The photoisomerization properties of a series of cyclic azobenzene (cAb) analogs, including non‐substituted, Br‐, CN‐, carboxyl‐, and amino cAb, were compared. While the trans‐form of these analogs show different degrees of thermal stability, no spectral changes in the absorption wavelengths were observed for amino cAb upon exposure to purple light. The ¹⁵N NMR chemical shifts of cAb in both cis‐ and trans‐forms were found to show a large difference from those of aromatic azobenzene; however, the trend of difference in chemical shift is in agreement with that obtained from quantum chemical calculations. More importantly, the structure of the photoisomerization product from cis‐cAb was confirmed to be, indeed, the trans‐cAb by X‐ray diffraction experiments. The ¹⁵NMR data of the cAb isomers and confirmation of trans‐cAb through crystal structure will be of importance for future studies in the design and applications of cAb as a photoswitch.

中文翻译：

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X-射线晶体学和环状偶氮苯类似物的光谱表征确定反式-环偶氮苯的结构

比较了一系列环状偶氮苯（cAb）类似物的光异构化特性，包括未取代的Br-，CN-，羧基和氨基cAb。虽然反这些类似物的构型中显示出不同程度的热稳定性，观察在暴露于紫光氨基驾驶室的吸收波长没有光谱的变化。发现顺式和反式两种形式的cAb的¹⁵ N NMR化学位移与芳族偶氮苯显示出很大的差异。然而，化学位移差异的趋势与从量子化学计算获得的趋势一致。更重要的是，顺式的光异构化产物的结构X射线衍射实验证实‐cAb确实是反式cAb。cAb异构体的¹⁵ NMR数据以及通过晶体结构确认反式-cAb对于将来将cAb作为光开关的设计和应用的研究具有重要意义。