Isomerization in Photochromic Ruthenium Sulfoxide Complexes

The spectroscopic properties of photochromic ruthenium sulfoxide complexes are reviewed. The mode of action is associated with an excited state S→O isomerization triggered by light. These complexes feature large, positive Ru 3+/2+ reduction potentials indicative of stabilization of the Ru dπ orbital set. In addition, these compounds feature large quantum yields of isomerization. In aggregate, the data argue against a promoting role for the LF states and suggest that isomerization occurs from the CT potential energy surface. Picosecond transient absorption experiments indicate a change in the isomerization mechanism between mondentate sulfoxide complexes and chelating sulfoxide complexes. These results as well as potential energy diagrams for certain complexes are discussed.