Heindl Andreas H, Wende Raffael C, Wegner Hermann A
Institut für Organische Chemie, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 17, 35392 Gießen, Germany.
Beilstein J Org Chem. 2018 May 29;14:1238-1243. doi: 10.3762/bjoc.14.106. eCollection 2018.
The understanding and control of the light-induced isomerization of azobenzenes as one of the most important classes of molecular switches is crucial for the design of light-responsive materials using this entity. Herein, we present the stabilization of metastable ()-azobenzenes by London dispersion interactions, even in the presence of comparably stronger hydrogen bonds in various solvents. The → isomerization rates of several -substituted 4,4'-bis(4-aminobenzyl)azobenzenes were measured. An intramolecular stabilization was observed and explained by the interplay of intramolecular amide and carbamate hydrogen bonds as well as London dispersion interactions. Whereas in toluene, 1,4-dioxane and -butyl methyl ether the hydrogen bonds dominate, the variation in stabilization of the different substituted azobenzenes in dimethyl sulfoxide can be rationalized by London dispersion interactions. These findings were supported by conformational analysis and DFT computations and reveal low-energy London dispersion forces to be a significant factor, even in the presence of hydrogen bonds.
作为最重要的分子开关类别之一，对偶氮苯光致异构化的理解和控制对于使用该实体设计光响应材料至关重要。在此，我们展示了通过伦敦色散相互作用实现亚稳态（）-偶氮苯的稳定化，即使在各种溶剂中存在相对较强的氢键时也是如此。测量了几种 - 取代的4,4'-双（4-氨基苄基）偶氮苯的 → 异构化速率。观察到分子内稳定化现象，并通过分子内酰胺和氨基甲酸酯氢键以及伦敦色散相互作用的相互作用来解释。在甲苯、1,4-二氧六环和 - 丁基甲基醚中，氢键起主导作用，而在二甲基亚砜中不同取代偶氮苯稳定化的变化可以通过伦敦色散相互作用来合理化。这些发现得到了构象分析和DFT计算的支持，并揭示了即使在存在氢键的情况下，低能量伦敦色散力也是一个重要因素。
