Chen Jing, Wenger Oliver S
Department of Chemistry , University of Basel , St. Johanns-Ring 19 , CH-4056 Basel , Switzerland . Email:
Xiamen Institute of Rare Earth Materials , Chinese Academy of Sciences , Xiamen 361021 , People's Republic of China.
Chem Sci. 2015 Jun 1;6(6):3582-3592. doi: 10.1039/c5sc00964b. Epub 2015 May 1.
We demonstrate that the rates for long-range electron transfer can be controlled actively by tight anion binding to a rigid rod-like molecular bridge. Electron transfer from a triarylamine donor to a photoexcited Ru(bpy) acceptor (bpy = 2,2'-bipyridine) across a 2,5-diboryl-1,4-phenylene bridge occurs within less than 10 ns in CHCl at 22 °C. Fluoride anions bind with high affinity to the organoboron bridge due to strong Lewis base/Lewis acid interactions, and this alters the electronic structure of the bridge drastically. Consequently, a large tunneling barrier is imposed on photoinduced electron transfer from the triarylamine to the Ru(bpy) complex and hence this process occurs more than two orders of magnitude more slowly, despite the fact that its driving force is essentially unaffected by fluoride addition. Electron transfer rates in proteins could potentially be regulated a similar fundamental principle, because interactions between charged amino acid side chains and counter-ions can modulate electronic couplings between distant redox partners. In artificial donor-bridge-acceptor compounds, external stimuli have been employed frequently to control electron transfer rates, but the approach of exploiting strong Lewis acid/Lewis base interactions to regulate the tunneling barrier height imposed by a rigid rod-like molecular bridge is conceptually novel and broadly applicable, because it is largely independent of the donor and the acceptor, and because the effect is not based on a change of the driving-force for electron transfer. The principle demonstrated here can potentially be used to switch between conducting and insulating states of molecular wires between electrodes.
我们证明，通过紧密的阴离子与刚性棒状分子桥结合，可以主动控制长程电子转移速率。在22℃的CHCl中，电子从三芳基胺供体通过2,5-二硼基-1,4-亚苯基桥转移到光激发的Ru(bpy)受体（bpy = 2,2'-联吡啶），整个过程在不到10纳秒内完成。由于强烈的路易斯碱/路易斯酸相互作用，氟阴离子与有机硼桥具有高亲和力，这极大地改变了桥的电子结构。因此，从三芳基胺到Ru(bpy)配合物的光诱导电子转移受到很大的隧穿势垒限制，尽管其驱动力基本不受氟化物添加的影响，但该过程发生的速度要慢两个数量级以上。蛋白质中的电子转移速率可能受类似的基本原理调控，因为带电氨基酸侧链与抗衡离子之间的相互作用可以调节远距离氧化还原伙伴之间的电子耦合。在人工供体-桥-受体化合物中，人们经常采用外部刺激来控制电子转移速率，但利用强路易斯酸/路易斯碱相互作用来调节由刚性棒状分子桥施加的隧穿势垒高度的方法在概念上是新颖的且具有广泛适用性，因为它在很大程度上独立于供体和受体，并且这种效应不是基于电子转移驱动力的变化。这里展示的原理有可能用于在电极之间的分子导线的导电和绝缘状态之间进行切换。
