Revealing Metal-Node-Dependent Intralayer Conjugation and Thickness-Dependent Interlayer Interactions in Photoconductive MOFs

Triphenylene (TP) based 2-dimensional (2D) metal-organic frameworks (MOFs) have attracted growing interest as photoconductive materials for sensing, photo(electro)catalysis, energy storage, and optoelectronic applications. However, the fundamental understanding of the factors that govern charge transport mechanisms in these materials remains poorly understood. In this work, we combine multiple spectroscopic techniques, including steady state X-ray absorption and UV-Visible-NIR absorption spectroscopy, transient absorption spectroscopy, and first-principles calculations, to examine the origins of charge transport behaviors in hexahydroxytriphenylene (HHTP) based MOFs. We found that the metal-to-ligand charge-transfer band is governed by the identity of the metal node, highlighting the important role of metal-ligand d-π interactions, whereas the near-infrared absorption band depends strongly on film thickness, reflecting the contribution of interlayer π-π interactions. Our findings identify two distinct strategies for tuning charge transport mechanisms in these emerging materials and provide new mechanistic insights to guide the rational design of HHTP-based MOFs for practical device applications.