Charge migration (CM) is a coherent attosecond process
that involves
the movement of localized holes across a molecule. To determine the
relationship between a molecule’s structure and the CM dynamics
it exhibits, we perform systematic studies of para-functionalized
bromobenzene molecules (X–C6H4–R)
using real-time time-dependent density functional theory. We initiate
valence-electron dynamics by emulating rapid strong-field ionization
leading to a localized hole on the bromine atom. The resulting CM,
which takes on the order of 1 fs, occurs via an X localized →
C6H4 delocalized → R localized mechanism.
Interestingly, the hole contrast on the acceptor functional group
increases with increasing electron-donating strength. This trend is
well-described by the Hammett σ value of the group, which is
a commonly used metric for quantifying the effect of functionalization
on the chemical reactivity of benzene derivatives. These results suggest
that simple attochemistry principles and a density-based picture can
be used to predict and understand CM.
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