OBSERVATION OF TRANSIENT HIGH-VALENT STATES IN THE WATER OXIDATION CATALYST CoIII4O4 CUBANE VIA EXTREME ULTRAVIOLET SPECTROSCOPY

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.35]{CubanePET.eps} \end{wrapfigure} The tetranuclear metal-oxo complex [Co$^{III}$$_{4}$O$_{4}$](OAc)$_{4}$(py)$_{4}$ is a homogeneous water oxidation catalyst and structural mimic of the oxygen evolving complex in photosynthetic organisms. The catalytic cycle involves a highly-oxidized intermediate the nature of which is controversial: leading formulations argue for either [Co$^{IV}$$_{2}$Co$^{III}$$_{2}$O$_{4}$] or [Co$^{V}$Co$^{III}$$_{3}$O$_{4}$]. We report the sensitization of the [Co$^{III}$$_{4}$O$_{4}$] cubane with a perylene bisimide dye thus enabling photoinduced electron transfer upon green light illumination and effecting a transient oxidation of the cobalt center(s). The resultant high-valent states and their dynamics are probed by ultrafast transient absorption and extreme ultraviolet (XUV) spectroscopies. XUV spectroscopy, by dint of its oxidation-state specificity, has the potential to reveal the true distribution of holes among cobalt centers within the oxidized cluster

THE USE OF POLYMER THIN FILMS AS TRANSMISSIVE SAMPLE SUPPORTS IN XUV SPECTROSCOPY

We discuss current challenges in the preparation of thin film samples for extreme ultraviolet (XUV) spectroscopy, and offer alternative methods which now enable this spectroscopy to be performed on a wide variety of previously inaccessible compounds. We explored the production, characterization, and use of polymer thin films as highly XUV transmissive sample supports, finding that such thin films could be made via a “slip-coating” technique in which polymer solution is deposited from the shearing meniscus between parallel sliding glass plates. Films made from polystyrene or polyvinyl chloride are thin (10$^{2}$-10$^{3}$ nm), homogeneously flat, smooth, and transmit more XUV light than do silicon nitride windows. The analytes of interest are directly cast upon the polymer surface, or codeposited from a common solution. In demonstration of the suitability of these methods towards XUV spectroscopy, we prepared samples of eight different first-row transition metal complexes and report their respective M-edge XANES spectra in the range of 40-90 eV. We additionally report the excited state difference spectrum of Fe(bpy)$_{3}$Cl$_{2}$ at 1.5 ps after visible excitation