X-ray absorption spectroscopy as a probe of photo- and thermally induced valence tautomeric transition in a 1:1 cobalt-dioxolene complex.

The role of the cobalt ion in the entropy- and optically-driven valence tautomeric (VT) interconversion exhibited by the [Co(Me(2)tpa)(DTBdiox)](PF(6))C(6)H(5)CH(3) complex (Me(2)tpa = bis (6-methyl-(2-pyridylmethyl))(2-pyridylmethyl)amine, DBdiox = 3,5-ditertbutyl-dioxolene) is established by means of X-ray absorption spectroscopy (XAS). Analysis of the pre-edge features at 6 and 300 K in the Co K-edge XAS spectra using a ligand field multiplet approach allows us to obtain detailed information on the electronic structures of the metal ion in the two redox isomers. The temperature dependence of the spectra confirms the occurrence of a thermally induced VT transition and suggests that nucleation and distortion of the phase boundaries take place during the process. Moreover, optically induced metastable state formation is monitored at low temperatures--with a high degree of reproducibility--without changing the position of measurement on the sample during the experiment. This result paves the way for the use of such a highly sensitive technique for the investigation of photoswitchable materials in non-crystalline and nanostructured environments.