Ruthenium photoactive

Meisel etal. [18-20] were the first to investigate how the addition of a polyelectrolyte affects photoinduced ET reactions. They found that charge separation was enhanced as a result of the retardation of the back ET when poly(vinyl sulfate) was added to an aqueous reaction system consisting of tris(2,2 -bipyridine)ruthenium(II) chloride (cationic photoactive chromophore) and neutral electron acceptors [21]. More recently, Sassoon and Rabani [22] observed that the addition of polybrene (a polycation) had a significant effect on separating the photoinduced ET products in an aqueous solution containing cir-dicyano-bis(2,2 -bipyridine)ruthenium(II) (photoactive donor) and potassium hexacyano-ferrate(III) (acceptor). These findings are ascribable to the electrostatic potential of the added polyelectrolytes. 

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]. 

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... 

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...

When the interfacial supramolecular triad is irradiated in the presence of I- under solar cells conditions, appreciable photocurrents are obtained. The profile of the photoaction spectrum shows clearly that photoinjection into TiC>2 takes place upon excitation of the ruthenium center. However, the IPCE values obtained are lower than those observed for the model compound, thus suggesting that injection is less efficient in the heterotriad. Of major interest is the mechanism for charge injection. Two different pathways can be envisaged. First, the charge injection may be a two-step process and takes place via the rhodium center as shown in the following equations ... 

In a more general sense, these observations show that upon immobilization of photoactive compounds onto a solid substrate a substantial difference is detected between the photophysical processes observed for the heterotriad and the dyad in solution. More importantly, direct injection from those moieties not directly bound to the oxide surface can be efficient - this is always fully realized and such an observation is important for the further development of real devices. As a result of this through-space interaction, no osmium-based emission is observed and injection from both the ruthenium and the osmium centers is faster than the laser pulse. An interesting observation is also that upon irradiation of the heterotriad Ti02-Ru-0s, only one final product, i.e. Ti02(e)-Ru(ll)0s(lll), is obtained. In view of the potential of these modified surfaces as potential molecular devices, this is an important feature. The presence of a rigid structure rather than a flexible one, as observed in the Ru-Rh case, clearly leads to a more uniform behavior. 

Perylenediimides represent another class of photoactive dyes which are characterized by their strong fluorescence emission and facile electrochemical reduction. Recently, a supramolecular bis(phthalocyanine)-perylenediimide hetero-triad (compound 42) has been assembled through axial coordination [47]. Treatment of perylenediimide 43, which has two 4-pyridyl substituents at the imido positions, with 2.5 equiv. of ruthenium(II) phthalocyanine 44 in chloroform affords 42 in 68% yield (Scheme 3). This array shows remarkable stability in solution due to the robustness of the ruthenium-pyridyl bond. Its electronic absorption spectrum is essentially the sum of the spectra of its molecular components 43 and 44 in... 

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

Hamachi I, Tanaka S,Tsukiji S, Shinkai S, Oishi S. Design and semisynthesis of photoactive myoglobin bearing ruthenium tris(2,2 -bipyridine) using cofactor-reconstitution. Inorg Chem 1998 37 4380-8. 

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. 

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... 

The photoaction spectrum of a cell assembled with the ruthenium cluster dye is shown in Fig. 66 (right). A photocurrent maximum is observed at 350nm. It... 

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