Aqueous solution state host−guest systems have been studied, comprising the large host cucurbit[10]uril with luminescent cationic tris(polypyridyl) (PP) metal complexes [Ru(PP) 3 ] 2+ and [Ir(PP) 3 ] 3+ . All complexes bind strongly with the host, with the overall complex charge and size having a minor effect on affinity but influencing the association dynamics and contribution from higher-order (1:2) host−guest species. The 1:2 species contributes more significantly to the binding equilibrium in the case of [Ru(phen) 3 ] 2+ . The effect of the host upon emission is highly variable and depends on the electronic structure of the guest. The metal-to-ligand charge transfer (MLCT) emission of [Ru(PP) 3 ] 2+ is strongly quenched, in contrast to the large enhancements seen previously for MLCT emission of iridium cyclometalated complexes, while the ligand-centered emission of [Ir(PP) 3 ] 3+ is little affected. The mechanisms of quenching and enhancement are discussed, together with the implications for the design of larger supramolecular assemblies based on these archetypal emitters.

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