In order to find calix[n]arenes which can interact with fullerene in solution we have screened a number of different calix[n]arenes by spectroscopic methods. We eventually discovered such three calix[n)arenes (15·Bu(t)·H, 16·Bu(t)·H, and 23·Bu(t)·H) which could accept fullerene even in solution. They commonly possess a cone conformation and a benzene ring inclination suitable to fullerene inclusion. Furthermore, it was found that calix[n]aryl ester derivatives, which cannot interact with fullerene, become excellent fullerene-acceptors in the presence of certain specific metal cations. This was attributed to a metal-induced conformational change to preorganize cone calixi[n]aryl esters. This phenomenon is a sort of positive allosterism, which is the first example in fullerene chemistry. We believe that these findings will open a door to new fullerene-calix[n]arene conjugate chemistry.
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