Room 304, Chemistry Building
Professor Paul Wagenknecht
Iron(II)-to-titanium(IV) metal-to-metal-charge transfer (MMCT) is important in the photosensitization of TiO2 by ferrocyanide, charge transfer in solid-state metal-oxide photocatalysts, and has been invoked to explain the blue color of sapphire, blue kyanite, and some lunar material, yet molecular examples of this phenomenon have not been investigated. We have prepared a series of complexes with alkynyl linkages between ferrocene (Fc) and TiIV and investigated the charge transfer by UV-Visible spectroscopy, electrochemistry, TRTAS, and TD-DFT. Complexes with two ferrocene substituents include Cp2Ti(C2Fc)2, Cp*2Ti(C2Fc)2, and Cp2Ti(C4Fc)2. Complexes with a single ferrocene utilize a titanocene with a trimethylsilyl derivatized Cp ring, TMSCp, and comprise the complexes TMSCp2Ti(C2Fc)(C2R), where R = C6H5, p-C6H4CF3, and CF3. All of the complexes with both Fc and Ti show an intense absorption between 540 and 630 nm that is absent in complexes lacking a ferrocene donor. The energy of the absorption tracks with the difference between the TiIV/III, and FeIII/II reduction potentials. Reorganization energies, l, have been determined using band shape analysis. Marcus-Hush type analysis of the electrochemical and spectroscopic data are consistent with the assignment of the low energy absorption as a MMCT band. TD-DFT analysis also supports this assignment. The electrochemical and spectroscopic data suggest that the TiIV/III reduction potential of the titanocene fragment is well-positioned to inject electrons into TiO2.
Paul grew up in Clearwater, FL and then obtained his B.S. in Chemistry from Furman University (1986) followed by a Ph. D. from Stanford (1991) with Professor Jim Collman. Following postdoctoral work at Colorado State University with Professor Jack Norton, he took a one-year adjunct position at Occidental College. After developing his own undergraduate research program at San Jose State University (1995 – 2003) he was called back to his alma mater, Furman University, in 2004. His interest in transition metal photophysics began during undergraduate research with Professor Noel Kane-Maguire and was further developed during sabbatical research with Professor Peter Ford at UCSB. His present research activities focus on the synthesis and photophysical characterization of transition metal complexes of interest for optoelectronics.