Ruthenium-complex excited state, rapid

Based on extensive screening of hundreds of ruthenium complexes, it was discovered that the sensitizer s excited state oxidation potential should be negative of at least —0.9 V vs. SCE, in order to inject electrons efficiently into the Ti02 conduction band. The ground state oxidation potential should be about 0.5 V vs. SCE, in order to be regenerated rapidly via electron donation from the electrolyte (iodide/triiodide redox system) or a hole conductor. A significant decrease in electron injection efficiencies will occur if the excited and ground state redox potentials are lower than these values. 

Upon excitation of the metal complex centre, triplet energy transfer to the donor appended porphyrin rapidly quenches the excited state of the central ruthenium bis-terpyridyl unit, whereas excitation of the gold porphyrin, leads in less than 1 ps to the triplet-excited state [23], which is unreactive to-... 

Quenching of the ( CT)[Ru(bipy)3] by [Cr(bipy)]3 has been studied. This is via electron transfer to the Cr complex and a rapid back reaction. The ruthenium complex will also quench the 727 nm emission of the metal-centred doublet excited state of the chromium species, by a similar mechanism. Evidently both ligand- and metal-centred excited states can be quenched by bimolecular redox processes. A number of Ru complexes, e.g. [Ru(bipy)3] and [Ru(phen)3] also have their luminescence quenched by electron transfer to Fe or paraquat. Both the initial quenching reactions and back reactions are close to the diffusion-controlled limit. These mechanisms involve initial oxidation of Ru to Ru [equation (1)]. However, the triplet excited state is more active than the ground state towards reductants as well as... 

Tris (2,2 -bipyridyl)ruthenium(II) has been used as the basis of CL detection of a wide range of compounds after oxidation to the ruthenium(III) complex. The analyte interacts with the ruthenium(III) complex reducing it to the ruthenium(II) complex in an excited state, which then emits CL as it returns to the ground state. In the present study, a flow injection procedure for SPAX determination with CL detection was proposed in which ruthenium(II) was oxidized by Ce(IV) solution. The CL emission intensity depended on the concentration of the analyte in the CL system. This work describes a relatively sensitive and rapid chemiluminescence method for SPAX determination based on tris(2,2 -bipyridyl)ruthenium(II) without sample pretreatment process. 

Modification of larger proteins with ruthenium complexes, while possible, have proven difficult. Fortunately, a ruthenium labeled partner such as Cc can be used to rapidly inject or remove an electron from the large protein complex, and thus study internal electron-transfer reactions. In a complementary approach, Nilsson found that the excited state of Ru(bpy)3 + can inject an electron into CcO. The ruthenium complex binds electrostatically to the protein in a location similar to that occupied by Cc. The initial site of electron transfer is the Cua site, as it is when Cc is the electron donor. The simplicity of this technique makes it very attractive since it eliminates any modification of the protein which might alter the structure. Sadoski etal. showed that significant improvements in the yield of electron transfer could be obtained with ruthenium complexes of higher charge. One specific complex used was the dinuclear complex [(bpy)2Ru(qpy)Ru(bpy)2] + (Figure 10). ... 

In fluid solutions, the resolvation times can be in the subnanosecond time regime. For example, the rapid (<100 ps) relaxation of the excited-state absorption spectra of ruthenium polypyridyl complexes following metal-to-ligand charge-transfer (MLCT) excitation in aqueous solutions have been ascribed to diffusional resolvation of the MLCT excited state. Finally, Robinson and co-workers have provided evidence that the rate of ionization of the singlet excited state of 6-p-toluidine-2-naphthalenesulfonate is determined by the rate at which neighboring solvent fluctuations can form a 3-4 water molecule cluster capable of solvating the electron. 

Of particular interest at present is the development of complexes for dye-sensitized solar cells (Section 3.8.3). The role of the transition-metal complex is in optical absorption, and the electrons are then passed from the excited state to the conduction band of a wide-band-gap semiconductor. The preferred complexes involve octahedrally coordinated ruthenium with bipyridyl ligands, for which the optical transition involves an MLCT transition of an electron from the metal to an antibonding orbital of the bipyridyl ligand, from where it is very rapidly transferred to the conduction band of Ti02. 

Photolysis of a solution containing [Ru(bipy)3] +, [Ru(phen)3] +, and [Fe(H20)s] + gives the excited states of both ruthenium(ii) complexes, which are then rapidly oxidized by Fe + to the corresponding ruthenium(iii) complexes. With suitable initial concentration, this generates the four components of equation (113) in a non-equilibrium ratio the system then returns to equilibrium at a measurable rate, followed by the slower reactions of [Ru(phen)a] + and [Ru(bipy)3] + with Fe - -. Non-complementary Reactions. (Table 5)—The reaction [PtClgl + Cu in chloride media obeys the rate law (98), implying that platinum(iii) is formed as a short-lived intermediate in equilibrium with the reactants [equations (96) and (97)], and... 

In Harriman and coworkers dyad [143], the ZnTPP and Ru(bpy)j are covalently linked by a Pt" bis-a-acetyfide. When the dyad is irradiated at 390 nm in acetonitrile, the excited singlet Sj state of the zinc porphyrin undergoes rapid energy transfer to Ru(bpy)3, generating the MLCT excited singlet state of the ruthenium complex. 

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