Carbon Nanotube Sidewall Functionalization with Carbonyl Compounds—Modified Birch Conditions vs the Organometallic Reduction Approach

Abstract

Covalent addition reactions turned out to be one of the most important functionalization techniques for a structural alteration of single walled carbon nanotube (SWCNT) scaffolds. During the last years, several reaction sequences based on an electrophilic interception of intermediately generated SWCNT(n-) carbanions, obtained via Birch reduction or by a nucleophilic addition of organometallic species, have been developed. Nevertheless, the scope and the variety of potential electrophiles is limited due to the harsh reaction conditions requested for a covalent attachment of the functional entities onto the SWCNT framework. Herein, we present a significant modification of the reductive alkylation/arylation sequence, the so-called Billups reaction, which extends the portfolio of electrophiles for covalent sidewall functionalization to carbonyl compounds--ketones, esters, and even carboxylic acid chlorides. Moreover, these carbonyl-based electrophiles can also be used as secondary functionalization reagents for anionic SWCNT intermediates, derived from a primary nucleophilic addition step. This directly leads to the generation of mixed functional SWCNT architectures, equipped with hydroxyl or carbonyl anchor groups, suitable for ongoing derivatization reactions. A correlated absorption and emission spectroscopic study elucidates the influence of the covalent sidewall functionalization degree onto the excitonic transition features of carbon nanotubes. The characterization of the different SWCNT adducts has been carried out by means of Raman, UV-vis/nIR, and fluorescence spectroscopy as well as by thermogravimetric analysis combined with mass spectrometry and X-ray photoelectron spectroscopy analysis.

Electroactive carbon nanoforms: a comparative study via sequential arylation and click chemistry reactions

“…Notably, this Unfortunately, the lower degree of functionalization achieved in MWCNT and graphene samples do not allowed a proper photophysical characterization of the aggregates formed. As a matter of fact, following photoexcitation at 387 nm, the 30 differential absorption spectra of GR-2 are like those seen for the starting material, that is, exfoliated graphite ( Figure S17). In the visible, we note an ultrashort lived transient -in the form of bleaching -between 550 and 800 nm.…”

“…27 An analogous behavior was observed for SWCNT-2 and GR-2 ( Figures S10 and S11). The absence of the peak corresponding to the free azide groups at 405.0 eV 30 unambiguously proves that the azido exTTF is covalently attached to the carbon nanomaterials rather than beeing simply physisorbed onto the surface by π-stacking interactions. 28 A single S 2p signal at around 170 eV was found for the samples subjected to the click reaction, indicating the presence of sulfur To complement the characterization of the nanoconjugates, TEM investigations were employed to study their morphology.…”

“…2 Likewise, the appealing features of fullerenes 3 and carbon nanotubes (CNT) 4 also make them attractive building blocks for the aforementioned applications. 30 Two major drawbacks hamper, however, the application of CNT and graphene for practical purposes, namely their lack of solubility in common solvents and their relative inert surfaces. To overcome such setbacks, both covalent and non-covalent chemical modifications have been investigated in recent years.…”

“…Graphene samples excited at 532 nm reveal the typical Raman peaks of exfoliated graphite, namely, the D-, G-, and 2D-bands 30 centered around 1340, 1565, and 2678 cm -1 , respectively. Upon exfoliation, a slight increase in the D band intensity is noticed due to defects induced by the ultrasonication process.…”

Synthesis and electrochemical applications of nitrogen-doped carbon nanomaterials

“…The carboxylic acid groups are considered as one of the best choices because they can undergo a variety of reactions for further modification and are easily formed via the various oxidizing treatments, e.g., sonication in sulfuric and nitric acid, refluxing in nitric acid, ozonolysis, and air. The carboxyl-functionalized CNT can be further grafted ( Figure 4) by the functional moieties with the terminal amine oxidization including the different mechanisms from the defect site chemistry oxidation reactions, esterification/amidation reactions to the oxidized CNTs [88,89], nucleophilic additions/electrophilic additions [85,90], mechanochemical functionalization [91,92], cycloaddition reactions, ionic liquids (ILs) [93,94], electrochemical modifications, diazotization [95], and radical additions [96]. The CNT functionalization via amidation and esterification of the nanotubebound carboxylic acids [97], poly(benzyl ether) [62], and poly(amido-amine) (PAMAM) dendrons results in the dendrimer-MWCNTs hybrid materials of two enzymes, porcine pancreas lipase (PPL) and aminolipase (AL).…”