Photophysical Properties of Homometallic Ruthenium(II) and Osmium(II) Complexes with a Bis(dipyridophenazine) Bridging Ligand. From Pico- to Microsecond Time Resolution

摘要

The photophysical properties of [Ru-bidppz-Ru]~(4+), [Os-bidppz-Os]~(4+), and the bridging ligand bidppz (bidppz = 1,1'-dipyrido[3,2-a:2',3'-c]phenazin-1,1'-yldipyrido[3,2-a:2',3'-c]phenazine) are investigated. Time-resolved spectroscopic studies were performed on (sub)pico- to microsecond time scales, offering insight into the excited states responsible for the photophysical behavior of the two complexes in different solvents. In particular, [Ru-bidppz-Ru]~(4+) shows a long excited-state lifetime, 9.7 μs, in deaerated dichloromethane solution, that becomes much shorter (360 ns) in deaerated butyronitrile. The solvent plays a crucial role for the spectroscopic properties of this complex, since the energy of the triplet metal-to-ligand charge-transfer (~3MLCT) excited state is influenced by the polarity of the medium. (Sub)picosecond transient absorption spectra in dichloromethane indicate thermal population of the long-lived triplet intraligand (~3IL) sate of the bridging ligand from the lower lying ~3MLCT state. For [Os-bidppz-Os]~(4+) in dichloromethane the ~3MLCT state lies lower in energy and no interaction of this state with the ~3IL state of the bridging ligand is observed.