Tuning the shape anisotropy of loosely bound colloid-like ionic clusters in solution

Abstract

We characterize the influence of the ionic ratio on the dynamic self-assembly process involving a macrocyclic tetraimidazolium molecular box and small dianionic salts into highly defined, colloid-like ionic clusters in solution, called ionoids. Based on our studies utilizing dynamic light scattering (DLS) and continuous wave electron paramagnetic resonance (CW EPR) spectroscopy, we determine a region of privileged ionic ratios, which allow the formation of monodisperse, spheroidal structures of loosely bound ions in solution with adjustable (i) hydrodynamic radii between 6 nm and 12 nm and (ii) shape anisotropy. Inspired by Hertzsprung–Russell diagrams (HRDs) used in astrophysics to describe the fate of stars, we construct ionoid evolution diagrams (IEDs). IEDs are essential for grasping and describing the highly complex temporal development of these dynamically self-assembled structures in solution from the level of the individual ionic building blocks to stable clusters with a minimum lifetime of months, and thus aid in crafting future globular ionoids and anisotropic ionic clusters.