Photochromic Reversible Substitution Reaction of Tridentate Schiff Base-Ruthenium(II) Complexes

In acetonitrile, the chloro ligands of [RuCl2(ppb-etol)(PPh3)] (1, ppb-etol = N-(2-diphenylphosphinobenzilidene)-2-hydroxyethylamine) are substituted with the solvent molecules to yield an equilibrium mixture of [RuCl(CH3CN)(ppb-etol)(PPh3)]Cl (2) and [Ru(CH3CN)2(ppb-etol)(PPh3)]Cl2 (3) at 50°C in the dark. The reaction is accompanied by a color change from orange to yellow. Upon irradiation of UV-vis light, the color of the solution reverts to orange, and complexes 2 and 3 are converted again into complex 1. The color change can be made repeatedly and a reversible photochromic reaction system is constructed.