Photoinduced Electron Transfer in Rhenium(I)–Oligotriarylamine Molecules
摘要:
Two molecular triads with an oligotriarylamine multielectron donor were synthesized and investigated with a view to obtaining charge-separated states in which the oligotriarylamine is oxidized 2-fold. Such photoinduced accumulation of multiple redox equivalents is of interest for artificial photosynthesis. The first triad was comprised of the oligotriarylamine and two rhenium(I) tricarbonyl diimine photosensitizers each of which can potentially accept one electron. In the second triad the oligotriarylamine was connected to anthraquinone, in principle an acceptor of two electrons, via a rhenium(I) tricarbonyl diimine unit. With nanosecond transient absorption spectroscopy (using an ordinary pump-probe technique) no evidence for the generation of 2-fold oxidized oligotriarylamine or 2-fold reduced anthraquinone was found. The key factors limiting the photochemistry of the new triads to simple charge separation of one electron and one hole are discussed, and the insights gained from this study are useful for further research in the area of charge accumulation in purely molecular (nanoparticle-free) systems. An important problem of the rhenium-based systems considered here is the short wavelength required for photoexcitation. In the second triad, photogenerated anthraquinone monoanion is protonated by organic acids, and the resulting semiquinone species leads to an increase in lifetime of the charge-separated state by about an order of magnitude. This shows that the proton-coupled electron transfer chemistry of quinones could be beneficial for photoinduced charge accumulation.
Microsecond charge recombination in a linear triarylamine–Ru(bpy)32+–anthraquinone triad
作者:Jihane Hankache、Oliver S. Wenger
DOI:10.1039/c1cc13831f
日期:——
Linear triads with ruthenium photosensitizers are frequently based on the Ru(terpyridine)(2)(2+) unit. We report on vectorial photoinduced electrontransfer in a linear triadbased on the Ru(bipyridine)(3)(2+) photosensitizer. Electron-hole separation over a 22 A-distance is established with a quantum yield greater than 64% and persists for 1.3 mus in acetonitrile.
Photoinduced Electron Transfer in Linear Triarylamine–Photosensitizer–Anthraquinone Triads with Ruthenium(II), Osmium(II), and Iridium(III)
作者:Jihane Hankache、Marja Niemi、Helge Lemmetyinen、Oliver S. Wenger
DOI:10.1021/ic300558s
日期:2012.6.4
A rigid rod-like organic molecular ensemble comprised of a triarylamine electron donor, a 2,2'-bipyridine (bpy) ligand, and a 9,10-anthraquinone acceptor was synthesized and reacted with suitable metal precursors to yield triads with Ru(bpy)(3)(2+), Os(bpy)(3)(2+), and [Ir(2-(p-tolyl)pyridine)(2)(bpy)](+) photosensitizers. Photoexcitation of these triads leads to long-lived charge-separated states (tau = 80-1300 ns) containing a triarylamine cation and an anthraquinone anion, as observed by transient absorption spectroscopy. From a combined electrochemical and optical spectroscopic study, the thermodynamics and kinetics for the individual photoinduced charge-separation and thermal charge-recombination events were determined; in some cases, measurements on suitable donor-sensitizer or sensitizer-acceptor dyads were necessary. In the case of the ruthenium and iridium triads, the fully charge-separated state is formed in nearly quantitative yield.