Rendering High Surface Area, Mesoporous Metal-Organic Frameworks Electronically Conductive.

Abstract

We report the design and synthesis of a metal-organic framework (MOF)-polythiophene composite that has comparable electronic conductivity to reported conductive 3-D MOFs, but with display and retention of high porosity, including mesoporosity. A robust zirconium MOF, NU-1000, was rendered electronically conductive by first incorporating, via solvent-assisted ligand incorporation (SALI), a carefully designed pentathiophene derivative at a density of one pentamer per hexa-zirconium node. Using a cast film of the intermediate composite (termed pentaSALI) on conductive glass, the incorporated oligothiophene was electrochemically polymerized to yield the conductive composite, Epoly. Depending on the doping level of the polythiophene in the composite, it can be tuned from an insulating state to a semiconduting state with conductivity of 1.3 × 10-7 (S cm-1), which is comparable to values reported for 3-D conductive MOFs. The porosity of the thin-film MOF-polythiophene composite was assessed using decane vapor uptake as determined by quartz crystal microgravimetry (QCM). The results indicate a porosity (pore volume) for Epoly essentially identical to that of bulk pentaSALI, and ∼74% of that of unmodified NU-1000. PentaSALI, and by inference Epoly, displays both micro- and mesoporosity, and features a BET surface area of nearly 1,600 m2·g-1, i.e., substantially larger than yet reported for any other electronically conductive MOF.