Bonn Annabell G, Neuburger Markus, Wenger Oliver S
Department of Chemistry, University of Basel , St. Johanns-Ring 19, CH-4056 Basel, Switzerland.
Inorg Chem. 2014 Oct 20;53(20):11075-85. doi: 10.1021/ic501620g. Epub 2014 Oct 1.
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.
合成并研究了两种带有低聚三芳基胺多电子供体的分子三联体,目的是获得电荷分离态,其中低聚三芳基胺被氧化两倍。这种光诱导的多个氧化还原当量的积累对于人工光合作用具有重要意义。第一个三联体由低聚三芳基胺和两个铼(I)三羰基二亚胺光敏剂组成,每个光敏剂都有可能接受一个电子。在第二个三联体中,低聚三芳基胺通过一个铼(I)三羰基二亚胺单元与蒽醌相连,蒽醌原则上是一个双电子受体。通过纳秒瞬态吸收光谱法(使用普通的泵浦-探测技术),未发现生成两倍氧化的低聚三芳基胺或两倍还原的蒽醌的证据。讨论了将新三联体的光化学限制为单电子和单空穴简单电荷分离的关键因素,并且从该研究中获得的见解对于纯分子(无纳米颗粒)系统中电荷积累领域的进一步研究是有用的。这里考虑的铼基系统中的一个重要问题是光激发所需的短波长。在第二个三联体中,光生蒽醌单阴离子被有机酸质子化,并且产生的半醌物种使电荷分离态的寿命增加约一个数量级。这表明醌的质子耦合电子转移化学可能有利于光诱导电荷积累。