Two-Step Photon Absorption Driving the Chemical Reaction in the Model Ruthenium Nitrosyl System [Ru(py)4Cl(NO)](PF6)2·1/2H2O

International audienceVarious systems contg. the [ML5NO] mol., where M = Fe, Ru, ... and L = F, Cl, ..., exhibit switching under continuous light (CW) irradn. between the ground-state nitrosyl (GS), isonitrosyl (MSI), and side-on (MSII) configurations. The metastable populations, however, are often limited to a few percent. The [Ru(py)4Cl(NO)](PF6)2·1/2H2O system is thus a remarkable model compd. as the GS to MSI transformation is nearly complete in a single crystal. A predominant two-step photon absorption process during GS to MSI switching under blue light is revealed by visible absorption spectroscopy, although a low concn. of the transient species hinders the detn. of this process by the structural signature. During the depopulation of MSI, both two-step and direct processes are evidenced under red CW irradn. Different intermediate visible spectra revealing transient species during GS to MSI and the reverse photochem. processes are discussed in relation to MSII properties