Photo-induced reverse valence tautomerism in a metastable Co compound

In our preceding paper, we have reported that a Co complex, [CoIII-LS(tmeda)(3,5-DBSQ)(3,5-DBCat)]·0.5C6H5CH3, exhibits a photo-induced valence tautomerism. The photo-induced metastable state, [CoII-HS(tmeda)(3,5-DBSQ)2]·0.5C6H5CH3, has a back electron transfer band from CoII-HS to 3,5-DBSQ at around 800 nm, indicating that the valence tautomerism should be photo-reversible. In fact, we have found that the metastable state could be photo-pumped back to the original state by exciting the back electron transfer band. The process can be expressed as [CoII-HS(tmeda)(3,5-DBSQ)2]·0.5C6H5CH3(metastable state)→[CoIII-LS(tmeda)(3,5-DBSQ)(3,5-DBCat)]·0.5C6H5CH3 (ground state).