Ultrafast electron transfer, recombination and spin dynamics

Gilch, Peter; Pöllinger-Dammer, Florian; Steiner, Ulrich; Michel‐Beyerle, M. E.

doi:10.1016/s0009-2614(97)00755-0

Cited by 12 publications

(12 citation statements)

References 25 publications

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“…To emphasize the point, the Marcus reorganization energy (λ inner ) of the 2 → 2 + oxidation (Table S2) was calculated (see Supporting Information) and found to be 0.143 eV. This small value is on the order of the experimentally measured Fc → Fc + λ inner of ∼0.1 eV , and much smaller than the already small λ inner reported by Karlin and co-workers for [Cu(II) 2 (UN-O)(O 2 •– )] 2+ → [Cu(II) 2 (UN-O)(O 2 •– )] + that was experimentally determined to be ∼0.4 eV . The minimal change in structure upon oxidation suggests that the electron transfer kinetics of the 2 / 2+ conversion will be fast.…”

Section: Results and Analysismentioning

confidence: 78%

“…To emphasize the point, the Marcus reorganization energy (λ inner ) 81 of the 2 → 2 + oxidation (Table S2) was calculated (see Supporting Information) 82 and found to be 0.143 eV. This small value is on the order of the experimentally measured Fc → Fc + λ inner of ∼0.1 eV 83,84 and much smaller than the already small λ inner reported by Karlin and co-workers for [Cu (II)…”

Section: Results and Analysismentioning

confidence: 79%

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Exceptionally High O–H Bond Dissociation Free Energy of a Dicopper(II) μ-Hydroxo Complex and Insights into the Geometric and Electronic Structure Origins Thereof

et al. 2020

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The strength of the relevant bonds in bond-making and bond-breaking processes can directly affect the overall efficiency of the process. Copper–oxygen sites are known to catalyze reactions with some of the most recalcitrant C–H bonds found in nature as quantified by the bond dissociation free energy (BDFE), yet only a handful of copper-bound O–H bond strengths have been defined. Equally important in the design of synthetic catalysts is an understanding of the geometric and electronic structure origins of these thermodynamic parameters. In this report, the BDFE(OH) of two dicopper–hydroxo complexes, {[LCu]2-(μ-OH)}3+ and {[LCu]2-(μ-OH)}4+ (L = tris(2-pyridylmethyl)amine), were measured. Two key observations were made: (i) the BDFE(OH)s of these complexes were exceptionally high at 103.4 and 91.7 kcal/mol, respectively, which are the highest condensed phase MO-H BDFEs to date and (ii) that the higher oxidation state had a lower BDFE(OH), which is counter to expectations based on known mononuclear BDFE(OH)s which increase with the oxidation state. To understand the origin of these thermodynamic values, the BDFE(OH)s were measured and analyzed for the mononuclear complexes [LCu(OH2)]1+ and [LCu(OH2)]2+ in the same ligand environment. This treatment revealed “dinuclear effects” that include contributions from rehybridization of the oxygen, mixed valency of the metals, magnetic exchange between the metals, and differences in solvation, which are general with respect to [M]2–OH complexes to varying degrees. These analyses are important because they provide a starting point for rationally tuning the thermodynamics of catalytic intermediates broadly and for understanding how copper active sites achieve activation of strong C–H bonds.

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Section: Results and Analysismentioning

confidence: 78%

Section: Results and Analysismentioning

confidence: 79%

Exceptionally High O–H Bond Dissociation Free Energy of a Dicopper(II) μ-Hydroxo Complex and Insights into the Geometric and Electronic Structure Origins Thereof

et al. 2020

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“…For the ferrocenium + /(methylene blue) • system, a value of 1.5 ps was derived for the time constant of backward electron transfer . In fact, direct time-resolved observations in similar systems ( N , N -dimethylaminoferrocenium + /(methylene blue) • 1 ps, ethylferrocenium + /oxonine • , 0.6 ps 20 ) yielded reaction time constants close to that value.…”

Section: Referencesmentioning

confidence: 86%

Temperature-Dependent Spin Relaxation: A Major Factor in Electron Backward Transfer Following the Quenching of *Ru(bpy)₃²⁺ by Methyl Viologen

et al. 2001

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The magnetic-field dependence of the cage escape efficiency ( ce ) of [Ru(bpy) 3 ] 3+ and methyl viologen radicals (MV +• ) from the primary redox pair formed upon quenching of photoexcited [Ru(bpy) 3 ] 2+ by MV 2+ was measured by laser flash spectroscopy in aqueous solution as a function of the magnetic field (0-2.85 T) in the temperature range from 5 to 69°C. Furthermore, the 1 H NMR T 1 times of the paramagnetic [Ru(bpy) 3 ] 3+ were measured between -40 and 42°C. The kinetic data were analyzed in terms of a kinetic model that takes into account spin conservation in the forward reaction between the 3 MLCT state of [Ru(bpy) 3 ] 2+ and the electron acceptor MV 2+ yielding a triplet spin-correlated radical pair (RP) and the in-cage backward electron transfer requiring singlet character of the RP. The triplet-to-singlet spin conversion of the geminate RP is explicitly treated by the stochastic Liouville equation formalism. By theoretical simulation of the observed magnetic field dependence of ce , the temperature dependent absolute values of the rate constants k ce (cage escape), k bet (backward electron transfer in singlet RPs), and k TS (magnetic-field independent triplet-to-singlet interconversion) could be assessed. The temperature dependence of k ce exhibits a very good proportionality to the solvent viscosity. The values obtained for k TS are in good agreement with the results on the electron spin relaxation time of [Ru(bpy) 3 ] 3+ derived by the Solomon relation from the 1 H NMR T 1 times. The effective rate of backward electron transfer in the geminate RP turns out to be close to spin-controlled, i.e., it is determined by the rate constant k TS of the triplet-singlet spin conversion process. The true rate constant k bet , varying from 5.5 × 10 10 s -1 to 1.2 × 10 11 s -1 , is about seven times larger than the effective value for the total backward electron transfer comprising spin conversion and spin-allowed backward electron transfer.

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“…A detailed description will be given in a forthcoming publication . The time-resolved absorption measurements were performed in the group of M. E. Michel-Beyerle at the TU München (for details of the setup, see ref ). The sample was prepared by dissolving 100 mg of I 2 and 100 mg of KI in 50 mL ethanol.…”

Section: Methodsmentioning

confidence: 99%

Photolysis of Triiodide Studied by Femtosecond Pump−Probe Spectroscopy with Emission Detection

Gilch

Hartl

2002

J. Phys. Chem. A

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The photodissociation of triiodide into diiodide and iodine in ethanol solution was studied by a novel femtosecond pump−probe technique. The dispersed emission of the triiodide sample was recorded as a function of the delay between a 407 nm pump pulse and a 815 nm probe pulse. The most prominent feature of the resulting time dependent spectra is a strong anti-Stokes (with respect to the probe wavelength) contribution. This contribution rises with a delay of ∼500 fs and decays on the 2 ps time scale. The decay of the anti-Stokes spectrum is discussed in terms of the cooling dynamics of nascent diiodide for which the technique presented here gives a more direct access than transient absorption spectroscopy.

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Ultrafast electron transfer, recombination and spin dynamics

Cited by 12 publications

References 25 publications

Exceptionally High O–H Bond Dissociation Free Energy of a Dicopper(II) μ-Hydroxo Complex and Insights into the Geometric and Electronic Structure Origins Thereof

Exceptionally High O–H Bond Dissociation Free Energy of a Dicopper(II) μ-Hydroxo Complex and Insights into the Geometric and Electronic Structure Origins Thereof

Temperature-Dependent Spin Relaxation: A Major Factor in Electron Backward Transfer Following the Quenching of *Ru(bpy)₃²⁺ by Methyl Viologen

Photolysis of Triiodide Studied by Femtosecond Pump−Probe Spectroscopy with Emission Detection

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Ultrafast electron transfer, recombination and spin dynamics

Cited by 12 publications

References 25 publications

Exceptionally High O–H Bond Dissociation Free Energy of a Dicopper(II) μ-Hydroxo Complex and Insights into the Geometric and Electronic Structure Origins Thereof

Exceptionally High O–H Bond Dissociation Free Energy of a Dicopper(II) μ-Hydroxo Complex and Insights into the Geometric and Electronic Structure Origins Thereof

Temperature-Dependent Spin Relaxation: A Major Factor in Electron Backward Transfer Following the Quenching of *Ru(bpy)32+ by Methyl Viologen

Photolysis of Triiodide Studied by Femtosecond Pump−Probe Spectroscopy with Emission Detection

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Temperature-Dependent Spin Relaxation: A Major Factor in Electron Backward Transfer Following the Quenching of *Ru(bpy)₃²⁺ by Methyl Viologen