Functional macromolecules from single-walled carbon nanotubes: synthesis and photophysical properties of short single-walled carbon nanotubes functionalised with 9,10-diphenylanthracene

Two-photon chemistry in ruthenium 2,2'-bipyridyl-functionalized single-wall carbon nanotubes

Ruthenium polypyridyl complexes are widely used as light harvesters in dye-sensitized solar cells. Since one of the potential applications of single-wall carbon nanotubes (SWCNTs) and their derived materials is their use as active components in organic and hybrid solar cells, the study of the photochemistry of SWCNTs with tethered ruthenium polypyridyl complexes is important. A water-soluble ruthenium tris(bipyridyl) complex linked through peptidic bonds to SWCNTs (Ru-SWCNTs) was prepared by radical addition of thiol-terminated SWCNT to a terminal C=C double bond of a bipyridyl ligand of the ruthenium tris(bipyridyl) complex. The resulting macromolecular Ru-SWCNT (approximately 500 nm, 15.6% ruthenium complex content) was water-soluble and was characterized by using TEM, thermogravimetric analysis, chemical analysis, and optical spectroscopy. The emission of Ru-SWCNT is 1.6 times weaker than that of a mixture of [Ru(bpy)(3)](2+) and SWCNT of similar concentration. Time-resolved absorption optical spectroscopy allows the detection of the [Ru(bpy)(3)](2+)-excited triplet and [Ru(bpy)(3)](+). The laser flash studies reveal that Ru-SWCNT exhibits an unprecedented two-photon process that is enabled by the semiconducting properties of the SWCNT. Thus, the effect of the excitation wavelength and laser power on the transient spectra indicate that upon excitation of two [Ru(bpy)(3)](2+) complexes of Ru-SWCNT, a disproportionation process occurs leading to delayed formation of [Ru(bpy)(3)](+) and the performance of the SWCNT as a semiconductor. This two-photon delayed [Ru(bpy)(3)](+) generation is not observed in the photolysis of [Ru(bpy)(3)](3+); SWCNT acts as an electron wire or electron relay in the disproportionation of two [Ru(bpy)(3)](2+) triplets in a process that illustrates that the SWCNT plays a key role in the process. We propose a mechanism for this two-photon disproportionation compatible with i) the need for high laser flux, ii) the long lifetime of the [Ru(bpy)(3)](2+) triplets, iii) the semiconducting properties of the SWNT, and iv) the energy of the HOMO/LUMO levels involved.

Photoinduced formation and characterization of electron-hole pairs in azaxanthylium-derivatized short single-walled carbon nanotubes

2-Azaxanthone, a nitrogenated derivative of the well-studied organic chromophore xanthone, has been covalently bound through 2-(ethylthio)ethylamido linkers to the carboxylic acid groups of short, soluble single-walled carbon nanotubes (CNTs) of 450 nm average length, and the resulting azaxanthylium-functionalized CNTs (AZX-CNT, 8.5 wt % AZX content) characterized by solution (1)H NMR, Raman and IR spectroscopy and thermogravimetric analysis. Comparison of the quenching of the triplet excited state of AZX (steady-state and time-resolved) and of the transient optical spectra of CNTs and AZX-CNT shows that the covalent linkage boosts the interaction between the azaxanthylium moiety and the short CNT units. The triplet excited state of the azaxanthylium derivative is quenched by CNT with and without covalent bonding, but when it is covalently bonded, the singular transient spectrum is compatible with the photogeneration of electron holes through electron transfer from CNT to excited azaxanthylium units.

The electrochemical signature of functionalized single-walled carbon nanotubes bearing electroactive groups

We report the modification and characterization of single-walled carbon nanotubes (SWCNTs) in view of molecular sensing applications. We found that ultrasonicated SWCNTs present sticking properties that make them adhere on electrode surfaces. This allows excellent characterization of SWCNTs by cyclic voltammetry (CV) before and after chemical functionalization with diazonium salts bearing electroactive groups. Bare SWCNTs presented distinct invariant shapes in CV, used as control curves, in comparison with functionalized SWCNTs for which specific signatures corresponding to the presence of grafted molecules were identified. According to the electronic substituents in the para position of the diazonium salts, divergent behaviours were observed for the grafting reactions. Diazonium salts having electrowithdrawing groups could be grafted without electrochemical induction whereas those bearing electron donating groups required a cathodic potential to generate the formation of the radical species.

Single-walled carbon nanotubes decorated with a pyrene-fluorenevinylene conjugate

Single-walled carbon nanotubes are noncovalently functionalized using a pyrene-fluorenevinylene dye and the resulting nanohybrids are isolated from the free molecules. The tubes modified by means of this noncovalent approach show enhanced solubility in organic media. The structure and morphology of this hybrid material are fully characterized using absorption, infrared and Raman spectroscopies as well as atomic force and scanning electron microscopies. Steady state fluorescence measurements reveal that significant quenching of the pyrene derivative excited state takes place through an energy transfer mechanism.