Light-induced linkage isomerization of photochromic [Ru(bpy)2(R-OSO)]+ compounds

Ruthenium sulfoxides exhibit light-induced linkage isomerization of the SO-bond with remarkable photosensitivity S=(0.25±0.03) Ws cm-1 and extended lifetimes of the related metastable states in the order of 104 s. The isomerization is accompanied with tremendous changes of the optical extinction up to 9350 cm-1 mol-1 thus enabling the study of linkage isomerization by means of time-resolved optical spectroscopy. Here, the influence of ligand substitution is studied via inspection of the photosensitivity and the generation and relaxation dynamics of the photochromic response as a function of temperature (pump at λ=405 nm, probe at λ=532 nm). The spectra of the modified compounds, where ligands R=Bn, BnCl, and BnMe were attached to OSO, were compared with the reference system [Ru(bpy)2(OSO)]+. It turns out, that the new ligands affect the absorption features and the photosensitivity of the system only slightly. In contrast, a strong influence of the thermal relaxation of the metastable states is uncovered. Remarkably, the influence on the frequency factors is much more pronounced than on the activation energies achieved by Arrhenius' law.