Photoactive ruthenium complexes

Ruthenium complexes can be employed as photosensitizers in several ways  

Attachment of Ruthenium Complex to Enzyme Substrate or Ligand 

The strategy based on the attachment of the photosensitizer via an aliphatic spacer 

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In a second variant, growth of metallodendrimers can proceed via complexa-tion of a metal cation with dendritic ligands. In this way, Balzani, Vogtle, De Cola et al. [34] obtained photoactive ruthenium complexes by spontaneous self-assembly of the components starting from various dendritically substituted bi-pyridines. Fig. 2.9 shows a representative example (see Sections 5.1.2.3 and... 

Millett F, Durham B. Design of photoactive ruthenium complexes to study interprotein electron transfer. Biochemistry 2002 41 11315-24. 

Figure 5.61 Schematic representation of a [Ru(bpy)3]2+/a-ZrP viologen structure on silica, plus the sequence of fast (1,2) and slow (3) electron transfer steps that follow photoexcitation of the photoactive ruthenium-containing polymer MDESA, p-methoxyaniline diethylsulfonate. Reprinted from Coord. Chem. Rev., 185-186, D. M. Kaschak, S. A. Johnson, C. C. Waraksa, J. Pogue and T. E. Mallouk, Artificial photosynthesis in lamellar assemblies of metal poly(pyridyl) complexes and metalloporphyrins, 403-416, Copyright (1999), with permission from Elsevier Science...

To get inside the oxidative damage of DNA caused by photoactive ruthenium(II) intercalators, complexes can be attached to one end of double-stranded DNA. The great advantage of this method is that intercalation of tethered metal complexes takes place at a defined distance from the oxidation site. The ruthenium(II) complex of the type [Ru(bpy )(Me2dppz)(phen)]2+ (structure of ligands presented in Figure... 

Cyclic water cleavage by visible light was also achieved in electron relay free systems (48). In this case the fraction of sensitizer that Is absorbed onto the particle surface is photoactive and electron injection occurs directly from its excited state into the Ti02 conduction band. Using the surfactant ruthenium complex depicted in Figure 10, a quantum yield of 7% was obtained for the water splitting process. 

Other species. In a study by the Che group, it proved possible to prepare a composite complex that spans both categories. Thus, oxidation (either chemical or electrochemical) of the double-helical [Ru2L2(H20)2] (L = quinquepyridine) cation in aqueous solution results in a product containing both a photoactive ruthenium centre and a high-valent Ru=0 centre in the one complex. 

A photoactive metal center is introduced in these systems. The ruthenium bipyridyl complexes are coordinated to the emeraldine base to form the corresponding polymer complexes as described above." The incorporation of the ruthenium centers to the pyridyl backbone has been also reported to give the ruthenium complexes Conjugated ruthenium bipyridine complexes thus obtained are evaluated to be photorefractive materials. Other transition metal complexes can be employed to form the corresponding polymer complexes. The pyridine unit is replaced by bithienyl, 1,4-diazabutadiene, ethylene, benzimidazole or thiazole. ... 

The ligand Antpy is readily prepared (Figure 2), and consists of a tridentate tpy metalbinding domain to which a photoactive anthryl group is covalently attached [6]. The ligand shows a K-K absorption at 253 nm. The ruthenium complex [Ru(Antpy)2]2+ is readily... 

The X-ray structure of zinc naphthalocyanate has been determined with Zn—N bond lengths of 1.983(4) A.829 Pentanuclear complexes with a zinc phthalocyanine core and four ruthenium subunits linked via a terpyridyl ligand demonstrate interaction between the photoactive and the redox active components of the molecule. The absorbance and fluorescence spectra showed considerable variation with the ruthenium subunits in place.830 Tetra-t-butylphthalocyaninato zinc coordinated by nitroxide radicals form excited-state phthalocyanine complexes and have been studied by time-resolved electron paramagnetic resonance.831... 

The long lifetimes and high redox potentials of a range of ruthenium(II) complexes and in particular [Ru(bpy)3] " have important consequences for their use as photoactive redox catalysts. This area of research is extremely active and we now focus on the decay of the excited state of [Ru(bpy)3] + ( [Ru(bpy)3] " ) and its quenching. Braterman et al. have described the electronic absorption spectrum and structure of the emitting state of [Ru(bpy3] +, and the effects of excited state asymmetry. The effects of solvent on the absorption spectrum of [Ru(bpy)3] " have been studied. In H2O, MeCN and mixtures of these solvents, the value of e(450 nm) remains the same ((4.6 0.4) x 10 dm mol cm ). The ground state spectrum is essentially independent of... 

Polymetallic complexes presenting directional energy migration are of much significance for the design of photochemical molecular devices. Large arrays of multiple photoactive and redox-active building blocks (of ruthenium- or osmium tris(bipyri-dine)-type for instance) have been constructed for such purposes [A. 10,8.25-8.27]. 

Dyads and triads based on the photoactive, multibridging [Ru(bpz)3] (bpz = bipyrazine) complex directly bound to transition metal complexes were obtained by following the procedures previously reported for the generation of symmetric heptanuclear supermolecules (67-69). Such systems contain a tris(bpz)ruthenium (II) ion [RuJ attached to bis(bpy)chlororuthenium(II)/(III) [Rup], or penta-cyanoferrate(II)/(III) complexes via a bpz bridging ligand, as shown for the... 

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