Structure and dynamics of solvent shells around photoexcited metal complexes

Understanding the geometry, energetics and dynamics of solvated transition metal (TM) compounds is decisive in characterizing and optimizing their function. Here, we demonstrate that it is possible to quantify the structural dynamics of solvated [Ru(II)(bpy)3], an important TM-complex for solar-energy harvesting research, by using state-of-the art force fields together with molecular simulations. Electronic excitation to [Ru(III)(bpy)3] leads to a nonequilibrium system in which excess energy is redistributed to the surrounding solvent following a cascade of dynamical effects that can be characterized by the simulations. The study reveals that the structure of the surrounding solvent relaxes towards the equilibrium on a sub-picosecond to a few-picosecond time scale. Analysis of solvent residence and rotational reorientation times during relaxation demonstrates increased dynamics in the inner solvation sphere on the picosecond time scale. Energy transfer to the solvent occurs on different time scales for the different degrees of freedom which range from a few hundred fs to several picoseconds.