A Paradigmatic Change: Linking Fullerenes to Electron Acceptors

The potential of Lu3N@C80 and its analogues as electron acceptors in the areas of photovoltaics and artificial photosynthesis is tremendous. To this date, their electron-donating properties have never been explored, despite the facile oxidations that they reveal when compared to those of C60. Herein, we report on the synthesis and physicochemical studies of a covalently linked Lu3N@C80–perylenebisimide (PDI) conjugate, in which PDI acts as the light harvester and the electron acceptor. Most important is the unambiguous evidencein terms of spectroscopy and kineticsthat corroborates a photoinduced electron transfer evolving from the ground state of Lu3N@C80 to the singlet excited state of PDI. In stark contrast, the photoreactivity of a C60–PDI conjugate is exclusively governed by a cascade of energy-transfer processes. Also, the electron-donating property of the Lu3N@C80 moiety was confirmed through constructing and testing a bilayer heterojunction solar cell device with a PDI and Lu3N@C80 derivative as electron acceptor and electron donor, respectively. In particular, a positive photovoltage of 0.46 V and a negative short circuit current density of 0.38 mA are observed with PDI/Ca as anode and ITO/Lu3N@C80 as cathode. Although the devices were not optimized, the sign of the VOC and the flow direction of JSC clearly underline the unique oxidative role of Lu3N@C80 within electron donor–acceptor conjugates toward the construction of novel optoelectronic devices.