Stimuli-responsive behavior of mixed-linker Zr-based MOFs with molecular photoswitch backbones
Ardeshir Dadgar Yeganeh a, Simon Krause a
a Nanochemistry Department, Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
Proceedings of Dynamic Materials, Crystals and Phenomena Conference (DynaMIC23)
Fribourg, Switzerland, 2023 March 22nd - 24th
Organizers: Jovana Milic and Simon Krause
Poster, Ardeshir Dadgar Yeganeh, 024
Publication date: 15th February 2023

The investigation of Metal-Organic Frameworks (MOFs) structural responsive behavior to external stimuli such as light, temperature, and pressure has been growing over recent years.[1] Indeed, controlling the adsorption, transport, and release properties of gases and fluids in the framework materials by modulating their porosity via light provides exciting possibilities. Azobenzene is a molecular photoswitch that can go through light-activated E-Z isomerization and has been used in light-responsive materials.[2] Due to geometrical constraints, light-responsive properties of azobenzenes are subject to change when used as a linker in the MOF backbone. It has been shown that the photoswitching ability is either quelled as a result of the framework constraints or causes structural degradation when used in the framework backbone.[3, 4] However, by exploiting an additional external stimulus, the MOF's framework can undergo structural transition, as has been revealed before in the flexible DUT-163 material[5], where applying the light and adsorption stress in parallel, a cooperative gas release by a buckling contraction mechanism through the framework backbone was observed.

Herein, we report the synthesis of mixed-linker Zr-based UiO MOFs based on azobenzene dicarboxylic acid along with stilbene dicarboxylic acid. Stilbene and its carboxylic acid derivatives are also photoswitches that can undergo trans-cis interconversion through excitation with irradiation in different wavelengths than azobenzene, and together they can provide an interesting system to probe the possible isomerization or buckling of the constraint linker, and even possibly discover unknown alternative photoswitching pathways. The mixed-linker Zr-MOFs with different linker ratios were synthesized, and their structural features were investigated through various methods, including powder X-ray powder diffraction (PXRD) and scanning electron microscopy (SEM) as such. Future studies aim to determine whether molecular photoswitches can exhibit reversible or irreversible photoisomerization while being constrained in the framework and, if switching could not occur, what effects would arise regarding adsorption or mechanical pressure.

We would like to thank the Collaborative Research Center (CRC1333) and Carl-Zeiss-Stiftung for funding.

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