Directional Charge Transport via Interlayer Electronic Coupling Enhances Photocatalysis in Covalent Organic Frameworks

Abstract

The design of efficient photocatalysts requires control over both exciton dissociation and the subsequent transport of charge carriers. Donor–acceptor two-dimensional covalent organic frameworks (COFs) are widely used to promote charge separation, but the role of directional charge transport in these layered materials is still not well understood. Here, we combine photophysical characterization and time-dependent density functional theory calculations to study three TAPD-based COFs for photocatalytic H2O2 production via oxygen reduction. All materials show efficient in-plane donor–acceptor charge transfer with similar exciton dissociation behavior. At the same time, clear differences appear in their charge transport properties. The calculations indicate that electrons move preferentially along the stacking direction, while holes remain more delocalized within the COF plane. This anisotropic transport is most pronounced in the COFs where stronger interlayer coupling favors the formation of interlayer charge-transfer states, as observed in transient absorption measurements. These states allow electrons and holes to separate over adjacent layers, which reduces recombination losses and corroborates the observed differences in photocatalytic activity. Our results indicate that directional interlayer charge transport, rather than local donor–acceptor charge separation alone, is an important factor in determining photocatalytic performance in COFs.