Photo-induced reverse valence tautomerism in a metastable Co compound

;in our preceding paper. we have reported that a Co complex, [Co111-LS (tmeda) (3, 5-DBSQ) (3, 5-DBCat)] 0.5C(6)H(5)CH(3), exhibits a photo-induced valence tautomerism. The photo-induced metastable state, (Co11-HS (tmeda) (3,5-DBSQ)(2)]. 0.5C(6)H(5)CH(3). has a back electron transfer band from Co11-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 (Co11-HS(tmeda)(3, 5-DBSQ)(2)] (.) 0.5C(6)H(5)CH(3) (metastable state) - [Co111-LS(tmeda)(3, 5-DBSQ)(3, 5-DBCat)] (.) 0.5C(6)H(5) CH.; (ground state). (C) 2002 Published by Elsevier Science B.V.