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

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.