Thermodynamics of Supramolecular Naphthalenediimide Nanotube Formation: The Influence of Solvents, Side Chains, and Guest Templates

Amino-acid functionalized naphthalenediimides self-assemble into hydrogen-bonded supramolecular helical nanotubes via a noncooperative, isodesmic process; the self-assembly of ordered helical systems is usually realized through a cooperative process. This unexpected behavior was rationalized as a manifestation of entropy–enthalpy compensation. Fundamental insights into the thermodynamics governing this self-assembly were obtained through the fitting of the isodesmic model to 1H NMR spectrometry and circular dichroism spectroscopy measurements. Furthermore, we have extended the application of this mathematical model, for the first time, to quantitatively estimate the effect of guests, solvents, and side chains on the stability of the supramolecular nanotube; most significantly, we demonstrate that C60 acts as a template to stabilize the nanotube assembly and thereby substantially increase the degree of polymerization.

氨基酸功能化萘二酰亚胺（amino-acid functionalized naphthalenediimides）通过非协同、等缔合过程（isodesmic process）自组装形成氢键合超分子螺旋纳米管；而有序螺旋体系的自组装通常依赖协同过程完成。这一反常行为被合理阐释为熵焓补偿（entropy–enthalpy compensation）效应的具体体现。通过将等缔合模型拟合至核磁共振氢谱（1H NMR spectrometry）与圆二色谱（circular dichroism spectroscopy）的测试数据，我们对调控该自组装过程的热力学机制获得了基础性认知。此外，我们首次将该数学模型的应用范畴拓展，用以定量评估客体分子、溶剂与侧链对超分子纳米管稳定性的影响；尤为关键的是，我们证实C60可作为模板稳定纳米管组装体，进而显著提升聚合度。