Unusually Short-Lived Solvent-Dependent Excited State in a Half-Sandwich Ru(II) Complex Induced by Low-Lying 3 MC States.

A ruthenium complex with a half-sandwich geometry ([(p-cymene)Ru(Cl)(curcuminoid)]) was synthesized, characterized, and investigated regarding its ultrafast photophysics. These photophysical investigations of the complex revealed a weak and short-lived emission from the initially populated 1 MLCT state and solvent-dependent photoinduced dynamics, where the secondarily populated 3 MC state is stabilized by nonpolar solvents. Overall the decay of the 3 dd-MC state to the ground state is completed within picoseconds. This short excited-state lifetime is in stark contrast to the typically observed long-lived 3 MLCT states with lifetimes of nanoseconds or microseconds in unstrained, octahedral ruthenium complexes but is in good agreement with the findings for distorted octahedral complexes. This is pointing to the half-sandwich geometry as a new and easy approach to study these otherwise often concealed dd states.