Crystallographic Visualization of a Guest-Induced Solar-Driven Cycloaddition Reaction Based on a Recyclable Nonporous Coordination Polymer.

Stimuli-responsive solids with adjustable photophysical properties are particularly attractive because they can be used as smart materials in anticounterfeiting, information storage, holographic imaging, and other fields. Herein, we report a unique nonporous coordination polymer, {[Ag(3,3'-dpe)](2,2'-Hbpdc)}n (1; 3,3'-dpe = 1,2-dipyridin-3-ylethene and 2,2'-H2bpdc = 2,2'-biphenyldicarboxylic acid), that can convert to an extremely photoreactive compound, 1·H2O·MeCN (MeCN = acetonitrile), through guest capture. Upon irradiation of sunlight, 1·H2O·MeCN can transform to {[Ag(3,3'-tpcb)0.5](2,2'-Hbpdc)(H2O)(MeCN)}n (2·H2O·MeCN; 3,3'-tpcb = 1,2,3,4-tetrapyridin-3-ylcyclobutane). 2·H2O·MeCN can lose its solvent molecules to form 2 and further return to 1 at high temperature. Accompanied by direct visualization based on multistep single-crystal-to-single-crystal conversions, the recyclable crystalline solid exhibits remarkable fluorescence changes, which makes it a supramolecular switch for application in multiple anticounterfeiting.