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

Abstract

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 moleculedependent rotation of the aromatic linker and a linker detachment process, which induce defects.

Enhanced Orientation of Liquid Crystals Inside Micropores of Metal–Organic Frameworks Having Thermoresponsivity

“…The state of guest molecules in MOFs can be detected by IR spectroscopy. [21] Microscopic Raman and IR spectroscopy measurements were conducted for 5CB@IRMOF-9 to study the state of 5CB inside the MOFs, focusing on the peaks corresponding to the cyano groups (~2200 cm À 1 ). The Raman spectrum at r.t. of bulk-state 5CB showed a monomodal peak at 2226 cm À 1 , whereas 5CB@IRMOF-9 gave rise to three peaks at 2224, 2232, and 2266 cm À 1 at an intensity ratio of 67 %, 23 %, and 10 %, which can be attributed to a dimer state, a monomer state, and a zinc-coordinated state in the MOFs, respectively (Figure 3a).…”

Water sensitivity of heteroepitaxial Cu-MOF films: dissolution and re-crystallization of 3D-oriented MOF superstructures

“…Next, we analysed the chemical changes in the different MOF films by monitoring characteristic vibrational modes over time at the different RH values. We focused on the asymmetric and symmetric carboxylate stretching modes and compared to the pristine samples and previously reported spectra 23,24,42 to determine the coordination and protonation state of the carboxylic ligands. For the as-synthesized Cu 2 (BDC) 2 films, the asymmetric and symmetric carboxylate stretching modes were observed at 1579 cm −1 and 1398 cm −1 , respectively.…”

“…23 The resulting 3D-oriented MOF films, and more recently 3D-oriented micropatterns, exhibit anisotropy-derived properties, such as guest molecule alignment, polarized fluorescence, or polarization-dependent plasmon-resonance, among others. 19,21,24–26…”

Beyond the Conventional Limitation of Photocycloaddition Reaction in the Roomy Nanospace of a Metal–Organic Framework

“…The presence and absence of guest molecules alter the spatial arrangement of the reaction substrates integrated into the MOF backbone, giving different photoproducts . Additionally, internal voids of MOFs allow structural freedom of organic ligands to show dynamic motion, such as libration , and rotation. − From these characteristics, we anticipate that the locations of the reaction substrates in a flexible MOF nanospace can fluctuate thermally due to the displacement of the MOF backbone and/or the local mobility of the individual substrates. The expected molecular motion would temporarily allow them to approach each other, thus overcoming the conventional geometric limitations of topochemical reactions.…”