From Close Contact to Long‐Range Intramolecular Electron Transfer

Verhoeven, J. W.

doi:10.1002/9780470141656.ch13

Cited by 60 publications

(10 citation statements)

References 101 publications

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“…Two main motivations can be distinguished. The first is to increase the basic understanding of ET as one of the simplest chemical reactions. − Compared to intermolecular processes, intramolecular ET offers the advantage that the distance and mutual orientation of the electron donating (D) and accepting (A) units can be unique and controlled, at least in some cases. Therefore, the reaction takes place without diffusion of the reactants and the experimentally observed dynamics can be directly compared with theoretical ET models.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Elementary Photochemical Processes of Organic Molecules in Liquid Solution

et al. 2016

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Ultrafast photochemical reactions in liquids occur on similar or shorter time scales compared to the equilibration of the optically populated excited state. This equilibration involves the relaxation of intramolecular and/or solvent modes. As a consequence, the reaction dynamics are no longer exponential, cannot be quantified by rate constants, and may depend on the excitation wavelength contrary to slower photochemical processes occurring from equilibrated excited states. Such ultrafast photoinduced reactions do no longer obey the Kasha-Vavilov rule. Nonequilibrium effects are also observed in diffusion-controlled intermolecular processes directly after photoexcitation, and their proper description gives access to the intrinsic reaction dynamics that are normally hidden by diffusion. Here we discuss these topics in relation to ultrafast organic photochemical reactions in homogeneous liquids. Discussed reactions include intra- and intermolecular electron- and proton-transfer processes, as well as photochromic reactions occurring with and without bond breaking or bond formation, namely ring-opening reactions and cis-trans isomerizations, respectively.

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Section: Introductionmentioning

confidence: 99%

Ultrafast Elementary Photochemical Processes of Organic Molecules in Liquid Solution

et al. 2016

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“…Both covalent binding and self-assembly methods have been employed in the design of donor–acceptor hybrids capable of undergoing photoinduced electron-transfer events. − Among the self-assembly approaches, a “relatively simple” metal–ligand axial coordination approach involving porphyrins or phthalocyanines with coordinatively unsaturated metal ions such as zinc and magnesium and fullerene with a pyridine or imidazole functionality is one of the widely used methods . Using this approach, simple donor–acceptor dyads to elegant multimodular models performing complex antenna–reaction center mimicry have been successfully demonstrated. − ,− More recently, this approach has been successfully utilized to immobilize sensitizers on mesoporous TiO 2 for supramolecular dye-sensitized solar cell applications . In the present study, we have utilized this approach to assemble donor–acceptor dyads involving high potential zinc porphyrins to verify their ability to function as electron donors and to derive structure–activity relationships as applicable for dyads formed by the axial coordination method.…”

Section: Introductionmentioning

confidence: 99%

Electron Transfer Studies of High Potential Zinc Porphyrin–Fullerene Supramolecular Dyads

et al. 2014

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The ability of high oxidation potential zinc porphyrins acting as electron donors in photoinduced electron-transfer reactions is investigated. Donor−acceptor dyads were assembled via metal−ligand axial coordination of either pyridine or phenylimidazole functionalized fulleropyrrolidine with zinc porphyrin functionalized with different numbers of halogen substituents on the meso-aryl rings. Optical absorption studies on complex formation revealed relatively higher binding constants. Efficient quenching of fluorescence was observed for the newly assembled dyads, revealing their ability to undergo photoinduced events. Differential pulse voltammetry studies were performed to understand the structure−activity relationships with respect to the electron deficient nature of the porphyrins and to utilize these data to estimate free-energy change for charge-separation and charge-recombination processes. The absolute value of free-energy change for charge separation was found to be lower for halogenated porphyrins with higher oxidation potentials expecting to form high-energy radical ion pairs. Using femtosecond transient techniques, evidence for charge separation and kinetics of charge separation and recombination were obtained in toluene. The kinetic data obtained by analyzing the time profiles of the radical ions revealed occurrence of ultrafast charge separation and relatively slower charge recombination processes in the dyads. Notably, electron-transfer rates did not exactly follow the trends predicted based on Marcus theory of electron transfer. Donor− acceptor geometry and populating the triplet excited states of the sensitizers during charge recombination are considered to be possible reasons for this behavior.

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“…Supramolecular multimodular donor–acceptor systems assembled using different photo- and redox-active species have been extensively studied in the last three decades to exploit the mechanistic details of electron transfer under various conditions. − Such well-designed and assembled multimodular systems have been found to be useful in solar-fuel and solar-electricity generation and in building optoelectronic devices. − Conventionally, the synthetic analog of natural chlorophyll pigments, porphyrins, and phthalocyanines has extensively been used as light-energy-harvesting antenna and electron donor entities in these multimodular systems performing photoinduced energy- and electron-transfer reactions. − Fullerene, C 60 , due to delocalization of charges within the spherical carbon structure of the rigid aromatic π-sphere has captured special attention as novel electron-acceptor molecule. − The small reorganization energies of fullerenes in electron-transfer reactions result in fast charge separation and relatively slow charge recombination, yielding long-lived charge separated states. − …”

Section: Introductionmentioning

confidence: 99%

Preferential Through-Space Charge Separation and Charge Recombination in V-Type Configured Porphyrin–azaBODIPY–Fullerene Supramolecular Triads

et al. 2014

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Electron transfer is one of the most fundamental and prevalent processes occurring in chemistry, physics, and biology. In donor–acceptor systems with one of the partners’ a photosensitizer, upon photoexcitation, transfer of an electron between the photoexcited and ground-state molecules occurs. Factors affecting the geometry, energetics, and dynamics of this process have been one of the intensively studied scientific topics, often by building model donor–acceptor conjugates or by utilizing natural systems. A wealth of information, applicable to almost all areas of modern science and technology, has been generated from these studies. In the present study, we demonstrate preferential through-space charge separation and charge recombination in supramolecular triads composed of porphyrin (free-base, zinc, or magnesium at the central cavity) as excited-state electron donor, BF2-chealted azadipyrromethene (azaBODIPY), and fullerene (C60) as electron acceptors. Because of spatial close proximity of the terminal porphyrin and fullerene entities of the triads as a consequence of the V-type configuration, photoinduced charge separation from the singlet excited porphyrin involves fullerene instead of energetically more favorable covalently linked azaBODIPY entity. Interestingly, charge recombination also follows this path of through-space instead of an electron migration from the fullerene anion radical to the covalently linked azaBODIPY entity. The present study highlights the importance of geometric disposition of donor and acceptor entities in governing not only the forward photoinduced electron transfer but also the dark reverse electron transfer in multimodular donor–acceptor conjugates, applicable toward light-energy-harvesting and building optoelectronic devices.

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From Close Contact to Long‐Range Intramolecular Electron Transfer

Cited by 60 publications

References 101 publications

Ultrafast Elementary Photochemical Processes of Organic Molecules in Liquid Solution

Ultrafast Elementary Photochemical Processes of Organic Molecules in Liquid Solution

Electron Transfer Studies of High Potential Zinc Porphyrin–Fullerene Supramolecular Dyads

Preferential Through-Space Charge Separation and Charge Recombination in V-Type Configured Porphyrin–azaBODIPY–Fullerene Supramolecular Triads

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