Interaction of triplet C60 with p-tert-butyl-calixarenes and their complexes with pyridine derivatives

Abstract

The interaction of triplet excited C₆₀ with p-tert-butyl-calix[n]arenes (BCXn, n = 4, 6 or 8) and with their 2,4,6-trimethylpyridine (TMP) and pyridine complexes has been studied with laser flash photolysis experiments. It has been found that in polar solvents ³C₆₀ is quenched by BCX6 via electron transfer, producing C₆₀⁻˙ radical anion with a yield of 0.45 ± 0.07 in benzonitrile. In contrast, no reaction occurs in nonpolar media or with BCX4 and BCX8. Upon the addition of TMP, the rate of quenching is enhanced considerably due to the formation of TMP-BCXn complexes. The significant deuterium isotope effect indicates that the electron movement from the calixarene to the triplet excited C₆₀ is coupled to the proton displacement from the calixarene to the base. In the presence of pyridine, which has weaker hydrogen-bonding power, the enrichment of the solvate shell in the proton acceptor molecules may play an important role in promoting triplet C₆₀ quenching.