Enhanced binding strengths of acyclic porphyrin hosts with endohedral metallofullerenes

Abstract

The complementary use of spectroscopy and electrochemistry shed light onto the supramolecular interactions of calixarene scaffold bearing bisporphyrins 1 and 2 as hosts with a series of fullerenes –C₆₀, Sc₃N@C₈₀, and Lu₃N@C₈₀ – as guest molecules. Importantly, the present work shows a noticeable variation in binding strength when C₆₀ or endohedral fullerene guests are included into the bisporphyrins hosts. These sizeable differences could be clarified by computational models of the host–guest complexes, on the one hand, and a systematic investigation of the electron transfer chemistry, on the other hand. Detailed studies document an oxidative charge transfer (i.e., electron transfer from the bisporphyrin to the fullerene) for the C₆₀ inclusion complexes, while a reductive charge transfer (i.e., electron transfer from the fullerene to porphyrin) is operative in the endohedral metallofullerene host–guest complexes.