Deciphering the substituent effect on charge transport in solid-state framework lattice

Translating molecular design principles into predictive rules for extended solid-state materials remains a fundamental challenge in chemistry. The substituent effect, a cornerstone of molecular chemistry, is well understood at the molecular level yet often becomes ambiguous in solids where collective electronic interactions dominate. Here, we establish a quantitative framework to elucidate how substituent effect govern charge transport in extended crystalline materials using a family of eight isoreticular conductive metal-organic frameworks constructed from hexahydroxytriphenylene ligands bearing substituents with varied electronic and steric characteristics. Small electron-withdrawing groups are found to enhance carrier delocalization, reduce activation energies, and even shift the carrier from n- to p-type, whereas bulky electron-donating groups suppress charge transport. To unify the electronic and steric contributions from the substituents, we introduce a parameter, the harmonic substituent constant, that quantitatively correlates experimental charge transport parameters, establishing a conceptual bridge between classical molecular substituent theory and charge transport in extended solids.