Controllable Fluorescence Switching of a Coordination Chain Based on the Photoinduced Single-Crystal-to-Single-Crystal Reversible Transformation of a <i>syn</i>-[2.2]Metacyclophane

The observation of a reversible chemical transformation corresponding to an external stimulus in the solid state is intriguing in the exploration of smart materials, which can potentially be applied in molecular machines, molecular switches, sensors, and data storage devices. The solid-state photodimerization reaction of 1,3-bis­[2-(4-pyridyl)­ethenyl]­benzene (1,3-bpeb) in a one-dimensional coordination polymer {[Cd<sub>2</sub>(1,3-bpeb)<sub>2</sub>­(4-FBA)<sub>4</sub>]·H<sub>2</sub>O}<sub><i>n</i></sub> (4-FBA = 4-fluorobenzoate) with 365 nm UV light afforded <i>syn</i>-tetrakis­(4-pyridyl)-1,2,9,10-diethano­[2.2]­metacyclophane (<i>syn</i>-tpmcp) in quantitative yield via a single-crystal-to-single-crystal (SCSC) transformation. Upon irradiation with 254 nm UV light, an SCSC conversion from <i>syn</i>-tpmcp to 1,3-bpeb was also achieved in quantitative yield within the <i>syn</i>-tpmcp-supported coordination polymer {[Cd<sub>2</sub>(<i>syn</i>-tpmcp)­(4-FBA)<sub>4</sub>]·H<sub>2</sub>O}<i><sub>n</sub></i>. In particular, accompanied by the reversible transformation between 1,3-bpeb and <i>syn</i>-tpmcp, the coordination chain exhibits photocontrollable fluorescence-switching behavior, which makes this intelligent material an appealing candidate for practical applications.