Andreas Hirsch

Functionalization of Single-Walled Carbon Nanotubes

Through chemical functionalization of single-walled carbon nanotubes, the prerequisites for possible applications of such nanostructures are established. The derivatized tubes differ from the crude materials in their good solubility, which enables both a more extensive characterization and subsequent chemical reactivity. Current derivatization methods include defect and covalent sidewall functionalization, as well as noncovalent exo- and endohedral functionalization. In this way, for example, a range of nanotubes can be prepared: with sidewall substituents, wrapped with polymers, or with guest molecules included. The current state of the literature is presented in this Minireview.

Sidewall Functionalization of Carbon Nanotubes

The addition of nitrenes, nucleophilic carbenes, and radicals affords soluble, individual single-walled nanotubes (shown here is a carbene-functionalized adduct) by covalent sidewall functionalization. The characterization, a fundamental problem in nanotube chemistry, is simple to carry out.

Covalent bulk functionalization of graphene

Graphene, a truly two-dimensional and fully π-conjugated honeycomb carbon network, is currently evolving into the most promising successor to silicon in micro- and nanoelectronic applications. However, its wider application is impeded by the difficulties in opening a bandgap in its gapless band-structure, as well as the lack of processability in the resultant intrinscially insoluble material. Covalent chemical modification of the π-electron system is capable of addressing both of these issues through the introduction of variable chemical decoration. Although there has been significant research activity in the field of functionalized graphene, most work to date has focused on the use of graphene oxide. In this Article, we report on the first wet chemical bulk functionalization route beginning with pristine graphite that does not require initial oxidative damage of the graphene basal planes. Through effective reductive activation, covalent functionalization of the charged graphene is achieved by organic diazonium salts. Functionalization was observed spectroscopically, and successfully prevents reaggregation while providing solubility in common organic media.

The era of carbon allotropes.

Twenty-five years on from the discovery of C60, the outstanding properties and potential applications of the synthetic carbon allotropes — fullerenes, nanotubes and graphene — overwhelmingly illustrate their unique scientific and technological importance.

Chemistry with Graphene and Graphene Oxide—Challenges for Synthetic Chemists

The chemical production of graphene as well as its controlled wet chemical modification is a challenge for synthetic chemists. Furthermore, the characterization of reaction products requires sophisticated analytical methods. In this Review we first describe the structure of graphene and graphene oxide and then outline the most important synthetic methods that are used for the production of these carbon-based nanomaterials. We summarize the state-of-the-art for their chemical functionalization by noncovalent and covalent approaches. We put special emphasis on the differentiation of the terms graphite, graphene, graphite oxide, and graphene oxide. An improved fundamental knowledge of the structure and the chemical properties of graphene and graphene oxide is an important prerequisite for the development of practical applications.

Liquid exfoliation of solvent-stabilized few-layer black phosphorus for applications beyond electronics.

Few-layer black phosphorus (BP) is a new two-dimensional material which is of great interest for applications, mainly in electronics. However, its lack of environmental stability severely limits its synthesis and processing. Here we demonstrate that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions in solvents such as N-cyclohexyl-2-pyrrolidone (CHP). Nanosheets are surprisingly stable in CHP, probably due to the solvation shell protecting the nanosheets from reacting with water or oxygen. Experiments, supported by simulations, show reactions to occur only at the nanosheet edge, with the rate and extent of the reaction dependent on the water/oxygen content. We demonstrate that liquid-exfoliated BP nanosheets are potentially useful in a range of applications from ultrafast saturable absorbers to gas sensors to fillers for composite reinforcement.

Wet Chemical Synthesis of Graphene

A suitable technology for the preparation of graphene based on versatile wet chemistry is presented for the first time. The protocol allows the wet chemical synthesis of graphene from a new form of graphene oxide that consists of an intact hexagonal σ-framework of C-atoms. Thus, it can be easily reduced to graphene that is no longer dominated by defects.

PRINCIPLES OF FULLERENE REACTIVITY

The fullerenes have been established as new and versatile building blocks in organic chemistry. A large number of fascinating fullerene derivatives, especially of the icosahedral buck-minsterfullerene C60, have been synthesized. The chemistry of C60 continues to be good for many surprises. However, based on present knowledge a series of reactivity principles can be deduced which makes derivatization of this all carbon cluster more and more predictable. In this article first the geometric and electronic properties of the parent molecule are analyzed. The bent structure of the carbon network C60 and the filling of its molecular orbital with 60 π-electrons dictate the chemical reactivity. A very important aspect that was introduced with the investigation of fullerene chemistry is the shape dependence of reactivity.

A highly water-soluble dendro[60]fullerene

Abstract The nucleophilic cyclopropanation of C60 with a second generation bis(polyamide)-malonate dendrimer and the subsequent deprotection of the terminal t-butyl groups provides a dendro[60]fullerene with 18 carboxylic groups in the periphery. This dendritic monoadduct of C60 is highly water-soluble.

Manipulating single-wall carbon nanotubes by chemical doping and charge transfer with perylene dyes

Single-wall carbon nanotubes (SWNTs) are emerging as materials with much potential in several disciplines, in particular in electronics and photovoltaics. The combination of SWNTs with electron donors or acceptors generates active materials, which can produce electrical energy when irradiated. However, SWNTs are very elusive species when characterization of their metastable states is required. This problem mainly arises because of the polydispersive nature of SWNT samples and the inevitable presence of SWNTs in bundles of different sizes. Here, we report the complete and thorough characterization of an SWNT radical ion-pair state induced by complexation with a perylene dye, which combines excellent electron-accepting and -conducting features with a five-fused ring π-system. At the same time, the perylene dye enables the dispersion of SWNTs by means of π–π interactions, which gives individual SWNTs in solution. This work clears a path towards electronic and optoelectronic devices in which regulated electrical transport properties are important. Using carbon nanotubes in electronic or photovoltaic devices generates active metastable states. These elusive species are hard to characterize because of the polydisperse and aggregate nature of nanotube bundles. A complete characterization of the radical–ion pair state has now been achieved using a range of techniques.