Stepwise Structural Transformations of Coordination Polymers Caused by Ligands Replacements and Solid-State Photoreaction

The structural transformations of coordination polymers not only contribute to structural diversity but also provide design strategies at the molecular level for developing a new generation of smart materials. In this work, a photoinert olefin-containing coordination chain {[Zn(H₂O)(5-NO₂-1,3-BDC)(3,3′-dpe)]₂·H₂O}_n (1) was prepared by the hydrothermal reaction between Zn(NO₃)₂·6H₂O, 1,2-di(pyridin-3-yl)ethene (3,3′-dpe), and 5-nitro-1,3-benzenedicarboxylic acid (5-NO₂-1,3-H₂BDC). After replacing the 5-NO₂-1,3-H₂BDC ligand in the solution of 1 with 5-methyl-1,3-benzenedicarboxylic acid (5-Me-1,3-H₂BDC), a unique two-dimensional photoreactive coordination network [Zn(5-Me-1,3-BDC)(3,3′-dpe)]_n (2) was formed. When exposed to UV light, 2 can undergo a [2 + 2] photocycloaddition reaction to produce [Zn(5-Me-1,3-BDC)(rctt-3,3′-tpcb)_0.5]_n (3, 3,3′-tpcb = 1,2,3,4-tetra(pyridin-3-yl)cyclobutane) via single-crystal-to-single-crystal (SCSC) transformation. By replacing the 5-Me-1,3-BDC ligand in the solution of 3 with 5-NO₂-1,3-H₂BDC, a three-dimensional framework of {[Zn₂(5-NO₂-1,3-BDC)₂(rtct-3,3′-tpcb)]·2H₂O}_n (4) can be obtained. Accompanied by the in situ solid-state photoreaction, 2 exhibits intriguing photocontrolled fluorescence behavior, making it a promising smart material for applications in fluorescence sensors, super-resolution imaging, and optical anticounterfeiting.