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Two‐Photon Chemistry in Ruthenium 2,2′‐Bipyridyl‐Functionalized Single‐Wall Carbon Nanotubes
Author(s) -
Martín Roberto,
Jiménez Liliana,
Alvaro Mercedes,
Scaiano Juan C.,
Garcia Hermenegildo
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200903506
Subject(s) - ruthenium , photochemistry , carbon nanotube , disproportionation , materials science , chemistry , spectroscopy , absorption spectroscopy , nanotechnology , organic chemistry , catalysis , physics , quantum mechanics
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 CC double bond of a bipyridyl ligand of the ruthenium tris(bipyridyl) complex. The resulting macromolecular Ru‐SWCNT (≈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.