Transforming an insulating metal–organic framework into electrically conducting metal–organic framework⊃conducting polymer composites

Abstract

Owing to their diverse potentials to help advance modern electronics and energy technologies, electrically conducting metal–organic frameworks (MOFs) have emerged as one of the most coveted functional materials within the past decade. The key to developing electrically conducting MOFs is to equip them with mobile charge carriers and facilitate long-range charge movement. Circumventing the challenges and unpredictability associated with the construction of intrinsically conducting MOFs, herein, we have converted a structurally robust and porous but intrinsically insulating Zn-dpzNDI MOF based on an electron deficient dipyrazolate-naphthalenediimide (dpzNDI) ligand into electrically conducting MOF⊃conducting-polymer (MOF⊃CP) composites via oxidative polymerization of preloaded redox-active 3,4-ethylenedioxythiophene (EDOT) and pyrrole (Py) monomers to corresponding PEDOT and PPy polymers, which are well-known hole-transporters. After monomer loading and in-situ polymerization, the resulting MOF⊃CP composites remained crystalline but became less porous, suggesting that the amorphous CP chains were mostly confined to the MOF cavities. The presence of CPs was confirmed by infra-red (IR), diffuse-reflectance UV–Vis–NIR and STEM-EDX analyses. Whereas the pristine MOF had immeasurably low conductivity (σ < 10−12 S/m), the MOF⊃PEDOT and MOF⊃PPy composites displayed significantly higher electrical conductivity: 1.8 × 10−5 and 2.5 × 10−3 S/m, respectively. Thus, we have transformed an intrinsically insulating MOF into electrically conducting MOF⊃CP via in-situ oxidative polymerization of electron-rich monomers, a versatile strategy that could be adopted to engineer this much coveted but elusive electronic property practically in any porous MOFs.