Structural determinants of photo-accumulated charge storage in poly-heptazine imides

<h2>Summary</h2> Integrating solar energy capture and storage directly into an electrical form in a single material presents a promising strategy to address the intermittency aspect of solar power. In recent years, potassium poly-heptazine imide (K-PHI) has been showcased as having a unique ability to photo-accumulate charge, which can subsequently be utilized for dark photocatalysis and solar battery applications. However, understanding the underlying chemical and structural factors governing photo-accumulated charge (PAC) formation in K-PHI remains unclear. Here, we report a study that delves into the structural features and identifies the chemical groups that govern the formation of the PAC state in K-PHI through a combination of <i>ex situ</i> and <i>in situ</i> spectroscopic studies. Additionally, the findings suggest a donor-acceptor behavior in this extended disordered K-PHI polymer, which allows for a prolonged retention of photo-induced radicals in acceptor moieties. Importantly, this work opens avenues for exploring more precise donor-acceptor systems for photo-induced charge storage, potentially advancing materials for solar rechargeable batteries and dark photocatalytic applications.