A new
donor–acceptor dyad composed of a BODIPY (4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene) donor and a fullerene C60 acceptor
has been synthesized and characterized. This derivative has been prepared
using a clickable fullerene building block that bears an alkyne moiety
and a maleimide unit. The post-functionalization of the maleimide
group by a BODIPY thiol leads to a BODIPY-C60 dyad, leaving
the alkyne moiety for further functional arrangement. On the basis
of the combination of semi-empirical and density functional theory
(DFT) calculations, spectroelectrochemical experiments, and steady-state
and time-resolved spectroscopies, the photophysical properties of
this new BODIPY-C60 dyad were thoroughly studied. By using
semi-empirical calculations, the equilibrium of three conformations
of the BODIPY-C60 dyad has been deduced, and their molecular
orbital structures have been analyzed using DFT calculations. Two
short fluorescence lifetimes were attributed to two extended conformers
displaying variable donor–acceptor distances (17.5 and 20.0
Å). Additionally, the driving force for photoinduced electron
transfer from the singlet excited state of BODIPY to the C60 moiety was calculated using redox potentials determined with electrochemical
studies. Spectroelectrochemical measurements were also carried out
to investigate the absorption profiles of radicals in the BODIPY-C60 dyad in order to assign the transient species in pump–probe
experiments. Under selective photoexcitation of the BODIPY moiety,
occurrences of both energy and electron transfers were demonstrated
for the dyad by femtosecond and nanosecond transient absorption spectroscopies.
Photoinduced electron transfer occurs in the folded conformer, while
energy transfer is observed in extended conformers.
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