Evidence for iodine atoms as intermediates in the dye sensitized formation of I-I bonds.

Visible light excitation of [Ru(bpz)(2)(deeb)](PF(6))(2), where bpz is 2,2'-bipyrazine and deeb is 4,4'-(CO(2)Et)(2)-2,2'-bipyridine, in acetonitrile solutions with iodide is shown to initiate excited-state electron transfer reactions that yield iodine atoms. The iodine atoms subsequently react with iodide to form the I-I bond in I(2)(-*). The resultant Ru(bpz(-))(bpz)(deeb)(+), I(2)(-*) stores approximately 1.64 eV of free energy and returns cleanly to ground-state products with k(cr) = (2.1 +/- 0.3) x 10(10) M(-1) s(-1).

Large footprint pyrene chromophores anchored to planar and colloidal metal oxide thin films.

Sensitization and binding of a large footprint pyrene chromophore to planar (sapphire) and colloidal metal oxide films (TiO2 and ZrO2) is investigated. The model compound combines a 1-pyrenyl-ethynylenephenylene unit with a new adamantane-tripodal linker that binds to the surface. The linker design, combining a large footprint (approximately 2 nm2) of the tripodal linker with the meta position of the COOH anchoring groups, was suggested from atomistic models, and it aims to provide improved spacing control. The pyrene chromophore unit provides a probe of sensitizer-sensitizer interactions through its propensity to form excimers, unless neighboring pyrene units are sufficiently spaced (>or=3.5 A). Absorption and fluorescence studies, and a comparison with a pyrene-rigid rod model compound, suggest that the new tripodal anchor group allows spacing control on planar surfaces. On colloidal films, the linker provides spacing control at low surface coverage but sensitizer-sensitizer interactions are still observed on colloidal films at high surface coverage. Implications for the functionalization of metal oxide films in hybrid molecule-metal oxide semiconductor material systems are discussed.