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Hydrogen-Bonding Effects on the Formation and Lifetimes of Charge-Separated States in Molecular Triads

Hankache, Jihane and Niemi, Marja and Lemmetyinen, Helge and Wenger, Oliver S.. (2012) Hydrogen-Bonding Effects on the Formation and Lifetimes of Charge-Separated States in Molecular Triads. Journal of Physical Chemistry A, 116 (31). pp. 8159-8168.

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Official URL: http://edoc.unibas.ch/48169/

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Abstract

Photoinduced electron transfer in two molecular triads comprised of a triarylamine donor, a d6 metal diimine photosensitizer, and a 9,10-anthraquinone acceptor was investigated with particular focus on the influence of hydrogen-bonding solvents on the electron transfer kinetics. Photoexcitation of the ruthenium(II) and osmium(II) sensitizers of these triads leads to charge-separated states containing an oxidized triarylamine unit and a reduced anthraquinone moiety. The kinetics for formation of these charge-separated states were explored by using femtosecond transient absorption spectroscopy. Strong hydrogen bond donors such as hexafluoroisopropanol or trifluoroethanol cause a thermodynamic and kinetic stabilization of these charge-separated states that is attributed to hydrogen bonding between alcoholic solvent and reduced anthraquinone. In the ruthenium triad this effect leads to a lengthening of the lifetime of the charge-separated state from ∼750 ns in dichloromethane to ∼3000 ns in hexafluoroisopropanol while in the osmium triad the respective lifetime increases from ∼50 to ∼2000 ns between the same two solvents. In both triads the lifetime of the charge-separated state correlates with the hydrogen bond donor strength of the solvent but not with the solvent dielectric constant. These findings are relevant in the greater context of solar energy conversion in which one is interested in storing light energy in charge-separated states that are as long-lived as possible. Furthermore they are relevant for understanding proton-coupled electron transfer (PCET) reactivity of electronically excited states at a fundamental level because changes in hydrogen-bonding strength accompanying changes in redox states may be regarded as an attenuated form of PCET.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Anorganische Chemie (Wenger)
UniBasel Contributors:Wenger, Oliver
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
ISSN:1089-5639
e-ISSN:1520-5215
Note:Publication type according to Uni Basel Research Database: Journal article -- The final publication is available at American Chemical Society, see DOI link
Language:English
Identification Number:
Last Modified:13 Jun 2018 06:53
Deposited On:05 Jan 2017 10:13

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