A Paradigmatic Change: Linking Fullerenes to Electron Acceptors

Abstract

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 <i>V</i>_OC and the flow direction of <i>J</i>_SC clearly underline the unique oxidative role of Lu₃N@C₈₀ within electron donor–acceptor conjugates toward the construction of novel optoelectronic devices