Guest Alignment and Defect Formation during Pore Filling in Metal–Organic Framework Films

The degree of pore filling is an important parameter for defining guest@MOF properties in applications including electronics, optics, and gas separation. However, the interplay of key aspects of host–guest interactions, such as a quantitative description of the guest alignment or the structural integrity of the host as function of pore filling are yet to be determined. Polarisation‐dependent infrared spectroscopy in attenuated total reflection configuration combined with gas sorption allowed to simultaneously study the orientation of the guest molecule and structural changes of the MOF framework during the pore filling process. Thereby we found, that initially randomly oriented guest molecules align with increasing pore filling during adsorption from the gas phase. At the same time, the framework itself undergoes a reversible, guest molecule‐dependent rotation of the aromatic linker and a linker detachment process, which induce defects. Guest@MOF functionalities are strongly influenced by the degree of pore filling, the orientation of the guest as well as by structural changes of the host. We report a correlative study of these host–guest interactions as a function of the pore filling using combined polarisation‐dependent ATR‐FTIR spectroscopy and gas sorption.