Noncovalent wrapping of chemically modified graphene with π-conjugated disk-like molecules

A facile and scalable preparation of dispersion of isolated graphene in various organic solvents has been developed by combining between covalent and noncovalent functionalizations of the graphene surface. Covalently functionalized graphene (FRG) was prepared by the reaction of partially reduced graphene oxide with aryl diazonium salts, followed by the graphene oxide being completely reduced with hydrazine. The resulting FRG disperse readily in organic solvents such as N,N′-dimethylformamide (DMF) and N-methyl-2-pyrrolidinone and the functionalization of graphene was characterized by Fourier transform infrared spectroscopy, thermogravimetric thermogram, X-ray photoelectron spectroscopy, and Raman spectroscopy. The hydrophobic surface of FRG was noncovalently wrapped with aromatic hexakis-dodecylhexa-peri-benzocorone (HBC) by simply mixing of dispersion of FRG in DMF with toluene solution of HBC. The complexation of FRG and HBC was monitored by viewing the absorption and fluorescence spectral changes. Atomic force microscopic images confirmed that graphene was covalently and noncovalently functionalized, while keeping a two-dimensional sheet shape.     

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.     

Sulfur‐Annulated Hexa‐peri‐hexabenzocoronene Decorated with Phenylthio Groups at the Periphery

The chemical nature of the edge periphery essentially determines the physical properties of graphene. As a molecular‐level model system, large polycyclic aromatic hydrocarbons, that is, so‐called nanographenes, can be chemically modified through either edge functionalization or doping with heteroatoms. Although the synthetic methods for edge substitution are well‐developed, incorporation with heteroatoms by the bay annulation of large PAHs remains an enormous challenge. In this study, we present a feasible peripheral sulfur annulation of hexa‐peri‐hexabenzocoronene (HBC) by thiolation of perchlorinated HBC. The tri‐sulfur‐annulated HBC and di‐sulfur‐annulated HBC decorated with phenylthio groups were obtained and characterized by X‐ray diffraction, revealing their distinct sulfur‐annulated peripheral structure. Associated with theoretical calculations, we propose that the regioselective sulfur annulation results from the minimization of strain in the aromatic backbone. We further demonstrate the structure‐correlated property modulation by sulfur annulation, manifested by a decrease in band gap and tunable redox activity.     

Dispersion of Reduced Graphene Oxide in Multiple Solvents with an Imidazolium‐Modified Hexa‐peri‐hexabenzocoronene

An imidazolium‐modified hexa‐peri‐hexabenzocoronene derivative (HBC‐C₁₁‐MIM[Cl^?]) was designed and synthesized as a stabilizer to fabricate reduced graphene oxide (RGO). The resulting RGO/HBC‐C₁₁‐MIM[Cl^?] hybrid shows excellent dispersivity (5.0 mg mL^?1) and stability in water. RGO/HBC‐C₁₁‐MIM[Cl^?] was comprehensively characterized by using atomic force microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and Raman spectroscopy, thus revealing that one HBC‐C₁₁‐MIM[Cl^?] group can stabilize about 178 carbon atoms on the graphene sheets. The obtained hybrid film exhibits a high conductivity of 286 S m^?1. Furthermore, the HBC‐C₁₁‐MIM[Cl^?]‐modified RGO sheets can be readily dispersed in polar organic solvents upon exchange of the hydrophilic Cl^? ions for hydrophobic bis(trifluoromethylsulfonyl) amide (NTf₂^?) ions.     

Exfoliation of Graphite into Graphene in Polar Solvents Mediated by Amphiphilic Hexa‐peri‐hexabenzocoronene

A water‐soluble surfactant consisting of hexa‐peri‐hexabenzocoronene (HBC) as hydrophobic aromatic core and hydrophilic carboxy substituents was synthesized. It exhibited a self‐assembled nanofiber structure in the solid state. Profiting from the π interactions between the large aromatic core of HBC and graphene, the surfactant mediated the exfoliation of graphite into graphene in polar solvents, which was further stabilized by the bulky hydrophilic carboxylic groups. A graphene dispersion with a concentration as high as 1.1 mg L^?1 containing 2–6 multilayer nanosheets was obtained. The lateral size of the graphene sheets was in the range of 100–500 nm based on atomic force microscope (AFM) and transmission electron microscope (TEM) measurements.     

Reductive C2‐Alkylation of Pyridine and Quinoline N‐Oxides Using Wittig Reagents

The ability to alkylate pyridines and quinolines is important for their further development as pharmaceuticals and agrochemicals, and for other purposes. Herein we describe the unprecedented reductive alkylation of pyridine and quinoline N‐oxides using Wittig reagents. A wide range of pyridine and quinoline N‐oxides were converted into C2‐alkylated pyridines and quinolines with excellent site selectivity and functional‐group compatibility. Sequential C?H functionalization reactions of pyridine and quinoline N‐oxides highlight the utility of the developed method. Detailed labeling experiments were performed to elucidate the mechanism of this process.     

Practical Alkoxythiocarbonyl Auxiliaries for Iridium(I)‐Catalyzed C−H Alkylation of Azacycles

The development of new and practical 3‐pentoxythiocarbonyl auxiliaries for Ir^I‐catalyzed C−H alkylation of azacycles is described. This method allows for the α‐C−H alkylation of a variety of substituted pyrrolidines, piperidines, and tetrahydroisoquinolines through alkylation with alkenes. While the practicality of these simple carbamate‐type auxiliaries is underscored by the ease of installation and removal, the method's utility is demonstrated in its ability to functionalize biologically relevant l ‐proline and l ‐trans ‐hydroxyproline, delivering unique 2,5‐dialkylated amino acid analogues that are not accessible by other C−H functionalization methods.     

A Simple Synthesis of Polyfunctionalized 4‐Aminopyrazolidin‐3‐ones as ‘Aza‐deoxa’ Analogs of D‐Cycloserine

A simple five‐step synthesis of fully substituted (4RS,5RS)‐4‐aminopyrazolidin‐3‐ones as analogs of D ‐cycloserine was developed. It comprises a two‐step preparation of 5‐substituted (4RS,5RS)‐4‐(benzyloxycarbonylamino)pyrazolidin‐3‐ones, reductive alkylation at N(1), alkylation of the amidic N(2) with alkyl halides, and simultaneous hydrogenolytic deprotection/reductive alkylation of the primary NH₂ group. The synthesis enables an easy stepwise functionalization of the pyrazolidin‐3‐one core with only two types of common reagents, aldehydes (or ketones) and alkyl halides. The structures of products were elucidated by NMR spectroscopy and X‐ray diffraction.     

Construction of an Internally B3N3‐Doped Nanographene Molecule

The synthesis of a hexa‐peri‐hexabenzocoronene (HBC) with a central borazine core is described. The solid‐state structure of this BN‐doped HBC (BN‐HBC) is isotypic with that of the parent HBC. Scanning tunneling microscopy shows that BN‐HBC lies flat on Au(111) in a two‐dimensional pattern.     

Functionalization and Rearrangement of Spirocyclohexadienyl Oxindoles: Experimental and Theoretical Investigations

The preparation and functionalization of spirocyclohexa‐2,5‐diene oxindoles is described. The spirocyclic core of the title compounds was installed by using a SmI₂‐mediated cyclization of aryl iodobenzamides. Epoxidation with CF₃CO₃H was then carried out and was shown to occur with a high level of diastereocontrol: the reagent approaches the diene moiety syn to the amide group, which is likely to be as a consequence of hydrogen bonding between the amide C?O bond and the peracid hydrogen. Carbanionic functionalization of the spirocyclohexa‐2,5‐diene oxindoles was then examined, leading to an unprecedented rearrangement of the strained spiro system into dearomatized phenanthridinones. Upon treatment with lithium diisopropylamide (LDA) at ?40 °C, the dienes rearranged to provide a phenanthridinone lithium enolate intermediate that was trapped by electrophiles including alkyl halides and aldehydes. Interestingly, alkylation and hydroxyalkylation occurred with different regiocontrol. DFT calculations were performed that rationalize the observed skeleton rearrangement, emphasizing the role of LDA/diisopropylamine in this rearrangement. The proposed mechanism thus relies on a thermodynamically driven diisopropylamine‐mediated proton transfer with the cleavage of the diene–amide C?O bond as the key step.     

Functionalization of Hydrogenated Graphene: Transition‐Metal‐Catalyzed Cross‐Coupling Reactions of Allylic C−H Bonds

The chemical functionalization of hydrogenated graphene can modify its physical properties and lead to better processability. Herein, we describe the chemical functionalization of hydrogenated graphene through a dehydrogenative cross‐coupling reaction between an allylic C?H bond and the α‐C?H bond of tetrahydrothiophen‐3‐one using Cu(OTf)₂ as the catalyst and DDQ as the oxidant. The chemical functionalization was confirmed by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy and visualized by scanning electron microscopy. The functionalized hydrogenated graphene material demonstrated improved dispersion stability in water, bringing new quality to the elusive hydrogenated graphene (graphane) materials. Hydrogenated graphene provides broad possibilities for chemical modifications owing to its reactivity.     

Spatially Resolved Bottom‐Side Fluorination of Graphene by Two‐Dimensional Substrate Patterning

Patterned functionalization can, on the one hand, open the band gap of graphene and, on the other hand, program demanding designs on graphene. The functionalization technique is essential for graphene‐based nanoarchitectures. A new and highly efficient method was applied to obtain patterned functionalization on graphene by mild fluorination with spatially arranged AgF arrays on the structured substrate. Scanning Raman spectroscopy (SRS) and scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy (SEM‐EDS) were used to characterize the functionalized materials. For the first time, chemical patterning on the bottom side of graphene was realized. The chemical nature of the patterned functionalization was determined to be the ditopic scenario with fluorine atoms occupying the bottom side and moieties, such as oxygen‐containing groups or hydrogen atoms, binding on the top side, which provides information about the mechanism of the fluorination process. Our strategy can be conceptually extended to pattern other functionalities by using other reactants. Bottom‐side patterned functionalization enables utilization of the top side of a material, thereby opening up the possibilities for applications in graphene‐based devices.     

Incorporation of Hexa‐peri‐hexabenzocoronene (HBC) into Carbazole–Benzo‐2,1,3‐thiadiazole Copolymers to Improve Hole Mobility and Photovoltaic Performance

Hexa‐peri‐hexabenzocoronene (HBC) is a discotic‐shaped conjugated molecule with strong π–π stacking property, high intrinsic charge mobility, and good self‐assembly properties. For a long time, however, organic photovoltaic (OPV) solar cells based on HBC demonstrated low power conversion efficiencies (PCEs). In this study, two conjugated terpolymers, poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5′‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT)‐ 5 HBC and PCDTBT‐ 10 HBC, were synthesized by incorporating different amounts of HBC as the third component into poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5′‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT) through Suzuki coupling polymerization. For comparison, the donor–acceptor (D –A) conjugated dipolymer PCDTBT was also synthesized to investigate the effect of HBC units on conjugated polymers. The HBC‐containing polymers exhibited higher thermal stabilities, broader absorption spectra, and lower highest‐occupied molecular orbital (HOMO) energy levels. In particular, the field‐effect mobilities were enhanced by more than one order of magnitude after the incorporation of HBC into the conjugated polymer backbone on account of increased interchain π–π stacking interactions. The bulk heterojunction (BHJ) polymer solar cells (PSCs) fabricated with the polymers as donor and PC₇₁BM as acceptor demonstrated gradual improvement of open‐circuit voltage (V_OC) and short‐circuit current (J_SC) with the increase in HBC content. As a result, the PCEs were improved from 3.21 % for PCDTBT to 3.78 % for PCDTBT‐ 5 HBC and then to 4.20 % for PCDTBT‐ 10 HBC.     

Diverse meta‐C−H Functionalization of Arenes across Different Linker Lengths

Arenes containing conformationally flexible long alkyl chains have been successfully functionalized at the meta‐position. Good to excellent meta selectivity is achieved for systems with up to 20 atoms between the target C?H bond and the coordinating heteroatom of the directing group. The palladium‐catalyzed functionalization reactions include alkylation, cyanation, olefination, and acetoxylation. The meta selectivity is exclusively governed by the design of flexible pyrimidine‐based scaffolds.     

Selective Nitrogen Functionalization of Graphene by Bucherer‐Type Reaction

Nitrogen functionalization of graphene offers new hybrid materials with improved performance for important technological applications. Despite studies highlighting the dependence of the performance of nitrogen‐functionalized graphene on the types of nitrogen functional groups that are present, precise synthetic control over their ratio is challenging. Herein, the synthesis of nitrogen‐functionalized graphene rich in amino groups by a Bucherer‐type reaction under hydrothermal conditions is reported. The efficiency of the synthetic method under two hydrothermal conditions was examined for graphite oxide produced by Hummers and Hofmann oxidation routes. The morphological and structural properties of the amino‐functionalized graphene were fully characterized. The use of a synthetic method with a well‐known mechanism for derivatization of graphene will open new avenues for highly reproducible functionalization of graphene materials.     

Copper‐Catalyzed Alkylarylation of Unactivated Alkenes: Synthesis of 3‐Alkyl Indolines from N‐Allyl Anilines and Alkanes

A rare example of C(sp³)?H functionalization of simple alkanes with unactivated alkenes is presented. In the presence of a copper salt and di‐tert‐butyl peroxide (DTBP), N‐allyl anilines underwent exo‐selective alkylation/cyclization cascade with unactivated alkenic bonds as radical acceptors and simple alkanes as radical precursors, providing a direct access to 3‐alkyl indolines. The present protocol features simple operation, broad substrate scope and great exo selectivity.     

Copper‐Catalyzed Regioselective Cascade Alkylation and Cyclocondensation of Quinoline N‐Oxides with Diazo Esters: Direct Access to Conjugated π‐Systems

An inexpensive copper‐catalyzed cascade regioselective alkylation, followed by cyclocondensation of quinoline N‐oxides with α‐diazo esters has been achieved successfully to provide heteroarene‐containing conjugated π‐systems. The developed method is simple, straightforward, and economical with a broad range of substrate scope. The dual role of copper catalyst in the C?H bond functionalization and in Lewis acid‐promoted cyclization was explored.     

Thiol–Yne Click Reactions on Alkynyl–Dopamine‐Modified Reduced Graphene Oxide

The large‐scale preparation of graphene is of great importance due to its potential applications in various fields. We report herein a simple method for the simultaneous exfoliation and reduction of graphene oxide (GO) to reduced GO (rGO) by using alkynyl‐terminated dopamine as the reducing agent. The reaction was performed under mild conditions to yield rGO functionalized with the dopamine derivative. The chemical reactivity of the alkynyl function was demonstrated by post‐functionalization with two thiolated precursors, namely 6‐(ferrocenyl)hexanethiol and 1H,1H,2H,2H‐perfluorodecanethiol. X‐ray photoelectron spectroscopy, UV/Vis spectrophotometry, Raman spectroscopy, conductivity measurements, and cyclic voltammetry were used to characterize the resulting surfaces.     

A Three‐Dimensional Capsule‐like Carbon Nanocage as a Segment Model of Capped Zigzag [12,0] Carbon Nanotubes: Synthesis,Characterization, and Complexation with C70

Herein we report the synthesis and photophysical and supramolecular properties of a novel three‐dimensional capsule‐like hexa‐peri‐hexabenzocoronene (HBC)‐containing carbon nanocage, tripodal‐[2]HBC, which is the first synthetic model of capped zigzag [12,0] carbon nanotubes (CNTs). Tripodal‐[2]HBC was synthesized by the palladium‐catalyzed coupling of triboryl hexabenzocoronene and L‐shaped cyclohexane units, followed by nickel‐mediated C−Br/C−Br coupling and subsequent aromatization of the cyclohexane moieties. The physical properties of tripodal‐[2]HBC and its supramolecular host–guest interaction with C₇₀ were further studied by UV/Vis and fluorescence spectroscopy. Theoretical calculations revealed that the strain energy of tripodal‐[2]HBC was as high as 55.2 kcal mol⁻¹.     

Visible Light‐Induced Decarboxylative Alkylation of Heterocyclic Aromatics with Carboxylic Acids via Anthocyanin as a Photocatalyst

A visible light‐induced decarboxylative alkylation of heterocyclic aromatics with aliphatic carboxylic acids was developed by using anthocyanins as a photocatalyst under mild conditions. A series of alkylated heterocyclic compounds were obtained in moderate to good yields by using the metal‐free decarboxylative coupling reaction under blue light. This strategy uses cheap and readily available carboxylic acids as alkylation reagents with good functional group tolerance and environmental friendliness. It is worth noting that this is the first time that anthocyanin has been used to catalyze the Minisci‐type C?H alkylation. The mechanism of decarboxylation alkylation was studied by capturing the adduct of alkyl radical and hydroquinone, thus confirming a radical mechanism. This protocol provides an alternative visible light‐induced decarboxylative alkylation for the functionalization of heterocyclic aromatics.