Bisdonor–azaBODIPY–Fullerene
Supramolecules:
Syntheses, Characterization, and Light-Induced Electron-Transfer Studies
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Abstract
Achieving ultrafast light-induced
charge separation requires carefully
selected donor and acceptor entities often held together in a closer
proximity. In the present investigation, two tetrads featuring a near-IR-emitting
sensitizer, BF<sub>2</sub>-chelated dipyrromethene (azaBODIPY), covalently
linked to a fullerene through the central boron atom and two electron-donor
entities, namely, <i>N</i>,<i>N</i>-dimethylaminophenyl,
or bithiophene in close proximity to the fullerene entity were designed
and synthesized, and the results were compared to the earlier-reported
bisferrocene–azaBODIPY–fullerene tetrads in this series.
The tetrads synthesized by establishing a multistep procedure exhibited
typical spectral, redox, and photo reactivities of the individual
components with some degree of intramolecular interaction. The X-ray
structure of one of the precursor triads was also solved as part of
this investigation. Ultrafast photoinduced electron transfer was witnessed
in the case of both tetrads by femtosecond transient absorption spectroscopy
studies. The significance of electron-donor entities was clear for
the tetrad derived from <i>N</i>,<i>N</i>-dimethylaminophenyl
entities, while for the bithiophene-derived tetrad, the charge separation
involved mainly the azaBODIPY and fullerene entities. The charge recombination
process involved populating the triplet excited state of azaBODIPY
prior to returning to the ground state for both tetrads, as demonstrated
by nanosecond transient absorption studies