Two‐Photon Chemistry in Ruthenium 2,2′‐Bipyridyl‐Functionalized Single‐Wall Carbon Nanotubes

Abstract

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.

Visible‐Light Photocatalytic Hydrogen Generation by Using Dye‐Sensitized Graphene Oxide as a Photocatalyst

“…This could be due to triplet–triplet annihilation or some other kind of self‐quenching that competes with the required electron transfer from the [Ru(bipy) 3 ] 2+ triplet excited state to GO1. In previous studies of [Ru(bipy) 3 ] 2+ covalently attached to single‐wall carbon nanotubes, we have observed, by using laser flash photolysis, a clear change in the nature of the transients depending on the concentration of [Ru(bipy) 3 ] 2+ 16. Moreover, recently we have determined two different regimes in the quenching of [Ru(bipy) 3 ] 2+ triplets by G in aqueous solution 17…”

Coordination chemistry on carbon surfaces

“…Moghadam [382] followed by the coordination of the metal center with the pendant N-, O-or S-group (Table 25, entries 1-8). Garcia et al prepared thiol-functionalized SWCNT through an amidation of the COClmodified support with 2-aminoethanethiol as a chemical linker (Table 25, entry 9) [421]. Then, they immobilized a Ru complex onto this material through a radical addition between the thiolfunctionalized support and a terminal C C double bond present on the ruthenium complex.…”

Photochemical Evidence of Electronic Interwall Communication in Double‐Wall Carbon Nanotubes

“…Scheme summarizes our proposal. In a related precedent, it has been observed that the photoinduced disproportionation of tris(2,2′‐bipyridyl)ruthenium(II) to the corresponding +1 and +3 oxidation states takes only place when this metal complex is bonded to CNT walls (and not in concentrated solutions) and is promoted by the high mobility of electrons in CNT due to the graphenic walls 39. Our proposal to rationalize the role of the integral, inner wall as charge recombination center is analogous to the current paradigm in photocatalysts containing noble metal nanoparticles in which a large percentage of these conductive metal particles on the surface increases charge recombination by acting as recombination centers 40…”