Tailoring Three-Dimensional Porphyrin Hosts to Control Fullerene Recognition and Charge-Separation

Porphyrin–fullerene assemblies are widely regarded as model systems in artificial photosynthesis. However, attaining precise structural control over both fullerene binding and charge-separation behavior within a single, rigid three-dimensional porphyrin host continues to be a significant challenge in supramolecular design. Dihydroanthracene- and triptycene-functionalized tetraarylporphyrins are shown here to act as biconcave aromatic hosts for C60, forming 1:1 and 1:2 complexes with association constants up to 104 to 105 M–1, as evidenced by 1H NMR and fluorescence titrations, and electrospray ionization mass spectrometry. Key in the host design is the porphyrin β,β-substitution that generates a well-defined and encapsulating environment for C60. Triptycenoporphyrins exhibit more geometrically confined C60 binding than their dihydroanthracene analogues, highlighting the critical role of topological control in C60 recognition. Despite identical binding strengths in nonpolar toluene and polar benzonitrile, the corresponding C60@triptycenoporphyrins display pronounced solvent-dependent excited-state behavior. Charge-separated states are generated more rapidly in benzonitrile yet attain significantly longer lifetimes in toluene, as revealed by steady-state and time-resolved spectroscopic measurements. These results demonstrate that tailoring rigid three-dimensional porphyrin frameworks enables simultaneous enhancement of C60 binding and fine control over charge-separation and -recombination dynamics, establishing this scaffold as a versatile platform for artificial photosynthetic systems that require long-lived charge-separation.