Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, China.
Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, United States.
J Am Chem Soc. 2020 Mar 4;142(9):4193-4205. doi: 10.1021/jacs.9b11124. Epub 2020 Feb 19.
The realization of chiral photochemical reactions at the molecular level has proven to be a challenging task, with invariably low efficiencies originating from very small optical circular dichroism signals. On the contrary, colloidal nanocrystals offer a very large differential response to circularly polarized light when designed with chiral geometries. We propose taking advantage of this capability, introducing a novel mechanism driving surface photochemistry in a chiral nanocrystal. Plasmonic nanocrystals exhibit anomalously large asymmetry factors in optical circular dichroism (), and the related hot-electron generation shows in turn a very strong asymmetry, serving as a mechanism for chiral growth. Through theoretical modeling, we show that chiral plasmonic nanocrystals can enable chiral surface growth based on the generation of energetic (hot) electrons. Using simple and realistic phenomenological models, we illustrate how this kind of surface photochemistry can be observed experimentally. The proposed mechanism is efficient if it operates on an already strongly chiral nanocrystal, whereas our proposed mechanism does not show chiral growth for initially nonchiral structures in a solution. The asymmetry factors for the chiral effects, driven by hot electrons, exceed the values observed in chiral molecular photophysics at least 10-fold. The proposed chiral-growth mechanism for the transformation of plasmonic colloids is fundamentally different to the traditional schemes of chiral photochemistry at the molecular level.
在分子水平上实现手性光化学反应已被证明是一项具有挑战性的任务，其效率始终很低，这主要源于非常小的光学圆二色性信号。相比之下，胶体纳米晶体在采用手性几何形状设计时，对圆偏振光具有非常大的差分响应。我们建议利用这一特性，在手性纳米晶体中引入一种新的机制来驱动表面光化学反应。等离子体纳米晶体在光学圆二色性（）中表现出异常大的不对称因子，相关的热电子产生继而表现出很强的不对称性，可作为手性生长的一种机制。通过理论建模，我们表明手性等离子体纳米晶体可以基于高能（热）电子的产生来实现手性表面生长。通过使用简单而现实的唯象模型，我们说明了如何通过实验观察到这种表面光化学反应。如果该机制在手性已经很强的纳米晶体上起作用，那么该机制的效率就会很高，而我们提出的机制在手性生长方面对初始非手性溶液中的结构没有效果。由热电子驱动的手性效应的不对称因子至少比手性分子光物理中观察到的值高出 10 倍。所提出的用于转化等离子体胶体的手性生长机制与分子水平上传统的手性光化学方案在根本上不同。
