Chemically Functionalized Two‐Dimensional Carbon Materials

Nanographenes (NGs), also known as graphene quantum dots, have recently been developed as nanoscale graphene fragments. These nanocarbon species can be excited with UV light and emit light from the UV‐to‐visible region. This photoemission has received great attraction across multiple scientific fields. NGs can be produced by cutting off carbon sources or fusing small organic molecules to grow graphitic structures. Furthermore, the organic synthesis of NGs has been intensely studied. Recently, the number of research papers on postsynthetic modification of NGs has gradually increased. Installed organic groups can tune the properties of NGs and provide new functionalities, opening the door for the development of sophisticated carbon‐based functional materials. This review sheds light on recent progress in the postsynthetic modification of NGs and provides a brief summary of their production methods.     

Assembly and application advancement of organic‐functionalized graphene‐based materials: A review

Owing to the remarkable physicochemical properties such as hydrophobicity, conductivity, elasticity, and light weight, graphene‐based materials have emerged as one of the most appealing carbon allotropes in materials science and chemical engineering. Unfortunately, pristine graphene materials lack functional groups for further modification, severely hindering their practical applications. To render graphene materials with special characters for different applications, graphene oxide or reduced graphene oxide has been functionalized with different organic agents and assembled together, via covalent binding and various noncovalent forces such as π–π interaction, electrostatic interaction, and hydrogen bonding. In this review, we briefly discuss the state‐of‐the‐art synthetic strategies and properties of organic‐functionalized graphene‐based materials, and then, present the prospective applications of organic‐functionalized graphene‐based materials in sample preparation.     

Reductive Amination Reaction for the Functionalization of Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) represent intriguing biopolymeric nanocrystalline materials, that are biocompatible, sustainable and renewable, can be chemically functionalized and are endowed with exceptional mechanical properties. Recently, studies have been performed to prepare CNCs with extraordinary photophysical properties, also by means of their functionalization with organic light-emitting fluorophores. In this paper, we used the reductive amination reaction to chemically bind 4-(1-pyrenyl)butanamine selectively to the reducing termini of sulfated or neutral CNCs (S_CNC and N_CNC) obtained from sulfuric acid or hydrochloric acid hydrolysis. The functionalization reaction is simple and straightforward, and it induces the appearance of the typical pyrene emission profile in the functionalized materials. After a characterization of the new materials performed by ATR-FTIR and fluorescence spectroscopies, we demonstrate luminescence quenching of the decorated N_CNC by copper (II) sulfate, hypothesizing for these new functionalized materials an application in water purification technologies.     

Two-dimensional nanocomposites based on chemically modified graphene

The multiple functional groups and unique two-dimensional (2D) morphology make chemically modified graphene (CMG) an ideal template for the construction of 2D nanocomposites with various organic/inorganic components. Additionally, the recovered electrical conductivity of CMG may provide a fast-electron-transport channel and can thus promote the application of the resultant nanocomposites in optoelectronic and electrochemical devices. This Concept article summarizes the different strategies for the bottom-up fabrication of CMG-based 2D nanocomposites with small organic molecules, polymers, and inorganic nanoparticles, which represent the new directions in the development of graphene-based materials.     

Overcoming the insolubility of carbon nanotubes through high degrees of sidewall functionalization

The use of carbon nanotubes in materials applications has been slowed due to nanotube insolubility and their incompatibility with polymers. We recently developed two protocols to overcome the insoluble nature of carbon nanotubes by affixing large amounts of addends to the nanotube sidewalls. Both processes involve reactions with aryl diazonium species. First, solvent-free functionalization techniques remove the need for any solvent during the functionalization step. This delivers functionalized carbon nanotubes with increased solubility in organic solvents and processibility in polymeric blends. Additionally, the solvent-free functionalization process can be done on large scales, thereby paving the way for use in bulk applications such as in structural materials development. The second methodology involves the functionalization of carbon nanotubes that are first dispersed as individual tubes in surfactants within aqueous media. The functionalization then ensues to afford heavily functionalized nanotubes that do not re-rope. They remain as individuals in organic solvents giving enormous increases in solubility. This protocol yields the highest degree of functionalization we have obtained thus far-up to one in nine carbon atoms on the nanotube has an organic addend. The proper characterization and solubility determinations on nanotubes are critical; therefore, this topic is discussed in detail.     

Halogen-Induced Controllable Cyclizations as Diverse Heterocycle Synthetic Strategy

In organic synthesis, due to their high electrophilicity and leaving group properties, halogens play pivotal roles in the activation and structural derivations of organic compounds. Recently, cyclizations induced by halogen groups that allow the production of diverse targets and the structural reorganization of organic molecules have attracted significant attention from synthetic chemists. Electrophilic halogen atoms activate unsaturated and saturated hydrocarbon moieties by generating halonium intermediates, followed by the attack of carbon-containing, nitrogen-containing, oxygen-containing, and sulfur-containing nucleophiles to give highly functionalized carbocycles and heterocycles. New transformations of halogenated organic molecules that can control the formation and stereoselectivity of the products, according to the difference in the size and number of halogen atoms, have recently been discovered. These unique cyclizations may possibly be used as efficient synthetic strategies with future advances. In this review, innovative reactions controlled by halogen groups are discussed as a new concept in the field of organic synthesis.     

Azulene-based organic functional molecules for optoelectronics

Design and synthesis of new organic functional materials with improved performance or novel properties are of great importance in the field of optoelectronics. Azulene, as a non-alternant aromatic hydrocarbon, has attracted rising attention in the last few years. Different from most common aromatic hydrocarbons, azulene has unique characteristics, including large dipole moment, small gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). However, the design and synthesis of azulene-based functional materials are still facing several challenges. This review focuses on the recent development of organic functional materials employing azulene unit. The synthesis of various functionalized azulene derivatives is summarized and their applications in optoelectronics are discussed, with particular attention to the fields including nonlinear optics (NLO), organic field-effect transistors (OFETs), solar cells, and molecular devices.     

Effects of Edge Functionalization of Nanographenes with Small Aromatic Systems

Regulation of the physical properties of nanographenes (NGs) by edge functionalization is an active research area. We conducted a computational study of the effects of edge functionalization on the physical properties of NGs. The computed NGs were models of experimentally obtained NGs and composed of a C₁₇₄ carbon framework with one to four 3,5-dimethylnaphthalene units on the edge. The effects were assessed structurally, magnetically, and electronically by the least square planarity index, harmonic oscillator model of aromaticity, nucleus-independent chemical shift, and HOMO–LUMO (H–L) gaps. Density functional theory calculations indicate that although the structures of the model NGs are not very sensitive to edge functionalization, but the magnetic and electronic properties are. The installed substituents narrowed the H−L gap and induced a redshift of the photoluminescence (PL) band by the π conjugation between NG and the substituent. These results are consistent with the extension of the absorption band and the redshift of the PL bands of the experimentally modified NGs. Furthermore, the calculations confirmed the contribution of the charge transfer character to the absorption spectra.     

Organic Functionalized Carbon Nanostructures for Solar Energy Conversion

This review presents an overview of the use of organic functionalized carbon nanostructures (CNSs) in solar energy conversion schemes. Our attention was focused in particular on the contribution of organic chemistry to the development of new hybrid materials that find application in dye-sensitized solar cells (DSSCs), organic photovoltaics (OPVs), and perovskite solar cells (PSCs), as well as in photocatalytic fuel production, focusing in particular on the most recent literature. The request for new materials able to accompany the green energy transition that are abundant, low-cost, low-toxicity, and made from renewable sources has further increased the interest in CNSs that meet all these requirements. The inclusion of an organic molecule, thanks to both covalent and non-covalent interactions, in a CNS leads to the development of a completely new hybrid material able of combining and improving the properties of both starting materials. In addition to the numerical data, which unequivocally state the positive effect of the new hybrid material, we hope that these examples can inspire further research in the field of photoactive materials from an organic point of view.     

Graphene Oxide as a Mediator in Organic Synthesis: a Mechanistic Focus

Graphene oxide (GO) is experiencing growing interest by synthetic organic chemists as a promoter of chemical transformations. The synergistic role of the multiple functionalities featuring the nanostructured carbon materials and their π-domains enables the interplay of specific activation modes towards organic compounds that can explore unprecedented chemical modifications. A detailed comprehension of the mechanistic details that govern the transformations guided by GO is a not fully solved task in the field. In this direction, more sophisticated and diversified techniques are employed, providing insights towards intriguing activation modes exerted by the π-matrix and the oxygenated/sulfonate groups decorating the functionalized nano-carbon material. The present Minireview accounts for a critical survey of the most recent developments in the area of GO-mediated organic transformations with a specific focus on mechanist aspects.     

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.     

Computational Studies on the Structures of Nanographenes with Various Edge Functionalities

Computational studies have often been carried out on hydrogen-terminated nanographenes (NGs). These structures are, however, far from those deduced from experimental observations, which have suggested armchair edges with two carboxy groups on the edges as dominant. We conducted computational studies on NGs consisting of C₄₂, C₆₀, C₇₈, C₉₆, C₁₄₂, and C₁₇₄ carbon atoms with hydrogen, carboxy, and N-methyl imide-terminated armchair edges. DFT calculations inform distorted basal planes and similar HOMO-LUMO gaps, indicating that the edge oxidation and functionalization do not very influence the electronic structure. Comparison of observed UV-vis spectra of carboxy- and N-octadecyl chain terminated NGs with calculated spectra of model NGs informs the contribution of π-π* transitions on the basal plane to the absorptions in the visible region. A dimeric structure of NG and octadecyl-installed NG demonstrate that both the distorted basal planes and the steric contacts among the functional groups widen the surface-to-surface distance thereby allowing the invasion of solvent molecules between the surfaces. This picture is consistent with the improved solubility of edge-modified NGs.     

Synthetic Hydrogels with Covalently Incorporated Saccharides Studied for Biomedical Applications – 15 Year Overview

Glycosylated materials have attracted special attention in biomedical field because of the unique properties of the individual carbohydrates in recognition mechanisms in many biological events. Sugar residues decorating a polymer surface can be regarded as multivalent ligands for interaction with various glycoproteins. This phenomenon provides the basis for several biomedical applications; of these, ligand-based targeted therapy is the most frequently cited. Materials functionalized with individual carbohydrates can be used for the selective binding of lectin proteins. Carbohydrate–lectin interactions underpin the development of diverse biosensor devices and bioassays aimed at pathogen detection. Because of the high content of hydroxyl groups and the consequent high hydrophilicity, saccharide-based monomers are perfect candidates for incorporation into hydrogels. Such functionalization allows synthetic materials to acquire unique properties and enhance their performance. This review covers developments over the past 15 years in the field of the synthesis of chemically crosslinked nano-, micro- and bulk hydrogels with covalently incorporated mono-, di- or trisaccharides. A brief view on the potential biomedical applications of these unique hydrogels is provided with particular emphasis on carriers for delivery of bioactive molecules, bioactivated materials for cell culture and tissue engineering as well as capture systems for pathogenic microorganisms.     

Preparation and application of nanocatalysts via surface functionalization of mesoporous materials

Surface immobilization of active species onto mesoporous materials is gaining importance, especially in the design of functionalized mesoporous materials as a nanocatalyst through heterogenization of homogeneous catalytic systems. This article summarizes recent work on the synthesis, characterization and catalytic performance of the functionalized mesoporous catalysts performed by the present authors. A cationic rhenium(I) complex was encapsulated into mesoporous Al-MCM-41 molecular sieve using a ion-exchange method, yielding a new photocatalyst to be active for photocatalytic reduction of CO₂. Surface functionalization of mesoporous silica SBA-15 with sulfonic acid groups was investigated to give a solid acid catalyst. The chemically modified Fe-containing mesoporous materials, which are active for hydroxylation of phenol, were prepared by a surface-grafting method that iron salts are immobilized onto mesoporous Si-MCM-41 with the help of 3-aminopropyltrimethoxysilane as a linker. A cobalt(III) complex was heterogenized onto mesoporous silica SBA-15 containing carboxylic groups in order to utilize as a solid catalyst for the liquid-phase oxidation of aromatic hydrocarbons.     

Fluidics of a nanogap

We have determined the filling properties of nanogaps with chemically heterogeneous walls. The quantitative criteria we present allow the prediction of the liquid loading of the nanostructure. They can easily be applied in combination with contact-angle measurements on planar substrates of the nanogap materials. We present an application of the theory to a recently developed nanogap biosensor. Chemical force microscopy (CFM) is employed to characterize the initial silanol properties of the gap. The functionality of the complex surface chemistry of the biosensor is demonstrated by the observation of functionalized nanoparticles in the gap with its resulting characteristic current-voltage relationship.     

Interfaces between Molecular and Polymeric “Metals”: Electrically Conductive,Structure-Enforced Assemblies of Metallomacrocycles

The design, synthesis, characterization, and understanding of new molecular and macro-molecular substances with “metal-like” electrical properties represents an active research area at the interface of chemistry, physics, and materials science. An important, long-range goal in this field of “materials by design” is to construct supermolecular assemblies which exhibit preordained collective phenomena by virtue of “engineered” interactions between molecular building blocks. In this review, such a class of designed materials is discussed which, in addition, bridges the gap between molecular and polymeric conductors: assemblies of electrically conductive metallomacrocycles. It is seen that efforts to rationally construct stacked metal-like molecular arrays lead logically to structure-enforced macromolecular assemblies of covalently linked molecular subunits. Typical building blocks are robust, chemically versatile metallophthalocyanines. The electrical optical, and magnetic properties of these metallomacrocyclic assemblies and the fragments thereof, provide fundamental information on the connections between local atomic-scale architecture, electronic structure, and the macroscopic collective properties of the bulk solid.     

Preparing a polystyrene‐functionalized multiple‐walled carbon nanotubes via covalently linking acyl chloride functionalities with living polystyryllithium

A new method was developed for preparing polystyrene‐functionalized multiple‐walled carbon nanotubes (MWNTs) through the termination of anionically synthesized living polystyryllithium with the acyl chloride functionalities on the MWNTs. The acyl chloride functionalities on the MWNTs were in turn obtained by the formation of carboxyls via chemical oxidation and their conversion into acyl chlorides. The polystyrene‐functionalized MWNTs had good dispersion in common organic solvents, and this indicated good compatibility for the preparation of styrenic nanocomposite materials. The synthesis results and characterization data for the functionalized MWNTs, collected via Fourier transform infrared, thermogravimetric analysis, solid‐state NMR, and electron microscopy, are presented and discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5802–5810, 2004     

One-Step Synthesis of Janus Fluorographene Derivatives

Fluorographene, a two-dimensional derivative of graphene, is an excellent starting material for the synthesis of graphene derivatives. In this work, a one-step, substrate-free method for the asymmetric functionalization of fluorographene layers with hydroxyl groups by a facile nucleophilic substitution reaction is reported. Such a chemical modification occurs in a biphasic aqueous–organic system under mild conditions, leading to Janus graphene nanosheets functionalized by hydroxyl groups on one side and retaining fluorine atoms on the other. The reported experimental route paves the way for two-dimensional bifacial graphene templates, thus broadening the application potential of graphene materials.