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

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 Pd₂L₄ 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.