Photoisomerization Mechanism of Ruthenium Sulfoxide Complexes: Role of the Metal‐Centered Excited State in the Bond Rupture and Bond Construction Processes

Phototriggered intramolecular isomerization in a series of ruthenium sulfoxide complexes, [Ru(L)(tpy)(DMSO)] n + (where tpy=2,2’:6’,2’’‐terpyridine; DMSO=dimethyl sulfoxide; L=2,2’‐bipyridine (bpy), n =2; N , N , N ’, N ’‐tetramethylethylenediamine (tmen) n =2; picolinate (pic), n =1; acetylacetonate (acac), n =1; oxalate (ox), n =0; malonate (mal), n =0), was investigated theoretically. It is observed that the metal‐centered ligand field ( 3 MC) state plays an important role in the excited state S→O isomerization of the coordinated DMSO ligand. If the population of 3 MC S state is thermally accessible and no 3 MC O can be populated from this state, photoisomerization will be turned off because the 3 MC S excited state is expected to lead to fast radiationless decay back to the original 1 GS S ground state or photodecomposition along the Ru 2+ −S stretching coordinate. On the contrary, if the population of 3 MC S (or 3 MC O ) state is inaccessible, photoinduced S→O isomerization can proceed adiabatically on the potential energy surface of the metal‐to‐ligand charge transfer excited states ( 3 MLCT S → 3 MLCT O ). It is hoped that these results can provide valuable information for the excited state isomerization in photochromic d 6 transition‐metal complexes, which is both experimentally and intellectually challenging as a field of study.