Department of Organic Chemistry , Weizmann Institute of Science , Rehovot 76100 , Israel.
Department of Chemistry , University of Illinois at Chicago , Chicago , Illinois 60607 , United States.
J Am Chem Soc. 2019 Feb 6;141(5):1949-1960. doi: 10.1021/jacs.8b09638. Epub 2019 Jan 25.
The reversible photoisomerization of azobenzene has been utilized to construct a plethora of systems in which optical, electronic, catalytic, and other properties can be controlled by light. However, owing to azobenzene's hydrophobic nature, most of these examples have been realized only in organic solvents, and systems operating in water are relatively scarce. Here, we show that by coadsorbing the inherently hydrophobic azobenzenes with water-solubilizing ligands on the same nanoparticulate platforms, it is possible to render them essentially water-soluble. To this end, we developed a modified nanoparticle functionalization procedure allowing us to precisely fine-tune the amount of azobenzene on the functionalized nanoparticles. Molecular dynamics simulations helped us to identify two distinct supramolecular architectures (depending on the length of the background ligand) on these nanoparticles, which can explain their excellent aqueous solubilities. Azobenzenes adsorbed on these water-soluble nanoparticles exhibit highly reversible photoisomerization upon exposure to UV and visible light. Importantly, the mixed-monolayer approach allowed us to systematically investigate how the background ligand affects the switching properties of azobenzene. We found that the nature of the background ligand has a profound effect on the kinetics of azobenzene switching. For example, a hydroxy-terminated background ligand is capable of accelerating the back-isomerization reaction by more than 6000-fold. These results pave the way toward the development of novel light-responsive nanomaterials operating in aqueous media and, in the long run, in biological environments.
偶氮苯的可逆光致异构化已被用于构建大量的系统，通过光可以控制这些系统的光学、电子、催化和其他性质。然而，由于偶氮苯的疏水性，这些例子大多仅在有机溶剂中实现，而在水中运行的系统相对较少。在这里，我们表明，通过在相同的纳米颗粒平台上将疏水性的偶氮苯与水溶性配体共吸附，可以使它们本质上是水溶性的。为此，我们开发了一种改进的纳米颗粒功能化程序，使我们能够精确地微调功能化纳米颗粒上的偶氮苯含量。分子动力学模拟帮助我们确定了这两种纳米颗粒上的两种不同的超分子结构（取决于背景配体的长度），这可以解释它们优异的水溶性。吸附在这些水溶性纳米颗粒上的偶氮苯在暴露于紫外光和可见光时表现出高度可逆的光致异构化。重要的是，混合单层方法使我们能够系统地研究背景配体如何影响偶氮苯的开关性能。我们发现，背景配体的性质对偶氮苯开关的动力学有深远的影响。例如，羟基封端的背景配体能够将后异构化反应的速率加快 6000 多倍。这些结果为在水介质中运行的新型光响应纳米材料的开发铺平了道路，并从长远来看，为生物环境中的应用铺平了道路。
