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Solvent-Mediated Activation/Deactivation of Photoinduced Electron-Transfer in a Molecular Dyad
Christopher B Larsen1, George A Farrow2, Liam D Smith2
1Department of Chemistry, University of Basel, St. Johanns-Ring 19, Basel CH-4056, Switzerland.
Abstract:
Herein is presented a molecular dyad comprised of a [Ru(bpy)3]2+ photosensitizer and an anthraquinone (AQ) acceptor coupled by an ethynyl linker ([Ru(bpy)2(bpy-cc-AQ)]2+) in which activation/deactivation of photoinduced electron-transfer from the [Ru(bpy)3]2+ photosensitizer to the AQ acceptor is achieved and characterized as a function of the dielectric constant and hydrogen-bond donating ability of the solvent used. It is demonstrated that the rate of photoinduced electron-transfer can be modulated over several orders of magnitude (105-1011 s-1) by choice of solvent. Nanosecond transient absorption spectra are dominated by MLCT signals and exhibit identical decay kinetics to the corresponding emission signals. Ultrafast transient absorption and time-resolved infrared spectroscopies provide direct evidence for the formation of the charge-separated (CS) state and rapid (on the order of a few picoseconds) establishment of an excited-state pseudoequilibrium.
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