We design bis-diimide-based molecules to investigate the optimal geometries for Li⁺ binding in acyclic systems, and find that the average dihedral angles between the bis-diimide groups and the central core are critical factors that influence the process of binding Li⁺. By synthesizing and characterizing a series of bis-diimides with different central cores, we demonstrate that the nature of the central core can significantly affect the binding affinity for Li⁺. Specifically, the bis-diimide with a thiazole central core exhibits moderate binding affinity for Li⁺, while the one with a pyridine central core does not bind Li⁺. The single crystal structures of bis-diimides with pyridine or thiazole as central cores provide an explanation for the observed differences in binding affinity, which we attribute to variations in the average dihedral angles between the bis-diimide groups and the central cores. To further investigate the binding properties of bis-diimide with thiazole as the central core, we determine its binding constants for Li⁺ and Na⁺ using ¹H NMR titration, and it exhibits moderate selectivity for Li⁺ over Na⁺. Interestingly, single crystal X-ray diffraction analysis reveals that it forms a 2:2 complex with LiClO₄ in the solid state. In addition, the bis-diimide bearing more aromatic groups displays a 2:1 binding mode with Li⁺ at the early stage of titration due to π-π interactions. Overall, our study provides valuable insights into the design of acyclic systems with optimal geometries for Li⁺ binding, which can have important implications for the development of advanced materials for energy storage applications.

Semin Lee

Assistant Professor, Louisiana State University

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