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

Abstract

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.