Aqueous Accumulation and Co-Accumulation of Multiple Cationic Porphyrins within a Polyaromatic Capsule

In contrast to stable cation-anion assemblies in nonpolar solvents, neither cations nor anions assemble themselves due to electrostatic repulsion and/or hydration in bulk solution. Here we report the multiple accumulation of cationic porphyrins in water using a polyaromatic capsule formed from bent amphiphiles. Simple stirring of the aqueous capsule with cationic Au-(III)-tetraphenylporphyrins in water leads to the efficient formation of new host-guest composites, much more efficiently than that with nonionic Zn-(II) derivatives under the same conditions. The detailed UV-visible, NMR, DLS, AFM, TEM, and molecular modeling studies reveal that the accumulated multication composite is a ∼2 nm-sized spherical particle, consisting of stacked, three porphyrin cations in the capsule as a major product, through effective host-guest π-π and CH-π interactions. The theoretical analysis indicates the importance of large dispersion force-based stabilization between the cationic porphyrins. Notably, the cationic Au-(III)-porphyrins and nonionic polyaromatic compounds such as Cu-(II)-phthalocyanine and fullerene are co-accumulated efficiently in the cavity through a stepwise grinding-stirring protocol. Otherwise unstable multicationic accumulation as well as unusual cationic-nonionic co-accumulation are demonstrated in the adaptable cavity of the polyaromatic capsule even under hydratable aqueous conditions.