Zois Syrgiannis

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

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.

Reductive retrofunctionalization of single-walled carbon nanotubes.

The chemical functionalization of fullerenes, carbon nanotubes, and graphene is a prerequisite for the use of these synthetic carbon allotropes in high-performance applications. For this reason, addition reactions to the conjugated p system of fullerenes and single-walled carbon nanotubes (SWCNTs) have been intensively investigated. 2] The intrinsic chemical properties of these carbon allotropes can be determined by cage functionalization, but the new derivatives also offer new perspectives such as: 1) increased solubility, processability, and functionality; and 2) properties combined with those of other compound classes. Addition reactions to the sphybridized carbon framework are always accompanied by the generation of sp-hybridized atoms in the cages and, as a consequence, by changes of properties, in particular the electronic structure. This might be considered a drawback because the electronic properties of the parent sp allotropes are in many regards outstanding and unprecedented. However, once the attached addends have completed their assignment in a given process chain, they may be removed such that the structure and function of the SWCNTs are recovered. Cleavage of covalently bound addends, however, often requires high temperatures, conditions that might not be compatible with many applications. In fullerene chemistry mild retrofunctionalization methods have already been discovered such as retro-Diels–Alder reactions and retrocyclopropanations induced by cage reduction with at least two electrons (retro-Bingel reaction, Scheme 1). In the case of the retro-Prato reaction the removal of the pyrrolidine ring from the sp-hybridized carbon sphere is supported by Lewis acid catalysis or microwave irradiation. We have recently developed a very versatile method for the functionalization of the sidewalls of SWCNTs, namely, the nucleophilic addition of metal alkylides and amides followed by reoxidation of the negatively charged intermediates RnSWCNT n to give the neutral derivatives RnSWCNT (Scheme 2). Like the Billups alkylation of carbon nano-

Carbon Nanodots: Supramolecular Electron Donor–Acceptor Hybrids Featuring Perylenediimides

We describe the formation of charge-transfer complexes that feature electron-donating carbon nanodots (CND) and electron-accepting perylenediimides (PDI). The functionalities of PDIs have been selected to complement those of CNDs in terms of electrostatic and π-stacking interactions based on oppositely charged ionic head groups and extended π-systems, respectively. Importantly, the contributions from electrostatic interactions were confirmed in reference experiments, in which stronger interactions were found for PDIs that feature positively rather than negatively charged head groups. The electronic interactions between the components in the ground and excited state were characterized in complementary absorption and fluorescence titration assays that suggest charge-transfer interactions in both states with binding constants on the order of 8×10(4)  M(-1) (25 L g(-1) ). Selective excitation of the two components in ultrafast pump probe experiments gave a 210 ps lived charge-separated state.

Carbon Nanohorns as Integrative Materials for Efficient Dye‐Sensitized Solar Cells

Different nanocarbons, that is, single-wall carbon nanotubes, graphene, single-wall carbon nanohorns (SWCNHs), and their respective oxidized analogs have been used to fabricate novel doped TiO2 electrodes for DSSCs. Our results indicate that all of the nanocarbons significantly enhance the device characteristics when compared to standard TiO2 electrodes. Overall, our most outstanding finding is that SWCNH derivatives are also a plausible material for developing highly-efficient DSSCs.

Modification of Structural and Luminescence Properties of Graphene Quantum Dots by Gamma Irradiation and Their Application in a Photodynamic Therapy

Herein, the ability of gamma irradiation to enhance the photoluminescence properties of graphene quantum dots (GQDs) was investigated. Different doses of γ-irradiation were used on GQDs to examine the way in which their structure and optical properties can be affected. The photoluminescence quantum yield was increased six times for the GQDs irradiated with high doses compared to the nonirradiated material. Both photoluminescence lifetime and values of optical band gap were increased with the dose of applied gamma irradiation. In addition, the exploitation of the gamma-irradiated GQDs as photosensitizers was examined by monitoring the production of singlet oxygen under UV illumination. The main outcome was that the GQDs irradiated at lower doses act as better photoproducers than the ones irradiated at higher doses. These results corroborate that the structural changes caused by gamma irradiation have a direct impact on GQD ability to produce singlet oxygen and their photostability under prolonged UV illumination. This makes low-dose irradiated GQDs promising candidates for photodynamic therapy.

Biocompatible Collagen Paramagnetic Scaffold for Controlled Drug Release.

A porous collagen-based hydrogel scaffold was prepared in the presence of iron oxide nanoparticles (NPs) and was characterized by means of infrared spectroscopy and scanning electron microscopy. The hybrid scaffold was then loaded with fluorescein sodium salt as a model compound. The release of the hydrosoluble species was triggered and accurately controlled by the application of an external magnetic field, as monitored by fluorescence spectroscopy. The biocompatibility of the proposed matrix was also tested by the MTT assay performed on 3T3 cells. Cell viability was only slightly reduced when the cells were incubated in the presence of the collagen-NP hydrogel, compared to controls. The economicity of the chemical protocol used to obtain the paramagnetic scaffolds as well as their biocompatibility and the safety of the external trigger needed to induce the drug release suggest the proposed collagen paramagnetic matrices for a number of applications including tissue engeneering and drug delivery.

An Atom‐Economical Approach to Functionalized Single‐Walled Carbon Nanotubes: Reaction with Disulfides

Owing to their unique structure, thermal stability, and mechanical and electronic properties, single-walled carbon nanotubes (SWCNTs) have been a subject of continuous and intense interest. However, various applications in many fields, such as molecular electronics, solar cells, and nanomedicine, often require the development of reproducible protocols for the chemical modification of SWCNTs. In fact, one of the main drawbacks of the use of SWCNTs is their tendency to aggregate and intrinsic poor solubility, which prevent their manipulation and limit their potential. To date, several methods have been described for the chemical functionalization of SWCNTs; however, new versatile and reliable methods are still needed.We focused our attention on disulfides, which are a very useful family of compounds owing to the presence of the flexible S S bond. Disulfides can be prepared readily from the corresponding thiols; thus, a wide range of substrates are accessible. In this study, we used very mild and reproducible conditions for the production of a wide variety of functionalized SWCNTs (f-SWCNT). Pristine HiPco SWCNTs (p-SWCNTs, prepared with high-pressure carbon monoxide, HiPco) were treated with disulfides in deoxygenated toluene at reflux (Scheme 1). The reaction with diphenyl disulfide was monitored for 48 h by

The supramolecular design of low-dimensional carbon nano-hybrids encoding a polyoxometalate-bis-pyrene tweezer

A novel bis-pyrene tweezer anchored on a rigid polyoxometalate scaffold fosters a unique interplay of hydrophobic and electrostatic supramolecular interactions, to shape carbon nanostructures (CNSs)-based extended architectures.

Electronic Properties of Propylamine‐Functionalized Single‐Walled Carbon Nanotubes

We present resonant Raman measurements on single-walled carbon nanotubes (SWCNT) functionalized with propylamine groups at different degrees. Direct nucleophilic addition based on in situ generated primary amides is used for attaching n-propylamine to the sidewalls of SWCNTs. The influence of the amino functionalities on the electronic structure of the nanotubes is investigated. From the Raman resonance profiles of the radial breathing modes (RBMs), the chiral indices of the corresponding tubes are assigned. We observe significant redshifts of the transition energies and a broadening of the resonance windows due to chemical modification of SWCNTs. Similar redshifts are derived from the analysis of the NIR/Vis transmission spectrum. The relative Raman intensities of the functionalized samples and the evaluation of their transmission spectra indicate a diameter dependence of the reactivity as it has been observed for other moieties. By analyzing the defect induced D mode we observe a considerable degree of functionalization accompanied by an almost unharmed tube structure, which ensures that the observed effects are mainly driven by changes of the electronic structure.

On Demand Release of Hydrosoluble Drugs From a Paramagnetic Porous Collagen‐Based Scaffold

The design of a collagen scaffold containing iron oxide nanostructures capped by a TiO2 (anatase) layer is reported. The TiO2 shell is proposed to perform a dual role: 1) as an innovative and biocompatible cross-linker agent, providing binding sites to the protein moiety, through the well-known TiO2 chemical affinity towards carboxyl groups, and 2) as a protective surface layer for the paramagnetic core against oxidation. Simultaneously, the presence of the nanostructures confers to the collagen gel sensitivity to an external stimulus; that is, the application of a magnetic field. The hybrid biomaterial was demonstrated to be nontoxic and is proposed as a smart scaffold for the release of bioactive compounds on demand. The tuneable release of a model protein (myoglobin) upon application of a magnetic field was investigated. Myoglobin was loaded in the microporous material and discharge was induced by consecutive magnet applications, leading to release of the protein with high spatio-temporal and dosage control.