Different
Mechanisms for Hole and Electron Transfer along Identical Molecular
Bridges:
The Importance of the Initial State Delocalization
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Abstract
We
report measurements of hole and electron transfer along identical
oligo-<i>p</i>-phenylene molecular bridges of increasing
length. Although the injection barriers for hole and electron transfer
are similar, we observed striking differences in the distance dependence
and absolute magnitude of the rates of these two processes. Electron
transfer is characterized by an almost distance-independent, fast
charge-transfer rate. Hole transfer presents a much slower rate that
decreases significantly with the length of the bridge. Time-dependent
density functional calculations show that the observed differences
can be explained by the delocalization of the respective initial excitation.
The evaluation of the initial state is therefore essential when comparing
charge-transfer rates between different donor–bridge–acceptor
systems