All-Fullerene Electron Donor-Acceptor Conjugates.

The synthesis and characterization of a covalent all-fullerene C60 -Lu3 N@Ih -C80 electron donor-acceptor conjugate has been realized by sequential 1,3-dipolar cycloaddition reactions of azomethine ylides on Lu3 N@Ih -C80 and C60 . To the best of our knowledge, this is the first time that two fullerenes behaving as both electron donor (Lu3 N@Ih -C80 ) and acceptor (C60 ) are forming an electroactive dumbbell. DFT calculations reveal up to 16 diastereomeric pairs, that is, 8 with syn and 8 with anti orientation, with the anti-RSSS isomer being the most stable. Spectroelectrochemical absorption and femtosecond transient absorption experiments support the notion that a C60 ⋅- -Lu3 N@Ih -C80 ⋅+ charge-separated state is formed. Spin conversion from the charge-separated singlet state C60 ⋅- -Lu3 N@Ih -C80 ⋅+ into the corresponding triplet state is facilitated by the heavy-atom effect stemming from the Lu3 N-cluster, which, in turn, slows down the charge recombination by one order of magnitude.