Drastic change in the rate of photochemical rearrangement of 1,6-(N-phenyl)aza-[60]fulleroids by switching the excited states through simple methyl substitution on the phenyl group

The reaction rate for the photochemical rearrangement of 1,6-N-(substituted-phenyl)aza-[60]fulleroid 1 to 1,2-N-(substituted-phenyl) aziridino-[60]fullerene 2 differed ca. 3000-fold depending on the position and number of methyl substituents on the N-phenyl group. The required time for the completion of the reaction decreased in the order 2,6-dimethylphenyl (1d) < 2-methylphenyl (1b) < phenyl (1a) < 4-methylphenyl (1c). The difference was mainly due to switching of the excited states between normal (fast reactions) and charge-separated (slow reactions) triplet states, which was induced by steric interactions between the N-phenyl group and the C₆₀ moiety.