Attochemistry Regulation of Charge Migration

TL;DR

This study uses real-time density functional theory to explore how molecular structure influences charge migration dynamics in para-functionalized bromobenzene, revealing predictable trends based on functional group properties.

Contribution

It introduces the concept of attochemistry to predict charge migration behavior using a density-based approach and correlates it with Hammett sigma values.

Findings

Charge migration occurs within 1 femtosecond via a localized-to-delocalized mechanism.

Hole contrast increases with the electron donating strength of functional groups.

Hammett sigma values effectively predict charge migration trends.

Abstract

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-C$_6$H$_4$-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 to C$_6$H$_4$ delocalized to 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 sigma 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.