Control of structural flexibility of layered-pillared metal-organic frameworks anchored at surfaces

Suttipong Wannapaiboon,Roland A Fischer,Anna Lisa Semrau,Inke Hante,Min Tu,Konstantin Epp,Samuel J Baxter,Gregor Kieslich,Christian Sternemann,Andreas Schneemann,Michael Paulus

doi:10.1038/s41467-018-08285-5

Abstract

Flexible metal-organic frameworks (MOFs) are structurally flexible, porous, crystalline solids that show a structural transition in response to a stimulus. If MOF-based solid-state and microelectronic devices are to be capable of leveraging such structural flexibility, then the integration of MOF thin films into a device configuration is crucial. Here we report the targeted and precise anchoring of Cu-based alkylether-functionalised layered-pillared MOF crystallites onto substrates via stepwise liquid-phase epitaxy. The structural transformation during methanol sorption is monitored by in-situ grazing incidence X-ray diffraction. Interestingly, spatially-controlled anchoring of the flexible MOFs on the surface induces a distinct structural responsiveness which is different from the bulk powder and can be systematically controlled by varying the crystallite characteristics, for instance dimensions and orientation. This fundamental understanding of thin-film flexibility is of paramount importance for the rational design of MOF-based devices utilising the structural flexibility in specific applications such as selective sensors.

Highlights

Flexible metal-organic frameworks (MOFs) are structurally flexible, porous, crystalline solids that show a structural transition in response to a stimulus
We employed for the first time the stepwise liquid-phase epitaxy (LPE) process to anchor a nanolayer of flexible layered-pillared MOF crystallites onto SAMfunctionalised quartz crystal microbalance (QCM) substrates
The crystallite dimensions have a distinct effect on the structural dynamics

Summary

Introduction

Flexible metal-organic frameworks (MOFs) are structurally flexible, porous, crystalline solids that show a structural transition in response to a stimulus. Spatially-controlled anchoring of the flexible MOFs on the surface induces a distinct structural responsiveness which is different from the bulk powder and can be systematically controlled by varying the crystallite characteristics, for instance dimensions and orientation This fundamental understanding of thin-film flexibility is of paramount importance for the rational design of MOF-based devices utilising the structural flexibility in specific applications such as selective sensors. The specific design of MOF components to control attractive forces used for assembling the porous scaffolds can initiate structural dynamics in some MOFs (named flexible MOFs or soft porous crystals (SPCs))[10,15,16,17,18] Depending on their characteristic features, SPCs can undergo reversible phase transitions in various flexible modes (i.e., breathing[19], swelling[20], ligand rotation[21], subnetwork displacement22,23) upon external stimuli such as guest sorption, temperature change, light and mechanical pressure[15,16]. The discovery of highly-responsive MOFs highlights the potential applications for selective gas storage[24,25,26], effective gas separation[27], controlled drug release[28] and smart sensors[29]

Methods

Results

Conclusion