Intramolecular charge shift following bimolecular reductive quenching of a rhodium(III) polypyridine-diquat dyad

Indelli, María Teresa; Polo, Eleonora; Bignozzi, Carlo Alberto; Scandola, Franco

doi:10.1021/j100163a002

Cited by 6 publications

(3 citation statements)

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“…The distribution of molecules between the "remote" and "adjacent" excited states is given by a Boltzmann relationship and will depend upon the energy difference between them. If equilibrium is rapidly established on the electron transfer time scale, the observed rate constant for forward charge transfer (k°bs) is approximated as the average of the rate constant for charge transfer from the two states, weighted by their populations a and a -1, eq 13. k°bs = kf(a) + kT;m(a -1) (13) Considering the above arguments, our observation of a discrete "break" point in the forward charge transfer kinetics, between complexes 1,2,3-x-MV and 4, 5-x-MV, suggests that the relative populations of the "remote" and "adjacent" MLCT states change from predominantly "adjacent" in l-x-M through 3-x-MV to predominantly "remote" in 4-x-MV and 5-x-MV. One would expect the rate constant for charge transfer from the remote ligand, by either a through-bond or through-space mechanism, to be slow relative to that from the adjacent ligand, since both mechanisms necessarily involve a larger number of intervening bonds or greater separation distance.…”

Section: Discussionmentioning

confidence: 99%

Inter- and Intramolecular Oxidative Quenching of Mixed Ligand Tris(bipyridyl)ruthenium(II) Complexes by Methyl Viologen

Kelly¹,

Rodgers²

1995

J. Phys. Chem.

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The rate constants for photoinduced electron transfer, as well as thermal charge recombination, were measured in a series of [(4,4'-R2-2,2'-bipyridine)2Rut1(4'-(CH3)-2,2'-bipyridine-4-(CO~R'))] (R' = (CH2),MV2+) systems, in which a tris(bipyridyl)ruthenium(II) chromophore was covalently linked to a 4,4'-bipyridinium (MV*+) electron acceptor. The nature of R(R = H, CH3, COO-, COOH, CONHCH(CHd2) and the number (x = 2, 3) of intervening methylene units were varied to tune the chromophore's electronic properties, including the x* orbital energies of the 4,4'-R*-2,2'-bipyridine ligands and donor-acceptor separation distance, respectively. For a given donor-acceptor distance, x, and similar driving force, the rate constants for forward electron transfer were nearly 60 (x = 3) to 400 (x = 2) times smaller in complexes in which the two 4,4'-Rl-2,2'-bipyridine ligands were R-substituted with electron-withdrawing functional groups (R = CONHCH-(CH3)2). Charge recombination from the reduced viologen acceptor to the oxidized metal center occurs in the Marcus inverted region, with the rate constants (kb) decreasing with increasing magnitude of driving force. The kinetics of the bimolecular oxidative quenching of the electronically excited state of these mixed ligand tris(bipyridyl)ruthenium(II) complexes (R' = CH(CH&) by methyl viologen was also characterized in homogeneous aqueous solution, and the escape efficiencies were measured for separation of the redox products from the solvent cage.

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Section: Discussionmentioning

confidence: 99%

Inter- and Intramolecular Oxidative Quenching of Mixed Ligand Tris(bipyridyl)ruthenium(II) Complexes by Methyl Viologen

Kelly¹,

Rodgers²

1995

J. Phys. Chem.

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“…The simple chromophore-quencher system 24 also contains a quaternarized electron acceptor attached to a Rh(III) polypyridine unit. This dyad was designed [112] to study intramolecular charge shift processes, using a photochemical inter/intramolecular reaction scheme of the type shown in Eqs. 15-19.…”

Section: Triads and Other Complex Systemsmentioning

confidence: 99%

“…The rate constants of all the processes in the above scheme have been experimentally determined, except for that of Eq. 17, inferred from experiments on appropriate model rhodium systems (without DQ pendant unit) [112]. In particular, the intramolecular charge shift process (Eq.…”

Section: Triads and Other Complex Systemsmentioning

confidence: 99%

Photochemistry and Photophysics of Coordination Compounds: Rhodium

Indelli

Chiorboli

Scandola

Topics in Current Chemistry

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Rhodium(III) polypyridine complexes and their cyclometalated analogues display photophysical properties of considerable interest, both from a fundamental viewpoint and in terms of the possible applications. In mononuclear polypyridine complexes, the photophysics and photochemistry are determined by the interplay between LC and MC excited states, with relative energies depending critically on the metal coordination environment. In cyclometalated complexes, the covalent character of the C – Rh bonds makes the lowest excited state classification less clear cut, with strong mixing of LC, MLCT, and LLCT character being usually observed. In redox reactions, Rh(III) polypyridine units can behave as good electron acceptors and strong photo-oxidants. These properties are exploited in polynuclear complexes and supramolecular systems containing these units. In particular, Ru(II)-Rh(III) dyads have been actively investigated for the study of photoinduced electron transfer, with specific interest in driving force, distance, and bridging ligand effects. Among systems of higher nuclearity undergoing photoinduced electron transfer, of particular interest are polynuclear complexes where rhodium dihalo polypyridine units, thanks to their Rh(III)/Rh(I) redox behavior, can act as twoelectron storage components. A large amount of work has been devoted to the use of Rh(III) polypyridine complexes as intercalators for DNA. In this role, they have proven to be very versatile, being used for direct strand photocleavage marking the site of intercalation, to induce long-distance photochemical damage or dimer repair, or to act as electron acceptors in long-range electron transfer processes

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