Fu Na, Gassensmith Jeremiah J, Smith Bradley D
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46545, USA.
Aust J Chem. 2010;63(5):792-796. doi: 10.1071/CH09671.
A templated macrocyclization reaction was used to permanently encapsulate a highly fluorescent hydroxy-substituted squaraine dye inside a tetralactam macrocycle. The free squaraine dye is quite rigid due to internal hydrogen bonding and its photophysical properties hardly change upon encapsulation. A combination of X-ray and NMR data show that the surrounding tetralactam macrocycle adopts an unusually rigid chair conformation and does not undergo rapid pirouetting. Because of its large size and conformational rigidity, the macrocycle creates anisotropic NMR shielding zones that extend over the N,N-dibutylamino groups at each end of the squaraine thread. This shielding anisotropy allows hindered aryl-N rotation to be observed by NMR and provides direct experimental evidence that quinoid-like resonance structures are major contributors to the bis(N,N-dialkylaminophenyl)squaraine resonance hybrid.
一种模板化大环化反应被用于将一种高荧光的羟基取代方酸染料永久封装在一个四内酰胺大环内。由于分子内氢键作用，游离的方酸染料相当刚性，其光物理性质在封装后几乎没有变化。X射线和核磁共振数据的结合表明，周围的四内酰胺大环采取了一种异常刚性的椅式构象，并且不会进行快速旋转。由于其较大的尺寸和构象刚性，大环产生了各向异性的核磁共振屏蔽区域，该区域延伸到方酸链两端的N,N-二丁基氨基上。这种屏蔽各向异性使得通过核磁共振能够观察到受阻的芳基-N旋转，并提供了直接的实验证据，证明醌型共振结构是双（N,N-二烷基氨基苯基）方酸共振杂化体的主要贡献者。
