Paul S. Wagenknecht

Paul Wagenknecht

Professor, Chemistry

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Paul Wagenknecht grew up in Clearwater, Florida and obtained his bachelor of science in chemistry from Furman University in 1986. He was awarded a graduate fellowship from the National Science Foundation to attend Stanford University, and received his Ph.D. in Inorganic Chemistry in 1991.

Following postdoctoral studies at Colorado State University, he accepted a one-year adjunct teaching position at Occidental College in Los Angeles, California before beginning a tenure track position at San Jose State University in 1996. In 2004, he moved back to his alma mater, Furman University. Over his career, he has secured more than $2 million in external funding for support of undergraduate research in his group and department from agencies including the National Science Foundation, National Institutes of Health, William F. Keck Foundation, Arnold and Mabel Beckman Foundation, Research Corporation, Camille and Henry Dreyfus Foundation, and American Chemical Society.

Since beginning his independent career with undergraduate researchers, he has published more than 25 peer-reviewed research articles (mostly with student coauthors) and two patents. When not in the classroom or laboratory, he enjoys competing on the tennis courts and BBQ circuit (as AlQuemy BBQ).

Education

  • Ph.D., Stanford University
  • B.S., Furman University

Research

Adventures in Transition Metal Photophysics

State-of-the-art phosphorescent materials are integral to devices such as flat-screen displays and modern energy efficient lighting. Such materials efficiently convert electricity to light. The reverse process, the conversion of light into electricity, is perhaps even more technologically desirable. Our group studies complexes of metals such as iron, titanium, ruthenium, chromium, iridium, and rhodium as possible materials to improve these technologies.

MMCT in donor-π-bridge-acceptor complexes

Charge-transfer (CT) excited states where charge is separated over a long distance are interesting from a fundamental standpoint and for applications involving solar energy conversion and photocatalysis. Metal-to-metal CT (MMCT) excited states fall into this class and have been exploited for such applications. In particular, photocatalysis involving MMCT excited states in solid state Ti-O-M architectures involving TiIV acceptors oxo-bridged to donors (M) such as FeII, CrIII, and MnII has recently been investigated. Of additional relevance is that ferrocyanide photosensitizes TiO2, with the photosensitization being ascribed to an FeII to TiIV charge transfer. Furthermore, FeII to TiIVcharge transfer has been implicated as being responsible for the color observed in minerals such as blue sapphire (a corundum based gemstone) and blue kyanite (an aluminosilicate based gemstone). Our group is interested in molecular examples of FeII to TiIV charge transfer (Figure 1) and is involved in a systematic investigation of such complexes. These investigations involve collaborations with research groups outside of Furman who are experts in computational chemistry and ultrafast spectroscopy.
Figure 1. Adjusting the electron density at TiIV tunes the low energy absorption in a manner consistent with the assignment of this band as an FeII to TiIV MMCT. The MMCT is solvatochromic, shifting to lower energy with increased solvent polarizability. The reduction potential suggests the transient TiIII species is appropriate for electron injection into TiO2.

Photophysics of complexes with electron deficient alkyne ligands

Many transition metal complexes with alkynyl ligands are investigated for their luminescent properties. Of particular interest is adjusting the electronic properties of the metal/ligands, as this provides for the variation of colors observed in many complexes used in organic light emitting diodes (OLEDs). One common alkynyl ligand used to diminish the electron density at the metal is the pentafluorophenylethynyl ligand (C6F5C≡C). Our group is interested in even more electron deficient alkyne ligands and has turned to the trifluoropropynyl ligand (CF3C≡C). Electronically, this ligand behaves much like the cyano ligand. However, emission from a Rh(III) complex with this ligand, trans-[Rh(cyclam)(C2CF3)2]+, shows intense metal centered luminescence (Figure 2). We are presently investigating the relative electronic properties of C6F5C≡C and CF3C≡C through spectroscopic, voltammetric, and computational methods.


Figure 2. Emission of a RhIII complex with the trifluoropropynyl ligand. The emission is metal centered 3A2g to 1A1g (D4h) phosphorescence with a quantum yield of 0.11. Upon N-H deuteration, the quantum yield increases to 0.24 (24%).