A combined QM/MM and Classical Molecular Dynamics Study of [Ru(bpy)3]2+ in Water

The solvation of the Ru(bPy)(3) (bpy = 2,2'-bipyridyl) cation was studied by molecular dynamics simulations, using both a hybrid QM/MM Car-Parrinello scheme and a classical force field. The trajectory analysis reveals that the first solvation sphere consists of chains of H-bonded water molecules intercalating between the bpy ligands, which in turns induces an organization of the second solvation sphere. Comparison with a simple charged sphere model shows the influence of the geometry of the cation and its ligands on the surrounding water. A water residence time in the first solvation shell of Ru(bpy)(3) of 12.4 ps is computed, which is significantly larger than the value of 4.5 ps found in bulk water. On the other hand, due to the one-dimensional arrangement of hydrogen bonds, the dipole of the water molecules can easily reorient, providing a way to explain the fast solvent dependent relaxation dynamics observed following photoexcitation.