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Brandl, Fabian ; Bergwinkl, Sebastian ; Allacher, Carina ; Dick, Bernhard

Consecutive photoinduced electron transfer (conPET): The mechanism of the photocatalyst rhodamine-6G

Brandl, Fabian, Bergwinkl, Sebastian, Allacher, Carina and Dick, Bernhard (2020) Consecutive photoinduced electron transfer (conPET): The mechanism of the photocatalyst rhodamine-6G. Chemistry - A European Journal 26, pp. 7946-7954.

Date of publication of this fulltext: 22 Jan 2021 08:43
Article
DOI to cite this document: 10.5283/epub.44560


Abstract

The dye rhodamine 6G can act as a photocatalyst through photoinduced electron transfer. After electronic excitation with green light, rhodamine 6G takes an electron from an electron donor, such as N,N-diisopropylethylamine, and forms the rhodamine 6G radical. This radical has a reduction potential of around -0.90 V and can split phenyl iodide into iodine anions and phenyl radicals. Recently, it ...

The dye rhodamine 6G can act as a photocatalyst through photoinduced electron transfer. After electronic excitation with green light, rhodamine 6G takes an electron from an electron donor, such as N,N-diisopropylethylamine, and forms the rhodamine 6G radical. This radical has a reduction potential of around -0.90 V and can split phenyl iodide into iodine anions and phenyl radicals. Recently, it has been reported that photoexcitation of the radical at 420 nm splits aryl bromides into bromide anions and aryl radicals. This requires an increase in reduction potential, hence the electronically excited rhodamine 6G radical was proposed as the reducing agent. Here, we present a study of the mechanism of the formation and photoreactions of the rhodamine 6G radical by transient absorption spectroscopy in the time range from femtoseconds to minutes in combination with quantum chemical calculations. We conclude that one photon of 540 nm light produces two rhodamine 6G radicals. The lifetime of the photoexcited radicals of around 350 fs is too short to allow diffusion-controlled interaction with a substrate. A fraction of the excited radicals ionize spontaneously, presumably producing solvated electrons. This decay produces hot rhodamine 6G and hot rhodamine 6G radicals, which cool with a time constant of around 10 ps. In the absence of a substrate, the ejected electrons recombine with rhodamine 6G and recover the radical on a timescale of nanoseconds. Photocatalytic reactions occur only upon excitation of the rhodamine 6G radical, and due to its short excited-state lifetime, the electron transfer to the substrate probably takes place through the generation of solvated electrons as an additional step in the proposed photochemical mechanism.



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Details

Item typeArticle
Journal or Publication TitleChemistry - A European Journal
Publisher:Wiley
Place of Publication:WEINHEIM
Volume:26
Page Range:pp. 7946-7954
Date2020
InstitutionsChemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie
Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry III - Physical Chemistry (Molecular Spectroscopy and Photochemistry)
Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry III - Physical Chemistry (Molecular Spectroscopy and Photochemistry) > Prof. Dr. Bernhard Dick
Identification Number
ValueType
10.1002/chem.201905167DOI
KeywordsHYDRATED ELECTRONS; CATALYTIC CYCLE; LIGHT; ABSORPTION; SPECTROSCOPY; DYES; density functional calculations; electron transfer; photocatalysis; reaction mechanisms; time-resolved spectroscopy
Dewey Decimal Classification500 Science > 540 Chemistry & allied sciences
StatusPublished
RefereedYes, this version has been refereed
Created at the University of RegensburgYes
URN of the UB Regensburgurn:nbn:de:bvb:355-epub-445601
Item ID44560

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