Does a nitrogen matter? Synthesis and photoinduced electron transfer of perylenediimide donors covalently linked to C₅₉N and C₆₀ acceptors

The first perylenediimide (PDI) covalently linked to an azafullerene (C₅₉N) is described. PDI-C₅₉N and PDI-C₆₀ dyads where PDI acts as an electron-donor moiety have been synthesized by connection of the balls to the PDI 1-bay position. Photoexcitation of the PDI unit in both systems results in formation of the charge-separated state by photoinduced electron transfer from the singlet excited state of the PDI moiety to the C₅₉N or to the C₆₀ moiety. The charge-separated state has a lifetime of 400 ps in the case of PDI-C₅₉N and 120 ps for the PDI-C₆₀ dyad in benzonitrile at 298 K. This result has significant implications for the design of organic solar cells based on covalent donor-acceptor systems using C₅₉N as an electron acceptor, indicating that longer-lived charge-separated states can be attained using C₅₉N systems instead of C₆₀ systems.