A Comparison of Partial Atomic Charges for Electronically Excited States

Partial atomic charges are a useful and intuitive concept for understanding molecular properties and chemical reaction mechanisms, showing how changes in molecular geometry can affect the flow of electronic charge within a molecule. However, the use of partial atomic charges remains relatively uncommon in the characterization of excited-state electronic structure. Here, we show how well-established partial atomic charge methods perform for interatomic, intermolecular, and interbond electron transfer in electronically excited states. Our results demonstrate the utility of real-space partial atomic charges for interpreting the electronic structures that arise in excited-state processes. Furthermore, we show how this analysis can be used to demonstrate that analogous electronic structures arise near photochemically relevant conical intersection regions for several conjugated polyenes. On the basis of our analysis, we find that charges computed using the iterative Hirshfeld approach provide results which are consistent with chemical intuition and are transferable between homologous molecular systems.