Influence of halogen-halogen interactions in the self-assembly of pillar[5]arene-based supramolecular polymers

Halogen-halogen interactions play a pivotal role in the formation and stability of supramolecular assemblies. Herein, we investigate the assembly dynamics and dissociation pathways of linear supramolecular polymers based on pillar[5]arene-mediated by guest halogen-halogen interactions (C-X × X-C) in both the solution and solid states. The structure of the solid-state supramolecular assembly was determined by single-crystal X-ray diffraction analysis. The binding affinities of four different 1,4-dihalobutane guests with pillar[5]arene were investigated by ¹H NMR spectroscopic titration and isothermal titration calorimetry (ITC). The formation of the halogen-bonded linear supramolecular polymer in solution was demonstrated using diffusion-ordered spectroscopy (DOSY) and ITC. Our findings highlight the dependence of the dissociation process on halogen nature within the encapsulated guest, revealing that the process is entropically driven (TΔS = 27.12 kJ mol^-1) and enthalpically disfavored (ΔH = 9.99 kJ mol^-1). Moreover, the disassembly of supramolecular polymers promoted by N-containing compounds was investigated using ¹H NMR spectroscopy and ITC, revealing that the process is driven both enthalpically (ΔH = -2.64 kJ mol^-1) and entropically (TΔS = 15.70 kJ mol^-1). Notably, the data suggest the formation of N⋯I bonding interactions at both ends of the inclusion guest, elucidating the intricate interplay of halogen interactions and host-guest chemistry in supramolecular polymer systems.