Guest encapsulation and coronene–C60 exchange in supramolecular zinc porphyrin tweezers, grids and prisms

Abstract

Using a variant of the HETPHEN concept, heteroleptic 2D and 3D metallosupramolecular structures, such as tweezer T, grid G and tetragonal prism P, were fabricated quantitatively and characterised by ¹H NMR, ¹³C NMR, ¹H–¹H COSY, DOSY as well as ESI-MS. All structures encapsulate C₆₀, with P showing the highest binding affinity (K_assoc = 3.3 × 10⁶ M⁻¹). The association constant increases along the series T < G < P, most likely due to the enhanced structural rigidity and better coplanarity of the two zinc porphyrin units. In contrast to T and G, the tetragonal prism P shows notable encapsulation of coronene (K_assoc = 1.1 × 10⁴ M⁻¹). In T and G, on the other hand, complexation of coronene is kinetically inhibited by the bulky mesityl rings at the porphyrin periphery. As illustrated in the facile displacement of coronene by C₆₀ in coronene@P to furnish C₆₀@P, P behaves as a flexible and guest-adaptive host.