Nanocarbons as electron donors and acceptors in photoinduced electron-transfer reactions

Nanocarbons composed of hybridized sp² carbons such as fullerenes, carbon nanotubes (CNTs), carbon nanohorns (CNHs) and graphene have been successfully utilized as electron acceptors in electron donor-acceptor hybrids for photoinduced electron-transfer reactions to mimic well the function of the photosynthetic reaction center. However, sp² hybridized nanocarbons can also be used as electron donors when higher fullerenes such as C₇₆ and C₇₈ or endohedral metallofullerenes are employed or when nanocarbons are combined with relatively strong electron acceptors. This paper focuses on photoinduced electron-transfer reactions of nanocarbons including fullerenes, CNTs, CNHs and graphene, which act as not only as electron acceptors but also as electron donors with strong electron acceptors such as tetracyanoethylene (TCNE) and tetracyano-p-quinodimethan (TCNQ) to produce the radical cations efficiently because of small reorganization energies of electron transfer. Alternatively the oxidizing ability of electron acceptors was enhanced by binding Lewis acids to the radical anions, which enabled to oxidize nanocarbons. The important roles of nanocarbons such as fullerenes, carbon nanotubes and graphenes on the stability of rapidly emerging perovskite based solar cells with high power conversion efficiency have also been discussed in this paper.