Accelerated hole transfer across a molecular double barrier

Hanss, David; Walther, Mathieu E.; Wenger, Oliver S.

doi:10.1039/c0cc01591a

Cited by 35 publications

(36 citation statements)

References 32 publications

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“…64–66,70 In these systems, there is a very small energy penalty needed for injection of an electron from the donor into the bridge and electron transfer rates decrease very slowly with distance. 64 We have, therefore, in the corresponding case of the ammonia host in fluid lithium ammonia solutions, an “ ammonia liquid conductor ” reflecting the fact that charge (electron) injection from the ionized (dissolved) lithium atom 13,14 takes place into the host (ammonia) conduction band quasi-free states 10,60,61 and concomitant highly effective electron tunneling through this ‘metallic ammonia’.…”

Section: Analysis and Discussionmentioning

confidence: 99%

Electron Tunneling in Lithium–Ammonia Solutions Probed by Frequency-Dependent Electron Spin Relaxation Studies

et al. 2012

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Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multi-exponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10)×10−12 s over a temperature range 230–290K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a timescale of ca. 10−13 s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential of multi-frequency EPR measurements to interrogate the microscopic nature and dynamics of ultra fast electron transfer or quantum-tunneling processes in liquids. Our results also impact on the universal issue of the role of a host solvent (or host matrix, e.g. a semiconductor) in mediating long-range electron transfer processes and we discuss the implications of our results with a range of other materials and systems exhibiting the phenomenon of electron transfer.

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Section: Analysis and Discussionmentioning

confidence: 99%

Electron Tunneling in Lithium–Ammonia Solutions Probed by Frequency-Dependent Electron Spin Relaxation Studies

et al. 2012

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“…2 left half) to modular bridges (eqn (15)- (19)) is sketched in Fig. 4 for an oxidative photoinduced electron transfer reaction (OPET).…”

Section: Modular Bridgesmentioning

confidence: 99%

Photoinduced electron transfer across molecular bridges: electron- and hole-transfer superexchange pathways

Campagna²,

2014

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Photoinduced electron transfer plays key roles in many areas of chemistry. Superexchange is an effective model to rationalize photoinduced electron transfer, particularly when molecular bridges between donor and acceptor subunits are present. In this tutorial review we discuss, within a superexchange framework, the complex role played by the bridge, with an emphasis on differences between thermal and photoinduced electron transfer, oxidative and reductive photoinduced processes, charge separation and charge recombination. Modular bridges are also considered, with specific attention to the distance dependence of donor-acceptor electronic coupling and electron transfer rate constants. The possibility of transition, depending on the bridge energetics, from coherent donor-acceptor electron transfer to incoherent charge injection and hopping through the bridge is also discussed. Finally, conceptual analogies between bridge effects in photoinduced electron transfer and optical intervalence transfer are outlined. Selected experimental examples, instrumental to illustration of the principles, are discussed.

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“…Upon doping, they not only act as excellent organic conductors, but also as long-range electron transfer materials. 1,2 They can be used as the active component in optical devices, such as light-emitting diodes, 3 and they display liquid crystalline properties as well as a high degree of thermal stability. 4 Among them, oligo-p-phenylenes are of particular interest because, when compared with polymers, they are easily obtained by controlled organic reactions as a monodisperse material of great purity 5e8 and owing to its rigid rod-like molecular structure 9 they have been used in the construction of organic nanostructures.…”

Section: Introductionmentioning

confidence: 99%

Suzuki–Miyaura monocouplings of p-dibromobiphenyl and substituted p-dibromo(penta-p-phenylenes)

et al. 2011

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Accelerated hole transfer across a molecular double barrier

Abstract: We report on a dyad in which photoinduced hole transfer through a non-uniform molecular double barrier is more than one order of magnitude more rapid than hole transfer across a comparable uniform (rectangular) tunneling barrier.

Cited by 35 publications

References 32 publications

Electron Tunneling in Lithium–Ammonia Solutions Probed by Frequency-Dependent Electron Spin Relaxation Studies

Electron Tunneling in Lithium–Ammonia Solutions Probed by Frequency-Dependent Electron Spin Relaxation Studies

Photoinduced electron transfer across molecular bridges: electron- and hole-transfer superexchange pathways

Suzuki–Miyaura monocouplings of p-dibromobiphenyl and substituted p-dibromo(penta-p-phenylenes)

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