Intramolecular Light-Driven Accumulation of Reduction Equivalents by Proton-Coupled Electron Transfer
| Autor: | Oliver S. Wenger, Margherita Orazietti, Martin Kuss-Petermann, Markus Neuburger, Peter Hamm |
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| Přispěvatelé: | University of Zurich, Hamm, Peter |
| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
10120 Department of Chemistry
1303 Biochemistry Proton 1503 Catalysis 010405 organic chemistry Chemistry 1600 General Chemistry 1505 Colloid and Surface Chemistry General Chemistry 010402 general chemistry Photochemistry 01 natural sciences Biochemistry Acceptor Catalysis 0104 chemical sciences chemistry.chemical_compound Electron transfer Colloid and Surface Chemistry Intramolecular force Excited state 540 Chemistry Kinetic isotope effect Proton-coupled electron transfer Acetonitrile |
| Popis: | The photochemistry of a molecular pentad composed of a central anthraquinone (AQ) acceptor flanked by two Ru(bpy)32+ photosensitizers and two peripheral triarylamine (TAA) donors was investigated by transient IR and UV–vis spectroscopies in the presence of 0.2 M p-toluenesulfonic acid (TsOH) in deaerated acetonitrile. In ∼15% of all excited pentad molecules, AQ is converted to its hydroquinone form (AQH2) via reversible intramolecular electron transfer from the two TAA units (τ = 65 ps), followed by intermolecular proton transfer from TsOH (τ ≈ 3 ns for the first step). Although the light-driven accumulation of reduction equivalents occurs through a sequence of electron and proton transfer steps, the resulting photoproduct decays via concerted PCET (τ = 4.7 μs) with an H/D kinetic isotope effect of 1.4 ± 0.2. Moreover, the reoxidation of AQH2 seems to take place via a double electron transfer step involving both TAA+ units rather than sequential single electron transfer events. Thus, the overall charge-recombination reaction seems to involve a concerted proton-coupled two-electron oxidation of AQH2. The comparison of experimental data obtained in neat acetonitrile with data from acidic solutions suggests that the inverted driving-force effect can play a crucial role for obtaining long-lived photoproducts resulting from multiphoton, multielectron processes. Our pentad provides the first example of light-driven accumulation of reduction equivalents stabilized by PCET in artificial molecular systems without sacrificial reagents. Our study provides fundamental insight into how light-driven multielectron redox chemistry, for example the reduction of CO2 or the oxidation of H2O, can potentially be performed without sacrificial reagents. |
| Databáze: | OpenAIRE |
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