Charge transfer excited state of Ru

Polypyridine rhodium(III) complexes (RM ) may be reduced by one-electron reductants The reductants which have been successfully employed include Ru(bpy)32+, the luminescent charge-transfer excited state of Ru(bpy)32+ (J, 9)... 

We have reported the first direct observation of the vibrational spectrum of an electronically excited state of a metal complex in solution (40). The excited state observed was the emissive and photochemically active metal-to-ligand charge transfer (MLCT) state of Ru(bpy)g+, the vibrational spectrum of which was acquired by time-resolved resonance Raman (TR ) spectroscopy. This study and others (19,41,42) demonstrates the enormous, virtually unique utility of TR in structural elucidation of electronically excited states in solution. 2+... 

The reductant is the charge-transfer excited state of the Ru(II) complex. 

The photoreduction of viologens in surfactant systems has also been described by Massini and Voorn [70]. An amphipathic derivative of methyl viologen (Ci4MV ) (XII) has been employed as an electron acceptor in reactions involving the charge-transfer excited state of the ruthenium complex Ru(bpy) the reaction products MV and Ru(bpy)3 of the reaction between and... 

Figure 2. Schematic representation of some relevant ground and excited-state properties of Ru(bpy)j. MLCT and MLCT are the spin-allowed and spin-forbidden metal-to-ligand charge transfer excited states, responsible for the high intensity absorption band with = 450 nm and the luminescence band with = 615 nm, respectively. The other quantities shown are intersystem crossing efficiency energy (E°°) and lifetime (x) of the MLCT state luminescence quantum yield ( ) quantum yield for ligand detachment (O,). The reduction potentials of couples involving the ground and the MLCT excited states are also indicated.

With the exception of a few highly studied states, such as, for example, the redox active lowest metal-to-ligand charge transfer excited state (MLCT) in the [Ru(bipyridine)3]2t cation, or the ligand field active 2E state of Cr(IlI), we know relatively little about these excited states. An enormous body of knowledge is waiting to be explored. 

The fundamentals of electron transfer from an adsorbed molecule to a solid substrate has been considered by Willig and co-workers [9]. In this study, the photoinduced electron injection from the excited state of [Ru(dcbpy)2(NCS)2] into nanocrystalline TiC>2 was investigated both in high vacuum and in methanol containing 0.3 M LiCl. The central issue addressed in this investigation was to determine the time-scale on which the photoinduced electron injection from the molecular component to the solid substrate occurs. Transient absorption spectroscopy was used to follow this charge separation. The measurement was based on... 

Influence of Field Effect. Since electron transfer rates are directly related to the field, a judicious manipulation of the distance of a sensitizer and an electron acceptor (or donor) from a highly charged surface across the Stem layer (Figure 2, equation 7) is expected to result in altered efficiencies. This expectation has been realized In achieving effective charge separation under the Influence of a positive electric field, generated by DODAC vesicles (35). Rate constant for electron transfer from L-cystelne to the excited state of Ru(bpy) ... 

A great deal of work on Ru-modified proteins has employed the Ru(bpy)2(im) (HisX) " (bpy = 2,2 -bipyridine im = imidazole) label [16, 21, 26] (Figure 2). In addition to favorable ET properties, these Ru-bpy complexes have long-lived, luminescent metal-to-ligand charge-transfer excited states that can be prepared with... 

Damrauer, N. H. McCusker, J. K. Ultrafast dynamics in the metal-to-ligand charge transfer excited-state evolution of Ru(4,4 -diphenyl-2,2 - bipyridine)(3) (2+). J. Phys. Chem. A 1999, 103, 8440-8446. 

Some photosensitizers, such as metal organic complexes (see also Section 6.8), can behave as either electron donors or acceptors because of their favourable redox potentials for oxidation or reduction of their excited states.670 A well-known example is tris(2,2 -bipyridine)ruthenium(II) ion ([Ru(bpy)3]2 + Scheme 6.204).10461235 When a solution of this compound is irradiated with visible light, a triplet charge-transfer excited state is formed, in which a metal-centred electron is promoted to the jt -orbital of the bipyridyl ligand [d,7t state where the metal is the electron-deficient centre (acceptor) and the ligand is the electron rich centre (donor)]. 

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