Mechanistic insights into two-photon-driven photocatalysis in organic synthesis

A mechanism based on the sequential absorption of two photons by the components of a redox couple has been recently proposed for catalysis of the energetically demanding reduction of aryl halides. Here, we analyze the suggested photochemical mechanism of this reaction, which employs perylenediimide...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2018, Vol.20 (12), p.8071-8076
Main Authors: Marchini, Marianna, Gualandi, Andrea, Mengozzi, Luca, Franchi, Paola, Lucarini, Marco, Cozzi, Pier Giorgio, Balzani, Vincenzo, Ceroni, Paola
Format: Article
Language:English
Subjects:
Aromatic compounds
Catalysis
Electron paramagnetic resonance
Halides
Photocatalysis
Photochemical reactions
Photons
Photosynthesis
Reduction
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Summary:A mechanism based on the sequential absorption of two photons by the components of a redox couple has been recently proposed for catalysis of the energetically demanding reduction of aryl halides. Here, we analyze the suggested photochemical mechanism of this reaction, which employs perylenediimide (PDI) as a photocatalyst, on the basis of spectroscopic, electrochemical and electron paramagnetic resonance data. Our results indicate that the photoexcited PDI radical anion (*PDI˙ ) cannot play the role of a photosensitizer in the aforementioned process. Instead, the reduction of 4'-bromoacetophenone likely involves *PDI˙ decomposition products. The extremely short lifetime of the photoexcited transient species, as *PDI˙ , is a major general limitation for photocatalytic schemes based on sequential two-photon excitation. In order to better understand the potential of such schemes, we discuss them in the context of the Z-scheme in natural photosynthesis.
ISSN:1463-9076
1463-9084
DOI:10.1039/c7cp08011e