Controlling the Direction of the Molecular Axis of Rod-Shaped Binuclear Ruthenium Complexes on Single-Walled Carbon Nanotubes

Hydrogen-bonded metallo-supramolecular polymers based on ruthenium or iron complexes for the selective extraction of single-walled carbon nanotubes

The chemical functionalization of nano-carbon materials such as single-walled carbon nanotubes (SWNTs) and graphene by metal complexes has attracted much attention due to the multitude of potential applications in efficient energy-conversion and -storage devices. The solubilization and single-chirality separation of SWNTs by surface modifications is a useful approach to manipulate SWNTs in the liquid phase. In this study, several Ru and Fe complexes containing two terminal quadruple hydrogen-bonded (H-bonded) ureidopyrimidinedione (UPy) groups were synthesized (Ru-1, Ru-UPy, and Fe-UPy) to form H-bonded supramolecular polymers by self-association. In order to control the solubility of these complexes in nonpolar solvents, Ru-UPy and Fe-UPy were endowed with long alkyl side chain groups in the coordinated 2,6-bis(benzimidazol-2-yl)pyridine ligand, while Ru-1 and Ru-2 do not contain such long alkyl chain groups. AFM measurements revealed that Ru-1, Ru-UPy, and Fe-UPy form a fiber-like network morphology on HOPG surfaces, arising from the H-bonded aggregation. However, only Ru-UPy and Fe-UPy are able to solubilize SWNTs effectively upon simple sonication in chlorobenzene. After the solubilization of a CoMoCAT® SWNT in chlorobenzene using Ru-UPy or Fe-UPy, UV-Vis-NIR spectra showed sharp peaks at 996 and 1150 nm, which were attributed to (6, 5) and (7, 6)-SWNTs. The Raman spectra of the solubilized SWNTs revealed peaks that were attributed to the radial breathing mode (RBM), which suggests an enrichment of semiconducting SWNTs, i.e., Ru-UPy and Fe-UPy are able to selectively solubilize semiconducting SWNTs. Cyclic voltammograms of films of SWNTs covered with Ru-UPy or Fe-UPy on ITO electrodes showed a well-defined adsorbed Ru(ii/iii) or Fe(ii/iii) wave. Upon addition of acid, the redox response from the adsorbed H-bonded Ru-UPy and Fe-UPy disappeared and only SWNTs were left on the ITO electrode. Moreover, the Ru-UPy/SWNT and Fe-UPy/SWNT hybrids exhibited non-linear I-V characteristics.

Heptamethine Cyanine Dyes in the Design of Photoactive Carbon Nanomaterials

Near-infrared (NIR) absorbing nanomaterials, built from anionic heptamethine cyanine dyes and single-walled carbon nanotubes or few-layer graphene, are presented. The covalent linkage, using 1,3-dipolar cycloaddition reactions, results in nanoconjugates that synchronize the properties of both materials, as demonstrated by an in-depth characterization study carried out by transmission electron microscopy, atomic force microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. UV-vis-NIR and Raman spectroscopies further confirmed the unique electronic structure of the novel photoactive nanomaterials.

Controlling the Molecular Direction of Dinuclear Ruthenium Complexes on HOPG Surface through Noncovalent Bonding

We synthesized three types of binuclear Ru complexes (1-3) that contain pyrene anchors for the adsorption of 1-3 onto nanocarbon materials via noncovalent π-π interactions, in order to investigate their adsorption onto and their desorption from highly ordered pyrolytic graphite (HOPG). The adsorption saturation for 1 (6.22 pmol/cm²), 2 (2.83 pmol/cm²), and 3 (3.53 pmol/cm²) on HOPG was obtained from Langmuir isotherms. The desorption rate from HOPG electrodes decreased in the order 3 (2.4 × 10^-5 s^-1) > 2 (1.4 × 10^-5 s^-1) ≫ 1 (1.8 × 10^-6 s^-1). These results indicate that the number of pyrene anchors and their position of substitution in such complexes strongly affect the desorption behavior. However, neither the free energy of adsorption (ΔG_ads) nor the heterogeneous electron-transfer rate (k_ET) showed any significant differences among 1-3, albeit that the surface morphologies of the modified HOPG substrates showed domain structures that were characteristic for each Ru complex. In the case of 3, the average height changed from ∼2 to ∼4 nm upon increasing the concentration of the solution of 3 that was used for the surface modification. In contrast, the height for 1 and 2 remained constant (1.5-2 nm) upon increasing the concentration of the complexes in the corresponding solutions. While the molecular orientation of the Ru-Ru axis of 3 relative to the HOPG surface normal changed from parallel to perpendicular, the Ru-Ru axis in 1 and 2 remained parallel, which leads to an increased stability of 1 and 2.