Tunable Charge Transport Properties Through Precise π-Stacking Modulation in Isostructural Porous Molecular...

Understanding the structure-property relationships in electrically conductive metal-organic frameworks (MOFs) is critical for their rational design toward practical applications. Since single crystals of MOFs with through-space conductive π-stacked columnar structures are relatively easy to obtain, their structures can be determined with high accuracy. However, elucidating those structure-property relationships without interference from carrier scattering and variations in carrier concentration remains challenging. Herein, we synthesized three isostructural porous molecular conductors (denoted as PMC-3) via electrocrystallization using a redox-active N,N'-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxdiimide (NDI-py) ligand and ZnX₂ (X = Cl, Br, I). Single crystals of PMC-3 exhibit high electrical conductivity (∼10^-3 S cm^-1), comparable to the highest values reported for NDI-based crystalline materials. Moreover, PMC-3 serves as a model system for probing structure-property relationships in through-space conductive MOFs, offering three key advantages. First, the absence of counterions, eliminating carrier scattering; second, identical carrier concentrations across the series, allowing isolation of the effects of π-stacking geometry on transport properties; and third, tunable π-stacking geometries via halide ligand substitution. As a result, a linear correlation between the lattice parameter along the stacking axis and intrinsic charge transport properties is revealed, representing a significant advance in understanding charge transport in through-space conductive MOFs.