Ruthenium Polypyridyl Complexes Hopping at Anionic Lipid Bilayers through a Supramolecular Bond Sensitive to Visible Light

The new ruthenium complex [Ru(terpy)(dcbpy)(Hmte)](PF 6 ) 2 ([ 2 ](PF 6 ) 2 ; dcbpy=6,6′‐dichloro‐2,2′‐bipyridine, terpy=2,2′;6′,2“‐terpyridine, Hmte=2‐(methylthio)ethanol) was synthesized. In the crystal structure, this complex is highly distorted, revealing steric congestion between dcbpy and Hmte. In water, [ 2 ] 2+ forms spontaneously by reacting Hmte and the aqua complex [Ru(terpy)(dcbpy)(OH 2 )] 2+ ([ 1 ] 2+ ), with a second‐order rate constant of 0.025 s −1   M −1 at 25 °C. In the dark, the RuS bond of [ 2 ] 2+ is thermally unstable and partially hydrolyzes; in fact, [ 1 ] 2+ and [ 2 ] 2+ are in an equilibrium characterized by an equilibrium constant K of 151  M −1 . When exposed to visible light, the RuS bond is selectively broken to release [ 1 ] 2+ , that is, the equilibrium is shifted by visible‐light irradiation. The light‐induced equilibrium shifts were repeated four times without major signs of degradation; the RuS coordination bond in [ 2 ] 2+ can be described as a robust, light‐sensitive, supramolecular bond in water. To demonstrate the potential of this system in supramolecular chemistry, a new thioether–cholesterol conjugate ( 4 ), which inserts into lipid bilayers through its cholesterol moiety and coordinates to ruthenium through its sulfur atom, was synthesized. Thioether‐functionalized, anionic, dimyristoylphosphatidylglycerol (DMPG), lipid vesicles, to which aqua complex [ 1 ] 2+ efficiently coordinates, were prepared. Upon exposure of the Ru‐decorated vesicles to visible light, the RuS bond is selectively broken, thus releasing [ 1 ] 2+ that stays at the water‐bilayer interface. When the light is switched off, the metal complex spontaneously coordinates back to the membrane‐embedded thioether ligands without a need to heat the system. This process was repeated four times at 35 °C, thus achieving light‐triggered hopping of the metal complex at the water‐bilayer interface.