Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA.
J Am Chem Soc. 2011 Mar 30;133(12):4228-31. doi: 10.1021/ja111143y. Epub 2011 Mar 8.
Colloidal ZnO nanocrystals capped with dodecylamine and dissolved in toluene can be charged photochemically to give stable solutions in which electrons are present in the conduction bands of the nanocrystals. These conduction-band electrons are readily monitored by EPR spectroscopy, with g* values that correlate with the nanocrystal sizes. Mixing a solution of charged small nanocrystals (e(-)(CB):ZnO-S) with a solution of uncharged large nanocrystals (ZnO-L) caused changes in the EPR spectrum indicative of quantitative electron transfer from small to large nanocrystals. EPR spectra of the reverse reaction, e(-)(CB):ZnO-L + ZnO-S, showed that electrons do not transfer from large to small nanocrystals. Stopped-flow kinetics studies monitoring the change in the UV band-edge absorption showed that reactions of 50 μM nanocrystals were complete within the 5 ms mixing time of the instrument. Similar results were obtained for the reaction of charged nanocrystals with methyl viologen (MV(2+)). These and related results indicate that the electron-transfer reactions of these colloidal nanocrystals are quantitative and very rapid, despite the presence of ~1.5 nm long dodecylamine capping ligands. These soluble ZnO nanocrystals are thus well-defined redox reagents suitable for studies of electron transfer involving semiconductor nanostructures.
胶态 ZnO 纳米晶体被十二胺包裹并溶解在甲苯中，可以通过光电化学充电，在纳米晶体的导带中产生电子，从而得到稳定的溶液。这些导带中的电子很容易通过电子顺磁共振（EPR）光谱监测到，g* 值与纳米晶体的尺寸相关。将带电荷的小纳米晶体（e(-)(CB):ZnO-S）溶液与不带电荷的大纳米晶体（ZnO-L）溶液混合，导致 EPR 光谱发生变化，表明电子从小纳米晶体到大纳米晶体的定量转移。EPR 光谱的反向反应（e(-)(CB):ZnO-L + ZnO-S）表明电子不会从大纳米晶体转移到小纳米晶体。监测 UV 带边缘吸收变化的停流动力学研究表明，对于 50 μM 纳米晶体的反应，在仪器的 5 ms 混合时间内完成。与带电荷的纳米晶体与甲紫精（MV(2+)）的反应得到了类似的结果。这些和相关的结果表明，尽管存在约 1.5nm 长的十二胺封端配体，这些胶体纳米晶体的电子转移反应是定量的和非常快速的。这些可溶性 ZnO 纳米晶体因此是定义明确的氧化还原试剂，适用于涉及半导体纳米结构的电子转移研究。
