Reversible Single-Crystal-to-Single-Crystal Transformation of a Coordination Polymer through Solar-Switchable Cycloaddition and Cycloreversion Reaction.

Reversible covalent reactions within crystalline complexes are powerful tools for the design and developing of new generation of reusable smart materials. In this work, a unique photoreactive olefin-containing metal-organic coordination polymer [Ag ₂ (2,3-ppe) ₂ (1,3-bdc)] _n ( 1 ) was prepared by the hydrothermal reaction between AgNO ₃ , 1-(2-pyridyl)-2-(3-pyridyl)ethylene (2,3-ppe), and 1,3-benzenedicarboxylic acid (1,3-H ₂ bdc). When exposed to sunlight, 1 can undergo single-crystal-to-single-crystal (SCSC) transformation to form [Ag ₂ (dpdpcb)(1,3-bdc)] _n ( 1a , dpdpcb = 1,3-di(2-pyridyl)-2,4-di(3-pyridyl)cyclobutane) through a [2 + 2] cycloaddition reaction. 1a can regenerate into 1 via the cycloreversion reaction based on the thermal effect of sunlight. Such a metal-organic complex exhibits interesting fluorescence switching behavior during the unprecedented fully solar-controlled reversible SCSC reaction, which makes it possible to be applied to the fields of optical memory storage and anti-counterfeiting.