appeared due to the generation of transient magnetic photoexcited states of polaronic character, which encompassed the net 1/2 spin moment detectable by EPR. Advanced ab initio calculations disclosed that polarons are plausibly formed at radical sites in fluorographene which interact strongly with acetone molecules in their vicinity. Additionally, we present a comprehensive scenario for multiplication of polaronic spin active species, highlighting the pivotal role of the photoinduced charge transfer from the solvent to the electrophilic radical centers in fluorographene. We believe that the solvent-tunable polaron formation with the use of UV light and an easily accessible 2D nanomaterial opens up a wide range of future applications, ranging from molecular sensing to magneto-optical devices.

Metal-free regioselective mono- and poly-halogenation of 2-substituted indazoles

An unprecedented metal-free regioselective halogenation of 2H-indazoles has been revealed, which not only realized the highly selective synthesis of mono-halogenated products, but also completed poly-halogenations by fine tuning the reaction conditions. Various mono-/poly-/hetero-halogenated indazoles were obtained in moderate to excellent yields. Notably, this approach features environmentally friendly solvents, mild reaction conditions, simple execution and short reaction time.

Emerging graphene derivatives as active 2D coordination platforms for single-atom catalysts

Single-atom catalysts (SACs) based on graphene derivatives are an emerging and growing class of materials functioning as two-dimensional (2D) metal-coordination scaffolds with intriguing properties. Recently, owing to the rich chemistry of fluorographene, new avenues have opened toward graphene derivatives with selective, spacer-free, and dense functionalization, acting as in-plane or out-of-plane metal coordination ligands. The particular structural features give rise to intriguing phenomena occurring between the coordinated metals and the graphene backbone. These include redox processes, charge transfer, emergence, and stabilization of rare or otherwise unstable metal valence states, as well as metal-support and metal-metal synergism. The vast potential of such systems has been demonstrated as enzyme mimics for cooperative mixed-valence SACs, ethanol fuel cells, and CO2 fixation; however, it is anticipated that their impact will further expand toward diverse fields, e.g., advanced organic transformations, electrochemical energy storage, and energy harvesting.

Recent trends in covalent functionalization of 2D materials

Covalent functionalization of the surface is more crucial in 2D materials than in conventional bulk materials because of their atomic thinness, large surface-to-volume ratio, and uniform surface chemical potential. Because...

Recent Advances in Fluorinated Graphene from Synthesis to Applications: Critical Review on Functional Chemistry and Structure Engineering

Fluorinated graphene (FG), as an emerging member of the graphene derivatives family, has attracted wide attention on account of its excellent performances and underlying applications. The introduction of a fluorine atom, with the strongest electronegativity (3.98), greatly changes the electron distribution of graphene, resulting in a series of unique variations in optical, electronic, magnetic, interfacial properties and so on. Herein, recent advances in the study of FG from synthesis to applications are introduced, and the relationship between its structure and properties is summarized in detail. Especially, the functional chemistry of FG has been thoroughly analyzed in recent years, which has opened a universal route for the functionalization and even multifunctionalization of FG toward various graphene derivatives, which further broadens its applications. Moreover, from a particular angle, the structure engineering of FG such as the distribution pattern of fluorine atoms and the regulation of interlayer structure when advanced nanotechnology gets involved is summarized. Notably, the elaborated structure engineering of FG is the key factor to optimize the corresponding properties for potential applications, and is also an up-to-date research hotspot and future development direction. Finally, perspectives and prospects for the problems and challenges in the study of FG are put forward.

Covalent 2D Patterning, Local Electronic Structure and Polarization Switching of Graphene at the Nanometer Level

A very facile and efficient protocol for the covalent patterning and properties tuning of graphene is reported. Highly reactive fluorine radicals were added to confined regions of graphene directed by laser writing on graphene coated with 1-fluoro-3,3-dimethylbenziodoxole. This process allows for the realization of exquisite patterns on graphene with resolutions down to 200 nm. The degree of functionalization, ranging from the unfunctionalized graphene to extremely high functionalized graphene, can be precisely tuned by controlling the laser irradiation time. Subsequent substitution of the initially patterned fluorine atoms afforded an unprecedented graphene nanostructure bearing thiophene groups. This substitution led to a complete switch of both the electronic structure and the polarization within the patterned graphene regions. This approach paves the way towards the precise modulation of the structure and properties of nanostructured graphene.

Halogen Functionalization in the 2D Material Flatland: Strategies, Properties, and Applications

Given the electronegativity and bonding environment of halogen elements, halogenation (i.e., fluorination, chlorination, bromination, and iodination) serves as a versatile strategy for chemical modifications of materials. The combination of halogens and 2D materials has triggered extensive interests since the first report on graphene fluorination in 2008. Subsequently, scholars consistently conduct pre-, in-process, or posthalogenation modifications of emerging 2D materials to achieve desired properties and broad device applications. They also continuously explore the role of halogens in 2D material functionalization. The multiple advantages introduced by halogen decoration make 2D materials outstanding from each subclass. In this review, an overall retrospect is provided on the research advances in the area of 2D material halogenation, including experimental halogenation strategies, halogen-triggered novel physics and properties, and advanced applications across the studied objects. Future research directions in this area are also proposed.

Transfunctionalization of graphite fluoride engineered polyaniline grafting to graphene for High-Performance flexible supercapacitors

Low energy density is the major obstacle for the practical all-solid-state supercapacitors, which may be raised by the combination of the pseudocapacitance with the electrochemical double-layer capacitance. Although graphene and polyaniline have been demonstrated two effective materials, the synthetic route of graphene and their hybrid mode largely dictated the capacitive performances and cyclability of graphene/polyaniline nanocomposites. Herein, we employed commercial graphite fluoride as the precursor to obtain graphene with a well-preserved carbon lattice. After graphite fluoride functionalization by p-phenylenediamine (pPDA) and in situ oxidative polymerization of anilines, polyaniline (PANI) chains were covalently attached to graphene framework through pPDA bridges. Multiple characterizations were performed to confirm the covalent binding mode between graphene scaffolds and PANI partners, and electrochemical tests unraveled the as-prepared G-pPDA-PANI triads delivered a gravimetric capacitance as high as 638F g^-1 and a further amplified volumetric capacitance (up to 759F cm^-3). The bendable all-solid-state supercapacitors yielded an encouraging energy density of over 18 W   h L^-1 at a power density high to 5,950 W L^-1, while exhibiting an exceptional rate capability, cycling stability and mechanical flexibility.

Suzuki-Miyaura reaction of C-F bonds in fluorographene

We report the first successful covalent modification of fluorographene (FG) based on Suzuki-Miyaura reaction of the C-F bond. The origin of the reaction efficiency of the C-F bond can be linked to the two-dimensional structure of FG and the synergistic effect of a phosphine ligand. This extends the application of the Suzuki reaction of the C-F bond into two-dimensional chemistry.

Tunable one-step double functionalization of graphene based on fluorographene chemistry

Double functionalized graphene derivatives were synthetized by a one-pot reaction of fluorographene with organometallic nucleophiles. Their nucleophilicity governed the preference for grafting and was utilized for tuning the functionalization. This approach paves the way toward the facile, up-scalable and controllable multifunctionalization of graphene.

Microwave Energy Drives "On-Off-On" Spin-Switch Behavior in Nitrogen-Doped Graphene

The established application of graphene in organic/inorganic spin-valve spintronic assemblies is as a spin-transport channel for spin-polarized electrons injected from ferromagnetic substrates. To generate and control spin injection without such substrates, the graphene backbone must be imprinted with spin-polarized states and itinerant-like spins. Computations suggest that such states should emerge in graphene derivatives incorporating pyridinic nitrogen. The synthesis and electronic properties of nitrogen-doped graphene (N content: 9.8%), featuring both localized spin centers and spin-containing sites with itinerant electron properties, are reported. This material exhibits spin-switch behavior (on-off-on) controlled by microwave irradiation at X-band frequency. This phenomenon may enable the creation of novel types of switches, filters, and spintronic devices using sp² -only 2D systems.

Chemical Tuning of Specific Capacitance in Functionalized Fluorographene

Owing to its high surface area and excellent conductivity, graphene is considered an efficient electrode material for supercapacitors. However, its restacking in electrolytes hampers its broader utilization in this field. Covalent graphene functionalization is a promising strategy for providing more efficient electrode materials. The chemistry of fluorographene is particularly attractive as it allows scalable chemical production of useful graphene derivatives. Nevertheless, the influence of chemical composition on the capacitance of graphene derivatives is a largely unexplored field in nanomaterials science, limiting further development of efficient graphene-based electrode materials. In the present study, we obtained well-defined graphene derivatives differing in chemical composition but with similar morphologies by controlling the reaction time of 5-aminoisophthalic acid with fluorographene. The gravimetric specific capacitance ranged from 271 to 391 F g-1 (in 1 M Na2SO4), with the maximum value achieved by a delicate balance between the amount of covalently grafted functional groups and density of the sp2 carbon network governing the conductivity of the material. Molecular dynamics simulations showed that covalent grafting of functional groups with charged and ionophilic/hydrophilic character significantly enhanced the ionic concentration and hydration due to favorable electrostatic interactions among the charged centers and ions/water molecules. Therefore, conductive and hydrophilic graphitic surfaces are important features of graphene-based supercapacitor electrode materials. These findings provide important insights into the role of chemical composition on capacitance and pave the way toward designing more efficient graphene-based supercapacitor electrode materials.

Highly Thermally Conductive Fluorinated Graphene Films with Superior Electrical Insulation and Mechanical Flexibility

Graphene-based heat-spreading films have captured high attention in academic study and commercial applications because of their extremely high thermal conductivity and desired flexibility. However, the electrical conductivity limits their utilizations in many electronic fields. Herein, to address this problem, fluorinated graphene (F-graphene) that is exfoliated from commercial fluorinated graphite was first used to prepare the flexible free-standing composite film via vacuum filtration of uniform poly(vinyl alcohol)-assisted F-graphene suspension. The well-organized alignment of F-graphene lamellas makes the composite film show an ultrahigh in-plane thermal conductivity of 61.3 W m^-1 K^-1 at 93 wt % F-graphene. Despite at such high filler loading, the fabricated F-graphene film still possesses a superior electrical insulation property. Therefore, these results suggest that F-graphene, as the novel thermally conductive filler, demonstrates fascinating characters in the preparation of a thermally conductive yet electrically insulating nanocomposite.

Multilayer graphene functionalized through thermal 1,3-dipolar cycloadditions with imino esters: a versatile platform for supported ligands in catalysis

Multilayer graphene (MLG), obtained by mild sonication of graphite in NMP or pyridine, was fully characterized via atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoemission spectroscopy (XPS). Then, it was functionalized via 1,3-dipolar cycloaddition with azomethine ylides generated by thermal 1,2-prototropy of various imino esters. The resulting MLG, containing substituted proline-based amine functions, was characterized by XPS and it showed high nitrogen loading, ranging from 0.6 to 4.2 at% depending on the imino ester used. Among these functionalized MLGs a probe sample was subjected to ester hydrolysis and used as a heterogeneous N,O-chelating ligand to coordinate iridium atomic centers. This supported complex was also characterized by XPS and its catalytic activity was tested in the hydrogen transfer reduction of acetophenone, obtaining up to 85% yield. Furthermore, this catalyst could be recycled up to four times.

Alkynylation of graphene via the Sonogashira C-C cross-coupling reaction on fluorographene

We report successful grafting of alkynyl groups onto graphene via the Sonogashira reaction between fluorographene and terminal alkynes.

We report successful grafting of alkynyl groups onto graphene via the Sonogashira reaction between fluorographene and terminal alkynes. Theoretical calculations revealed that fluorographene can efficiently bind and oxidize the palladium catalyst on electrophilic sites activated by fluorine atoms. This paves the way towards conductive and mechanically robust 3D covalent networks.

The Friedel-Crafts reaction of fluorinated graphene for high-yield arylation of graphene

Herein, we report the Friedel-Crafts reaction of fluorinated graphene with aryl molecules including methylbenzene, chlorobenzene and polystyrene. The reaction achieved the high-yield arylation functionalization of graphene under mild reaction conditions and extends the range of the Friedel-Crafts reaction to the field of two-dimensional materials.

Sulfanilic Acid Pending on a Graphene Scaffold: Novel, Efficient Synthesis and Much Enhanced Polymer Solar Cell Efficiency and Stability Using It as a Hole Extraction Layer

In this contribution, we describe a novel, facile, and scalable methodology for high degree functionalization toward graphene by the reaction between bulk graphite fluoride and in situ generated amine anion. Using this, the rationally designed sulfanilic acid pending on a graphene scaffold (G-SO₃H), a two-dimensional (2D) π-conjugated counterpart of poly(styrenesulfonate), is available. Combined reliable characterizations demonstrate that a very large quantity of sulfanilic blocks are linked to graphene through the foreseen substitution of carbon-fluorine units and an unexpected reductive defluorination simultaneously proceeds during the one-step reaction, endowing the resultant G-SO₃H with splendid dispersity in various solvents and film-forming property via the former, and with recovered 2D π-conjugation via the latter. Besides, the work function of G-SO₃H lies at -4.8 eV, well matched with the P3HT donor. Awarded with these fantastic merits, G-SO₃H behaves capable in hole collection and transport, indicated by the enhanced device efficiency and stability of polymer solar cells (PSCs) based on intensively studied P3HT:PCBM blends as an active layer. In particular, comparison with conventional poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) and recently rising and shining graphene oxide, G-SO₃H outperforms above 17 and 24%, respectively, in efficiency. More impressively, when these three unencapsulated devices are placed in a N₂-filled glovebox at around 25 °C for 7 weeks, or subject to thermal treatment at 150 °C for 6 h also in N₂ atmosphere, or even rudely exposed to indoor air, G-SO₃H-based PSCs exhibit the best stability. These findings enable G-SO₃H to be a strongly competitive alternative of the existing hole extraction materials for PSC real-life applications.

2D Chemistry: Chemical Control of Graphene Derivatization

Controllable synthesis of graphene derivatives with defined composition and properties represents the holy grail of graphene chemistry, especially in view of the low reactivity of graphene. Recent progress in fluorographene (FG) chemistry has opened up new routes for synthesizing a plethora of graphene derivatives with widely applicable properties, but they are often difficult to control. We explored nucleophilic substitution on FG combining density functional theory calculations with experiments to achieve accurate control over the functionalization process. In-depth analysis revealed the complexity of the reaction and identified basic rules for controlling the 2D chemistry. Their application, that is, choice of solvent and reaction time, enabled facile control over the reaction of FG with N-octylamine to form graphene derivatives with tailored content of the alkylamine functional group (2.5-7.5% N atomic content) and F atoms (31.5-3.5% F atomic content). This work substantially extends prospects for the controlled covalent functionalization of graphene.

Graphene and its derivatives as biomedical materials: future prospects and challenges

Graphene and its derivatives possess some intriguing properties, which generates tremendous interests in various fields, including biomedicine. The biomedical applications of graphene-based nanomaterials have attracted great interests over the last decade, and several groups have started working on this field around the globe. Because of the excellent biocompatibility, solubility and selectivity, graphene and its derivatives have shown great potential as biosensing and bio-imaging materials. Also, due to some unique physico-chemical properties of graphene and its derivatives, such as large surface area, high purity, good bio-functionalizability, easy solubility, high drug loading capacity, capability of easy cell membrane penetration, etc., graphene-based nanomaterials become promising candidates for bio-delivery carriers. Besides, graphene and its derivatives have also shown interesting applications in the fields of cell-culture, cell-growth and tissue engineering. In this article, a comprehensive review on the applications of graphene and its derivatives as biomedical materials has been presented. The unique properties of graphene and its derivatives (such as graphene oxide, reduced graphene oxide, graphane, graphone, graphyne, graphdiyne, fluorographene and their doped versions) have been discussed, followed by discussions on the recent efforts on the applications of graphene and its derivatives in biosensing, bio-imaging, drug delivery and therapy, cell culture, tissue engineering and cell growth. Also, the challenges involved in the use of graphene and its derivatives as biomedical materials are discussed briefly, followed by the future perspectives of the use of graphene-based nanomaterials in bio-applications. The review will provide an outlook to the applications of graphene and its derivatives, and may open up new horizons to inspire broader interests across various disciplines.

Reactivity of fluorographene is triggered by point defects: beyond the perfect 2D world

Preparation of graphene derivatives using fluorographene (FG) as a precursor has become a key strategy for the large-scale synthesis of new 2-D materials (e.g. graphene acid, cyanographene, allyl-graphene) with tailored physicochemical properties. However, to gain full control over the derivatization process, it is essential to understand the reaction mechanisms and accompanying processes that affect the composition and structure of the final products. Despite the strength of C-F bonds and high chemical stability of perfluorinated hydrocarbons, FG is surprisingly susceptible to reactions under ambient conditions. There is clear evidence that nucleophilic substitution on FG is accompanied by spontaneous defluorination, and solvent-induced defluorination can occur even in the absence of any nucleophilic agent. Here, we show that distributed radical centers (fluorine vacancies) on the FG surface need to be taken into account in order to rationalize the defluorination mechanism. Depending on the environment, these radical centers can react as electron acceptors, electrophilic sites and/or cause homolytic bond cleavages. We also propose a new radical mechanism of FG defluorination in the presence of N,N'-dimethylformamide (DMF) solvent. Spin-trap experiments as well as 19F NMR measurements unambiguously confirmed formation of N,N'-dimethylformyl radicals and also showed that N,N'-dimethylcarbamoyl fluoride plays a key role in the proposed mechanism. These findings imply that point defects in 2D materials should be considered as key factor determining their chemical properties and reactivity.

Chemistry of Graphene Derivatives: Synthesis, Applications, and Perspectives

The chemistry of graphene and its derivatives is one of the hottest topics of current material science research. The derivatisation of graphene is based on various approaches, and to date functionalization with halogens, hydrogen, various functional groups containing oxygen, sulfur, nitrogen, phosphorus, boron, and several other elements have been reported. Most of these functionalizations are based on sp³ hybridization of carbon atoms in the graphene skeleton, which means the formation of out-of-plane covalent bonds. Several elements were also reported for substitutional modification of graphene, where the carbon atoms are substituted with atoms like nitrogen, boron, and several others. From tens of functional groups, for only two of them were reported full functionalization of graphene skeleton and formation of its stoichiometric counterparts, fluorographene and hydrogenated graphene. The functionalization of graphene is crucial for most of its applications including energy storage and conversion devices, electronic and optic applications, composites, and many others.

Nano-sized paramagnetic and fluorescent fluorinated carbon fiber with high NIR absorbance for cancer chemo-photothermal therapy

We report a novel strategy to synthesize nano-sized, water-soluble and functionalized fluorinated carbon fiber oxide with high fluorescence, paramagnetism and NIR absorption for cancer chemo-photothermal therapy.

Fluorographite to hydroxy graphene to graphene: a simple wet chemical approach for good quality graphene

Good quality graphene is prepared in a scalable manner from fluorographite by nucleophilic substitution of F with OH⁻ ions.

Radical mechanism of a nucleophilic reaction depending on a two-dimensional structure

The mechanism of nucleophilic substitution deserves more investigation to include more reaction systems such as two-dimensional (2D) materials. In this study, we used fluorinated graphene (FG) as a representative 2D material to reveal the in-depth mechanism of its defluorination and nucleophilic substitution reaction under attack of common nucleophiles to explore the chemistry of 2D materials and enrich the research on the nucleophilic substitution reaction. DFT calculations and electron paramagnetic resonance spectroscopy (EPR) demonstrated that defluorination of FG occurred via a radical mechanism after a single electron transfer (SET) reaction between the nucleophile and C-F bond, and a spin center was generated on the nanosheet and fluorine anion. Moreover, neither the S_N1 nor S_N2 mechanism was suggested to be appropriate for the substitution reaction of FG with a 2D structure due to the corresponding kinetics or thermodynamics disadvantage; hence, its nucleophilic substitution was proved to occur via a radical mechanism initiated by the defluorination step. The proposed substitution mechanism of FG demonstrates that nucleophilic substitution via a radical mechanism can also be applied to the attacking process of common nucleophiles without any particular conditions. Furthermore, it has been discovered that triethylamine without active hydrogen can be covalently attached to graphene nanosheets via a nucleophilic substitution reaction with FG; this further indicates a radical process for the nucleophilic substitution of FG rather than an S_N1 or S_N2 mechanism. The detailed process of the nucleophilic substitution reaction of FG was revealed to occur via a radical mechanism depending on the 2D structure of FG, which could also represent the typical characteristic of 2D chemistry.

Chemistry, properties, and applications of fluorographene

Fluorographene, formally a two-dimensional stoichiometric graphene derivative, attracted remarkable attention of the scientific community due to its extraordinary physical and chemical properties. We overview the strategies for the preparation of fluorinated graphene derivatives, based on top-down and bottom-up approaches. The physical and chemical properties of fluorographene, which is considered as one of the thinnest insulators with a wide electronic band gap, are presented. Special attention is paid to the rapidly developing chemistry of fluorographene, which was advanced in the last few years. The unusually high reactivity of fluorographene, which can be chemically considered perfluorinated hydrocarbon, enables facile and scalable access to a wide portfolio of graphene derivatives, such as graphene acid, cyanographene and allyl-graphene. Finally, we summarize the so far reported applications of fluorographene and fluorinated graphenes, spanning from sensing and bioimaging to separation, electronics and energy technologies.

Cyanographene and Graphene Acid: Emerging Derivatives Enabling High-Yield and Selective Functionalization of Graphene

Efficient and selective methods for covalent derivatization of graphene are needed because they enable tuning of graphene's surface and electronic properties, thus expanding its application potential. However, existing approaches based mainly on chemistry of graphene and graphene oxide achieve only limited level of functionalization due to chemical inertness of the surface and nonselective simultaneous attachment of different functional groups, respectively. Here we present a conceptually different route based on synthesis of cyanographene via the controllable substitution and defluorination of fluorographene. The highly conductive and hydrophilic cyanographene allows exploiting the complex chemistry of -CN groups toward a broad scale of graphene derivatives with very high functionalization degree. The consequent hydrolysis of cyanographene results in graphene acid, a 2D carboxylic acid with pK_a of 5.2, showing excellent biocompatibility, conductivity and dispersibility in water and 3D supramolecular assemblies after drying. Further, the carboxyl groups enable simple, tailored and widely accessible 2D chemistry onto graphene, as demonstrated via the covalent conjugation with a diamine, an aminothiol and an aminoalcohol. The developed methodology represents the most controllable, universal and easy to use approach toward a broad set of 2D materials through consequent chemistries on cyanographene and on the prepared carboxy-, amino-, sulphydryl-, and hydroxy- graphenes.

Current and future directions in electron transfer chemistry of graphene

The participation of graphene in electron transfer chemistry, where an electron is transferred between graphene and other species, encompasses many important processes that have shown versatility and potential for use in important applications.

Defluorination and covalent grafting of fluorinated graphene with TEMPO in a radical mechanism

The work innovatively reveals the radical mechanism of derivative reactions of fluorinated graphene including its defluorination and covalent grafting, meanwhile first confirming the destination of deciduous fluorine atoms after defluorination.