Switchable Fluorescence of a Three-Dimensional Coordination Polymer Based on Reversible Single-Crystal to Single-Crystal Photoreaction

Photoreactive coordination polymers (CPs) are vital crystalline platforms for precise control of customized solid-state photochemistry. Benefiting from their ordered crystalline frameworks and photoresponsive active sites, these CPs can be developed into photocontrolled smart materials, supporting the rational design and manufacture of high-performance optoelectronic and optical devices. In this work, a three-dimensional (3D) photoreactive CP, namely {[Cd(1,4-ndc)(3,3′-dpe)]·H 2 O} n ( 1 ), was successfully prepared via a hydrothermal strategy, utilizing Cd(NO 3 ) 2 ·4H 2 O, 1,4-naphthalenedicarboxylic acid (1,4-H 2 ndc) and 1,2-di(pyridin-3-yl)ethene (3,3′-dpe) as the initial reaction precursors. Under the irradiation of 365 nm UV light, 1 undergoes a [2 + 2] photocycloaddition reaction and yields a new 3D CP {[Cd(1,4-ndc)(3,3′-tpcb) 0.5 ]·0.5H 2 O} n ( 1a, 3,3′-tpcb= 1,2,3,4-tetra(pyridin-3-yl)cyclobutane) in a single-crystal to single-crystal (SCSC) manner. Upon exposure to 254 nm UV light, 1a can undergo a reversible cycloreversion reaction and restore the original structure of 1 . The reversible phototriggered cycloaddition–cycloreversion cycling between 1 and 1a is accompanied by distinct fluorescence emission characteristics, endowing the material with interesting photoswitchable fluorescence performance. The characteristics of the CP make it highly promising for widespread application in advanced functional fields such as reversible optical information storage, high-security optical anticounterfeiting and high-sensitivity fluorescence sensing.