Maximizing Coordination Capsule-Guest Polar Interactions in Apolar Solvents Reveals Significant Binding

Abstract

Guest encapsulation underpins the functional properties of self-assembled capsules yet identifying systems capable of strongly binding small organic molecules in solution remains a challenge. Most coordination capsules rely on the hydrophobic effect to ensure effective solution-phase association. In contrast, we show that using non-interacting anions in apolar solvents can maximize favorable interactions between a cationic Pd₂ L₄ host and charge-neutral guests resulting in a dramatic increase in binding strength. With quinone-type guests, association constants in excess of 10⁸ m^-1 were observed, comparable to the highest previously recorded constant for a metallosupramolecular capsule. Modulation of optoelectronic properties of the guests was also observed, with encapsulation either changing or switching-on luminescence not present in the bulk phase.

Keywords: coordination capsules; host-guest systems; non-coordinating anions; quinones; self-assembly.