Reversible Transformations of Topology and Partial Interpenetrations in Metal-Organic Frameworks Triggered by Solid-State Photo/Thermal Reactions

Abstract

Reversible control of topology and partial-interpenetration transformations in metal-organic frameworks (MOFs) is vital for customizing their functional properties, but this area has long been insufficiently explored. Herein, we report the reversible regulation of both topology and partial-interpenetration in photo/thermal-responsive MOFs, focusing on the two-interpenetrated [Zn(L₁)(H₂O)]_n (L₁ = biphenylethene-4,4'-dicarboxylic acid). Through solid-state [2+2] cycloaddition reactions, this MOF was transformed into partially interpenetrated [Zn(L₁)_x(L₂)_1–x(H₂O)]_n (x represents the molar ratios of organic linkers) and non-interpenetrated [Zn(L₂)(H₂O)]_n with different topology (L₂ = 4,4',4”,4”'-(cyclobutane-1,2,3,4-tetrayl)tetrabenzoic acid, a cyclobutane derivative of L₁), and thermal treatment triggered reverse ring-opening to recover the original structure. These transformations were verified and visualized using single-crystal X-ray diffraction, synchrotron infrared spectroscopy, and other techniques. By introducing a third organic linker L₃ (azobenzene-4,4'-dicarboxylic acid), we synthesized multivariate MOFs (MTV-MOFs, [Zn(L₁)_x(L₃)_1–x(H₂O)]_n) and precisely tuned their structural transformations by adjusting the ratio of the two linkers. By leveraging the inherent photoactivity of these MOFs and the photoexcited electrons generated during these structural transformations, they can be used to detect reductive molecules such as glucose. Their photocurrent-based glucose detection exhibited a high sensitivity of up to 780 μA·M^–1·cm^–2. This work enriches the structural diversity of MOFs and enhances their potential applications in adsorption and molecular recognition.