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.

铜基金属有机框架（metal-organic framework，MOF）HKUST-1可将有机分子吸附至其孔道之中。当负载富电子低聚噻吩时，所得体系可在加热条件下引发氧化聚合反应，且无需额外添加氧化剂或催化剂。该反应在非氧化还原活性MOF MIL-100(Al)中未被观测到。我们通过光学显微与纳米级显微技术、振动光谱、紫外-可见光谱（UV–vis spectroscopy）、X射线光电子能谱（X-ray photoelectron spectroscopy）、氮气吸附分析以及热重分析/残余气体分析对该复合材料进行了表征。未取代的低聚噻吩可在MOF孔道内发生聚合，而3,4-乙撑二氧噻吩（3,4-ethylenedioxythiophene）则会在MOF表面形成涂层。孔道内包埋共轭聚合物掺杂剂的MOF复合材料，其电子结构会发生显著变化。我们通过结合单体的HKUST-1模型体系的含时密度泛函理论计算，对观测到的反应活性进行了合理化阐释，并提出了基于配体到金属电荷转移态的引发机制。