Expanded Rosarin: A Versatile Fullerene (C₆₀) Receptor

Abstract

An expanded rosarian (P₃P₆) with a bowl-like conformation has been prepared and characterized in a one-pot procedure that involves condensing a bispyrrole pyridine precursor (P₁P₂) with benzaldehyde, followed by oxidation. Single crystal X-ray diffraction analysis reveals a bowl-like conformation in the solid state with an upper rim diameter defined by the meso-phenyl substituents of ca. 13.5 Å and a depth of roughly 6.3 Å. P₃P₆ forms both 1:1 and 2:1 complexes with C₆₀ in the solid state. DFT reveals similar energies for the two binding modes. A 1:1 binding stoichiometry dominates in 1,2-dichlorobenzene-d₄ at the millimolar concentrations dictated by solubility consideration. The solution phase interactions between rosarian and C₆₀ were studied using ¹H NMR, UV-vis, and femtosecond transient absorption spectroscopies in 1,2-dichlorobenzene-d₄ or toluene. To our knowledge, this is the first report of an unfunctionalized porphyrinoid that forms a well-defined complex with C₆₀ in solution as well as in solid state.