Reversible trans ⇌ cis photoisomerizations of [Re(CO)3(ph2phen)(stpyCN)]+ towards molecular machines

Abstract

In our search for light powered molecular devices, a novel fac-[Re(CO)₃(ph₂phen)(trans-stpyCN)]⁺ complex was synthesized to show switchable trans–cis configurations of the coordinated stpyCN ligand through efficient and reversible photoassisted isomerizations. Controlled photolyses of acetonitrile solutions led to spectral changes ascribed to reversible trans ⇌ cis photoisomerization processes. A remarkable quantum yield for the back cis-to-trans isomerization was obtained, with the same magnitude of the trans-to-cis photoprocess, and curiously, both trans- and cis-isomers are emissive at room temperature. Photochemical and photophysical characterization studies for fac-[Re(CO)₃(ph₂phen)(stpyCN)]⁺ provided insights into the isomerization and emissive light-driven pathways that are resulted from the interactions between the close-lying intraligand and charge transfer states. The reversible cis–trans photoisomerization has potential to be exploited as light-powered molecular motors and geometry regulators in molecular machines.