Photo-reversible valence tautomerism in a Co compound

Photo-illumination effects have been measured for the compound [CoIII-LS(tmpda)(3,6-DBSQ)(3,6-DBCat)]. When the aforementioned compound was illuminated at 5 K, the magnetization value increased from mu(eff) = 1.87 to 2.03 mu(B). The absorption spectra after illumination show that the absorption band at around 730 nm, which is characteristic of the [CoII-HS(tmpda)(3,6-DBSQ)(2)] state, increased in intensity and that the charge transfer band from 3,6-DBCat to 3,6-DBSQ at 2500 nm was reduced in intensity. IR spectra show that the C-O stretching peak at 1279 cm(-1) is decreased in intensity. These results confirm that a photoinduced intra-molecular electron transfer, [CoIII-LS(tmpda)(3,6-DBSQ)(3,6-DBCat)]--> [CoII-HS(tmpda)(3,6-DBSQ)(2)], was induced. The lifetime of the metastable state at 5 K was 15 min. Furthermore, it was found that reverse valence tautomerism can be induced by exciting the CoII-HS to 3,6-DBSQ charge transfer band in metastable [CoII-HS(trnpda)(3,6-DBSQ)(2)].