Chemical Regulation of Attosecond Charge Migration

Charge migration (CM) is an attosecond process where a localized electron hole travels across a molecule in a coherent manner at time scales faster than nuclear motion. Despite much recent interest, many questions remain concerning the relationship between a molecule's chemical functionalization and the CM modes it supports. Understanding these structure/property relationships is critical for identifying molecules for attosecond experiments. In this work, we use time-dependent density functional theory simulations to elucidate the modes of attosecond charge migration (CM) in a range of functionalized conjugated linear and ring-shaped molecules. Here, the halogen acts as a site for initial hole creation via strong-field ionization, and distant electron/donating groups act as hole acceptors. We observe that for linear chains, the CM speed (∼4 Å/fs) is largely independent of molecule length, but is lower for triple-bonded versus double-bonded molecules. Additionally, as the halogen atomic number increases, the hole travels in a more particle-like manner as it moves across the molecule. Finally, the "hole affinity" of a functional group increases with the electron donating strength, leading to a Hammett-like series for CM. Together, these results form a set of heuristics that will be useful for guiding and interpreting identifying molecules for future charge migration experiments.