Substrate‐Modulated Reductive Graphene Functionalization

Covalently functionalizing mechanical exfoliated mono‐ and bilayer graphenides with λ‐iodanes led to the discovery that the monolayers supported on a SiO₂ substrate are considerably more reactive than bilayers as demonstrated by statistical Raman spectroscopy/microscopy. Supported by DFT calculations we show that ditopic addend binding leads to much more stable products than the corresponding monotopic reactions as a result of the much lower lattice strain of the reactions products. The chemical nature of the substrate (graphene versus SiO₂) plays a crucial role.     

Cycloaddition of Porphyrins to Isatin: Synthesis of Novel Spiro Porphyrin Derivatives

Isatin undergoes regioselective 1,3‐dipolar cycloaddition reactions with porphyrin azomethine ylides derived from Ni(II) β‐formyl‐meso‐tetraphenylporphyrins in the presence of N‐methylglycine to afford novel spiro porphyrin derivatives.     

Photoinduced Charge‐Transfer Interactions on a Graphene/Block Copolymer Electrostatically Bound to Tetracationic Porphyrin in Aqueous Media

Stable dispersions of exfoliated graphene in aqueous media with the aid of the amphiphilic block copolymer poly(isoprene‐b‐acrylic acid) (PI‐b‐PAA), in the form of its anion, were used to electrostatically bind cationic 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridinio)porphine tetra(p‐toluenesulfonate) (H₂P⁴⁺). A new graphene/PI‐b‐PAA^?–H₂P⁴⁺ ensemble was formed and examined by dynamic light scattering, UV/Vis and fluorescence emission spectroscopy. The efficient fluorescence quenching of H₂P⁴⁺ in the graphene/PI‐b‐PAA^?–H₂P⁴⁺ ensemble was probed by using steady‐state and time‐resolved photoluminescence, suggesting that electron/energy‐transfer phenomena occur within the nanoensemble. Blank experiments validated the concept of electrostatic interactions that govern the formation of graphene/PI‐b‐PAA^?–H₂P⁴⁺ ensemble, which signified the importance of graphene as an electron acceptor toward the preparation of some new donor–acceptor systems. Finally, kinetic analysis of the lifetime profiles of the fluorescence emission gave information regarding the quenching rate constant and quantum yield of the singlet excited state of H₂P⁴⁺ in the graphene/PI‐b‐PAA^?–H₂P⁴⁺ ensemble.     

Selective Functionalization of Graphene at Defect‐Activated Sites by Arylazocarboxylic tert‐Butyl Esters

The development of versatile functionalization concepts for graphene is currently in the focus of research. Upon oxo‐functionalization of graphite, the full surface of graphene becomes accessible for C?C bond formation to introduce out‐of‐plane functionality. Herein, we present the arylation of graphene with arylazocarboxylic tert‐butyl esters, which generates aryl radicals after activation with an acid. Surprisingly, the degree of functionalization is related to the concentration of lattice vacancy defects in the graphene material. Consequently, graphene materials that are free from lattice defects are not reactive. The reaction can be applied to graphene dispersed in solvents and leads to bitopic functionalization as well as monotopic functionalization when the graphene is deposited on surfaces. As the arylazocarboxylic tert‐butyl ester moiety can be attached to various molecules, the presented method paves the way to functional graphene derivatives, with the density of defects determining the degree of functionalization.     

Fluorescent Azasteroids through Ultrasound Assisted Cycloaddition Reactions

We report here the synthesis and optical spectral properties of several new azasteroid derivatives. The formation of these compounds was explained based on the most probable mechanism. The luminescent heterocycles were synthesized by 1,3-dipolar cycloaddition reactions between benzo[f]quinoline and methylpropiolate or dimethyl acetylenedicarboxylate (DMAD). A selective and efficient way for [3+2]-dipolar cycloaddition of benzo[f]quinolinium ylides under ultrasound (US) irradiation (20 kHz processing frequency) is presented. We report substantially higher yields under US irradiation, whereas the solvent amounts required are at least three-fold less compared to classical heating. The azasteroid derivatives are blue emitters with λ_max of fluorescence around 430–450 nm. A certain influence of the azasteroid substituents concerning absorption and fluorescent properties was observed. Compounds anchored with a bulky pivaloyl group or without a C=O carbonyl group have shown increased fluorescence intensity.     

Chemical Functionalisation and Photoluminescence of Graphene Quantum Dots

Chemical modification of graphene quantum dots (GQDs) can influence their physical and chemical properties; hence, the investigation of the effect of organic functional groups on GQDs is of importance for developing GQD–organic hybrid materials. Three peripherally functionalised GQDs having a third‐generation dendritic wedge (GQD‐ 2 ), long alkyl chains (GQD‐ 3 ) and a polyhedral oligomeric silsesquioxane group (GQD‐ 4 ) were prepared by the Cu^I‐catalysed Huisgen cycloaddition reaction of GQD‐ 1 with organic azides. Cyclic voltammetry indicated that reduction occurred on the surfaces of GQD‐ 1 – 4 and on the five‐membered imide rings at the periphery, and this suggested that the functional groups distort the periphery by steric interactions between neighbouring functional groups. The HOMO–LUMO bandgaps of GQD‐ 1 – 4 were estimated to be approximately 2 eV, and their low‐lying LUMO levels (<?3.9 eV) were lower than that of phenyl‐C₆₁‐butyric acid methyl ester, an n‐type organic semiconductor. The solubility of GQD‐ 1 – 4 in organic solvents depends on the functional groups present. The functional groups likely cover the surfaces and periphery of the GQDs, and thus increase their affinity for solvent and avoid precipitation. Similar to GQD‐ 2 , both GQD‐ 3 and GQD‐ 4 emitted white light upon excitation at 360 nm. Size‐exclusion chromatography demonstrated that white‐light emission originates from the coexistence of differently sized GQDs that have different photoluminescence emission wavelengths.     

Luminescent Graphene-Based Materials via Europium Complexation on Dipyridylpyridazine-Functionalized Graphene Sheets

Graphene-based materials exhibit outstanding physical properties and so are potentially applicable in a great variety of fields. Unlike their corresponding oxides, graphite and graphene are not prone to functionalization. Diels–Alder reactions are among the scarce reactions that they can occur without disrupting their conjugated sp² systems. Herein, the reaction between graphite and 3,6-di(2-pyridyl)-1,2,4,5-tetrazine under different conditions affords several graphene-based materials consisting of dipyridylpyridazine-functionalized few-layer graphene, multilayer graphene and graphite, the sheets of which act as ligands for the grafting of a europium complex. These three materials show strong red emission under 365 nm UV radiation. Their emitting particles can be visualized by confocal microscopy. The rich coordination chemistry of dipyridylpyridazine ligands has potential novel properties for similarly functionalized graphene-based materials grafted with other metal complexes.     

Intramolecular 1,3-Dipolar Cycloaddition Reactions

The intramolecular 1,3-dipolar cycloaddition reaction of suitably functionalized 1,3-dipoles represents a general scheme for the synthesis of novel fused ring heterocycles. Such reactions of a number of 1,3-dipoles are summarized and the general outline and potential analogies for these reactions noted. While the immediate aim of this review is to survey and correlate published work, it is hoped that general and specific points in need of study will be revealed and will stimulate further work in this fertile field.     

Covalent Reactions on Chemical Vapor Deposition Grown Graphene Studied by Surface‐Enhanced Raman Spectroscopy

Graphene is a material of unmatched properties and eminent potential in disciplines ranging from physics, to chemistry, to biology. Its advancement to applications with a specific function requires rational design and fine tuning of its properties, and covalent introduction of various substituents answers this requirement. We challenged the obstacle of non‐trivial and harsh procedures for covalent functionalization of pristine graphene and developed a protocol for mild nucleophilic introduction of organic groups in the gas phase. The painstaking analysis problem of monolayered materials was addressed by using surface‐enhanced Raman spectroscopy, which allowed us to monitor and characterize in detail the surface composition. These deliverables provide a toolbox for reactivity of fluorinated graphene under mild reaction conditions, providing structural freedom of the species to‐be‐grafted to the single‐layer graphene.     

Cycloaddition Reactions of Enamines

This review includes information for around two last decades on cycloaddition reactions of enamines with various agents in order to build carbo- and heterocycles. In addition, the review presents organo-catalytic reactions in which enamines are intermediate products generated in situ. This review covers the synthesis of four, five, six and eight-membered carbocyclic compounds, as well as heterocycles as pyrroles, pyridines, etc.     

Thermal Disproportionation of Oxo-Functionalized Graphene

Graphene production by wet chemistry is an ongoing scientific challenge. Controlled oxidation of graphite introduces oxo functional groups; this material can be processed and converted back to graphene by reductive defunctionalization. Although thermal processing yields conductive carbon, a ruptured and undefined carbon lattice is produced as a consequence of CO₂ formation. This thermal process is not understood, but it is believed that graphene is not accessible. Here, we thermally process oxo-functionalized graphene (oxo-G) with a low (4–6 %) and high degree of functionalization (50–60 %) and find on the basis of Raman spectroscopy and transmission electron microscopy performed at atomic resolution (HRTEM) that thermal processing leads predominantly to an intact carbon framework with a density of lattice defects as low as 0.8 %. We attribute this finding to reorganization effects of oxo groups. This finding holds out the prospect of thermal graphene formation from oxo-G derivatives.     

铑催化环加成反应的研究进展

综述了近几年铑催化剂在环加成反应中的研究进展, 主要包括[2＋2], [2＋2＋1], [2＋2＋2], [3＋2], [3＋4]和[4＋2]环加成反应等, 讨论了铑催化下的环加成反应及其机理.     

Study on Unexpected Cycloaddition Reactions of Imines with THF

Thesynthesisofnitrogen-containingheterocylesthroughcycloadditionreactionofimineshasstimulatedmuchpreparativeandmechanisticwork'".Whenweattemptedtosynthesizeapolycycliccompound3byadditionreactionofimineland5-norbornene-2,3-dicarboxylicacid2,however,unexpectedtricycliccompounds4and6wereobtainedinsteadofthedesignedproduct3(Schemcl).Heretetrahydrofuran(THF)servedasthesourceofdihydrofiJranwhichunderwentcycloadditionwithlgiving4and6.Ananalogousreactionwasnotedpreviouslyinthislaboratory'(Scheme2).…     

The Covalent Functionalization of Graphene on Substrates

The utilization of grown or deposited graphene on solid substrates offers key benefits for functionalization processes, but especially to attain structures with a high level of control for electronics and “smart” materials. In this review, we will initially focus on the nature and properties of graphene on substrates, based on the method of preparation. We will then analyze the most relevant literature on the functionalization of graphene on substrates. In particular, we will comparatively discuss radical reactions, cycloadditions, halogenations, hydrogenations, and oxidations. We will especially address the question of how the reactivity of graphene is affected by its morphology (i.e., number of layers, defects, substrate, curvature, etc.).     

Cycloaddition Reactions of Deoxyribosylpropynoates

Pure anomers of either α or β 3-(2-deoxyribofuranosyl)propynoates reacted with the tetramethylcyclobutadiene–aluminum trichloride complex to yield the corresponding diastereoisomeric Dewar benzenes. Thermal- or ultraviolet light–initiated rearrangement gave rise to highly substituted C-aryldeoxyribosides as single anomers. The same compounds as well as other substituted deoxyribosides were obtained also by transition metal–mediated cycloaddition reactions.     

Decomposition of Fluorinated Graphene under Heat Treatment

Fluorination modifies the electronic properties of graphene, and thus it can be used to provide material with on‐demand properties. However, the thermal stability of fluorinated graphene is crucial for any application in electronic devices. Herein, X‐ray photoelectron spectroscopy (XPS), temperature‐programmed desorption (TPD), and Raman spectroscopy were used to address the impact of the thermal treatment on fluorinated graphene. The annealing, at up to 700 K, caused gradual loss of fluorine and carbon, as was demonstrated by XPS. This loss was associated with broad desorption of CO and HF species, as monitored by TPD. The minor single desorption peak of CF species at 670 K is suggested to rationalize defect formation in the fluorinated graphene layer during the heating. However, fluorine removal from graphene was not complete, as some fraction of strongly bonded fluorine can persist despite heating to 1000 K. The role of intercalated H₂O and OH species in the defluorination process is emphasised.     

Preparation,Photophysical and Electrochemical Evaluation of an Azaborondipyrromethene/Zinc Porphyrin/Graphene Supramolecular Nanoensemble

The preparation of an entirely supramolecular, multichromophoric azaborondipyrromethene ( ABDP )/zinc tetraphenylporphyrin ( ZnTPP )/exfoliated graphene ( GR ) nanoensemble was accomplished. The ABDP derivative bears glycol chains for enhancing solubility and a pyridine functionality for allowing coordination with ZnTPP . The ABDP / ZnTPP/GR nanoensemble was characterized in terms of morphology and composition by using complementary microscopy imaging, thermogravimetric analysis, Raman as well as steady-state and time-resolved absorption and emission spectroscopy. The photophysical and electrochemical assessment of ABDP / ZnTPP/GR as well as the binding properties of the ABDP / ZnTPP complex, employed as a reference, are presented. Energy and electron transfer events were observed in ABDP / ZnTPP upon photoexcitation. However, in the case of ABDP / ZnTPP/GR , the graphene-induced aggregation of the chromophores alters their electronic interactions, enhancing the energy/electron transfer process between them.