Polythiophene Doping of the Cu-Based Metal–Organic Framework (MOF) HKUST‑1 Using Innate MOF-Initiated Oxidative Polymerization

The copper-based
metal–organic framework (MOF) HKUST-1 adsorbs organic molecules
into its pores. When loaded with electron-rich oligothiophenes, the
resulting system reacts under heat to initiate oxidative polymerization
without the use of any other oxidant or catalyst. This reaction is
not observed in the non-redox-active MOF MIL-100­(Al). We have characterized
the composites by optical and nanoscale microscopy, vibrational and
UV–vis spectroscopy, X-ray photoelectron spectroscopy, N2 sorption analysis, and thermogravimetric analysis/residual
gas analysis. Unsubstituted oligothiophenes polymerize within MOF
pores, while 3,4-ethylenedioxythiophene forms a coating on the MOF
surface. MOF composites with conjugated polymer dopants trapped inside
their pores undergo profound shifts in the composite electronic structure.
Reasoning from time-dependent density functional theory calculations
of an HKUST-1 model system bound to monomers, we rationalize the observed
reactivity and propose an initiation mechanism based on a ligand-to-metal
charge-transfer state.