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.