Kinetics of Intersystem Electron Transfer within Triplet Radical Ion Pairs on Silica Studied by Diffuse-Reflectance Laser Flash Photolysis. Bell-Shaped Energy Gap Dependence on the Surface

Levin, P. P.; Costa, Sı́lvia M. B.; Ferreira, L. F. Vieira

doi:10.1021/j100004a028

Cited by 18 publications

(46 citation statements)

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“…In our system, we have one charged and one neutral reactant, and therefore would predict that a small amount of electrostatic work is done in bringing the reactants together. Our value for the reorganisation energy is found to be lower than those typically found in polar solvents 37-42 and on wet silica, 47 where values in the range 0.8 to 0.95 eV (or 77 to 92 kJ mol Ϫ1 ) have been obtained. Thomas et al 20 calculated reorganisation energy values from the Stokes shifts for the pyrene and N,N-dimethylaniline charge-transfer state co-adsorbed on silica gel.…”

Section: Transient Absorption Data: Kinetics Of Energy and Electron T...contrasting

confidence: 60%

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Bimolecular processes on silica gel surfaces: energetic factors in determining electron-transfer rates

Worrall

Kirkpatrick

Williams

2004

Photochem Photobiol Sci

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Triplet state and radical cation formation is observed following laser excitation of anthracene, phenanthrene and naphthalene (and their derivatives) adsorbed on silica gel. Energy- and electron-transfer reactions of these compounds with co-adsorbed azulene have been studied using a time-resolved diffuse reflectance laser flash photolysis technique. Triplet energy transfer from the arene derivative to azulene and electron transfer from azulene to the arene radical cation have been investigated in order to distinguish between diffusional and energetic control in these systems. Energy and electron transfer can be studied independently due to differing absorption properties and energy dependencies of production of the triplet states and radical cations. Transient decay kinetics for both electron and energy transfer have been modelled using two different rate constant distributions: a log Gaussian and a symmetrical Levy stable distribution. The latter model has also been demonstrated to be applicable to the decay of radical cations in the absence of an electron donor, which cannot be adequately described by the Gaussian model. Energy-transfer rates between the arene derivatives and azulene have been found to be close to the diffusion-controlled limit; however, in most cases, the rate of electron transfer is considerably lower. A correlation between the bimolecular rate constant and free energy of electron transfer has been found, indicating a Marcus inverted region. Compounds with bulky substituents show a further reduction in the rate of electron transfer, suggesting that an additional steric factor is involved in this process.

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Section: Transient Absorption Data: Kinetics Of Energy and Electron T...contrasting

confidence: 60%

“…This has been demonstrated previously for back electron transfer in solution, 37-42 rigid matrices, 43 metal oxide systems [44][45][46] and on silica gel. 47…”

Section: Introductionmentioning

confidence: 99%

Bimolecular processes on silica gel surfaces: energetic factors in determining electron-transfer rates

Worrall

Kirkpatrick

Williams

2004

Photochem Photobiol Sci

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“…While in the case of σ-bond assistance β is often smaller than 1 Å -1 , it amounts to 2 or 3 Å -1 for intermolecular processes leading to a decrease of k et by a factor of 10 over 1 Å. Therefore, despite a shallow dependence of k et on the thickness of a LB film, observed for electron transfer through a monolayer, ,,, k et can be expected to decrease very rapidly in the plane of a monolayer. We will, therefore, assume that for only pyrene molecules situated directly opposite from a rhodamine moiety will we be able to quench its fluorescence by electron transfer.…”

Section: The Modelmentioning

confidence: 97%

“…The fluorescence quenching in monolayer assemblies is often described in the frame of a “hard sphere” model, which is based on the “Perrin” model and allows one to determine a critical radius for PET. − There is only limited information available on the influence of PET on the fluorescence decays of chromophores incorporated in mono- and multilayers. − When interlayer electron transfer is investigated, the fluorescence decay curves are generally analyzed as a sum of exponential terms . A possible reason the amount of time-resolved data are limited is the fact that, already in the absence of the electron donor or acceptor inducing quenching by PET, the fluorescence decays are often nonexponential or multiexponential. − …”

Section: Introductionmentioning

confidence: 99%

Determination of the Photoinduced Electron Transfer Rate Constant in Langmuir−Blodgett Films by Time-Resolved Fluorescence

1999

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The feasibility of a relevant analysis of the fluorescence decays of Langmuir−Blodgett−Kuhn films where electron and energy transfer occur simultaneously is demonstrated. Starting from a stretched exponential, describing Förster-type energy transfer, a model describing simultaneous photoinduced electron transfer and energy transfer is developed. In this model a binomial distribution of electron donors (pyrene) is assumed in the layer adjacent to the excited probe (Rhodamine G). When the fluorescence decays of two or three samples with different concentrations of electron donors are analyzed simultaneously with the decay of a sample containing no electron donor, reliable values of the global parameters (the fluorescence decay time of the unquenched probe, the rate constant for electron transfer, and the rate constant for energy transfer to a trap) could be obtained. The local parameters (the average number of electron donors in a site opposite the probe and the fraction of the monolayer containing an electron donor) are, however, highly correlated. For the concentration range investigated, the decay parameters do not depend on the emission wavelength.

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“…This is due to difficulties in determination of exact and reproducible experimental kinetic data for fast reactions as well as to the complexity of the interaction routes of the products and intermediates with the surface sites. The electron transfer (ET) bimolecular photoreactions are related to the simplest type of the interaction, since these processes are free from breaking and making chemical bonds. − Their rate is very sensitive to the nature of the medium (its polarity, polarizability, and donor−acceptor properties). The theory of such processes in solution is well developed, and use of modern spectral kinetic equipment enables us to gain very reproducible decay profiles of fluorescence intensity under various experimental conditions.…”

Section: Introductionmentioning

confidence: 99%

Description of Bimolecular Photoreaction Kinetics on the Heterogeneous Solid Surface

1997

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A kinetic model including the surface distributions of both radiative and nonradiative (bimolecular) rate constants has been proposed for explanation of bimodal distribution curves of apparent rate constants of bimolecular pyrene fluorescence quenching by N,N-dimethylaniline on a nonporous silica surface. Assuming that the distributions of radiative and nonradiative rate constants are uniform functions, the analytic solutions of the generalized integral equation for the decay profile and average lifetime of the fluorophore excited state have been derived. The average values and mean-square deviations for both distributions have been determined for the bimolecular pyrene fluorescence quenching on the silica surface. The proposed model may be used as a basis for detailed studies of regularities in bimolecular photoreactions on the heterogeneous solid surface.

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Kinetics of Intersystem Electron Transfer within Triplet Radical Ion Pairs on Silica Studied by Diffuse-Reflectance Laser Flash Photolysis. Bell-Shaped Energy Gap Dependence on the Surface

Cited by 18 publications

References 1 publication

Bimolecular processes on silica gel surfaces: energetic factors in determining electron-transfer rates

Bimolecular processes on silica gel surfaces: energetic factors in determining electron-transfer rates

Determination of the Photoinduced Electron Transfer Rate Constant in Langmuir−Blodgett Films by Time-Resolved Fluorescence

Description of Bimolecular Photoreaction Kinetics on the Heterogeneous Solid Surface

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