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}<i>_n</i> (<b>1</b>) 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 <b>1</b> 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)]<i>_n</i> (<b>2</b>) was formed. When exposed to UV light, <b>2</b> can undergo a [2 + 2] photocycloaddition reaction to produce [Zn(5-Me-1,3-BDC)(<i>rctt</i>-3,3'-tpcb)_0.5]<i>_n</i> (<b>3</b>, 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 <b>3</b> with 5-NO₂-1,3-H₂BDC, a three-dimensional framework of {[Zn₂(5-NO₂-1,3-BDC)₂(<i>rtct</i>-3,3'-tpcb)]·2H₂O}<i>_n</i> (<b>4</b>) can be obtained. Accompanied by the in situ solid-state photoreaction, <b>2</b> exhibits intriguing photocontrolled fluorescence behavior, making it a promising smart material for applications in fluorescence sensors, super-resolution imaging, and optical anticounterfeiting.