DiiodoBodipy-Perylenebisimide
Dyad/Triad: Preparation
and Study of the Intramolecular and Intermolecular Electron/Energy
Transfer
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Abstract
2,6-diiodoBodipy-perylenebisimide
(PBI) dyad and triad were prepared,
with the iodoBodipy moiety as the singlet/triplet energy donor and
the PBI moiety as the singlet/triplet energy acceptor. IodoBodipy
undergoes intersystem crossing (ISC), but PBI is devoid of ISC, and
a competition of intramolecular resonance energy transfer (RET) with
ISC of the diiodoBodipy moiety is established. The photophysical properties
of the compounds were studied with steady-state and femtosecond/nanosecond
transient absorption and emission spectroscopy. RET and photoinduced
electron transfer (PET) were confirmed. The production of the triplet
state is high for the iodinated dyad and the triad (singlet oxygen
quantum yield Φ<sub>Δ</sub> = 80%). The Gibbs free energy
changes of the electron transfer (Δ<i>G</i><sub>CS</sub>) and the energy level of the charge transfer state (CTS) were analyzed.
With nanosecond transient absorption spectroscopy, we confirmed that
the triplet state is localized on the PBI moiety in the iodinated
dyad and the triad. An exceptionally long lived triplet excited state
was observed (τ<sub>T</sub> = 150 μs) for PBI. With the
uniodinated reference dyad and triad, we demonstrated that the triplet
state localized on the PBI moiety in the iodinated dyad and triad
is not produced by charge recombination. These information are useful
for the design and study of the fundamental photochemistry of multichromophore
organic triplet photosensitizers