Switching the Proton Conduction in MOFs by Light

Smart MOF materials can be prepared by incorporation of stimuli-responsive molecules, changing their properties upon exposure to external stimulus. Stimuli such as like temperature, pH or light attract particular interest, whereat light enables highest spatial resolution and fast response over long distances. One of the most frequently investigated photochromic molecule is azobenzene, which can isomerize from its non-polar trans state to the polar cis state. While plain azobenzene requires UV light for its isomerization, fluorine-functionalized molecules enable the reversible trans-cis switching with visible light only, avoiding UV. By incorporating fluorinated azobenzene as side groups in the MOF structure, the ability for photoisomerization is preserved and integrates photoswitchable, smart properties to the MOF material. In that way, the pore structure and the size of the pore opening as well as the polarity of the pore environment can be photo-switched. This results in a remote-control of the interaction of the MOF material with the guest molecules in the pores, controlling, e.g., the adsorption and diffusion properties. This can be used for membranes with remote-controllable permeation and separation factors. ... mehrMoreover, the control over the host-guest interaction results in the remote switching of the proton-conduction properties. In this presentation, the photoswitching of the proton-conduction and further properties of smart MOFs with azobenzene side groups is discussed.