Research in the Wamser Group
at Portland State University
Artificial Photosynthesis
Solar Energy Conversion

General Research Areas:

organic chemistry, polymers, photochemistry, porphyrins

Useful background reading ( .pdf files ):

Donald Aitken (white paper for the International Solar Energy Society),
Transitioning to a Renewable Energy Future

U. S. Department of Energy Workshop,
Solar Energy Utilization

Greg Smestad & Michael Grätzel (Journal of Chemical Education),
Demonstrating Electron Transfer and Nanotechnology: A Natural Dye-Sensitized Nanocrystalline Energy Converter

Suman Cherian & Carl Wamser (Journal of Physical Chemistry),
Adsorption and Photoactivity of Tetra(4-carboxyphenyl)porphyrin (TCPP) on Nanoparticulate TiO2

Hooi-Sung (Brian) Kim & Carl Wamser (Photochemical & Photobiological Sciences),
Photoelectropolymerization of Aniline in a Dye-Sensitized Solar Cell

Specific project areas:

Back to the Wamser Home Page
Research in the Wamser lab is focused on solar energy conversion, using an approach called artificial photosynthesis. The long-term goal is development of a solar cell that efficiently collects solar energy and converts it to a useful form of chemical energy, such as the decomposition of water into hydrogen and oxygen using the energy of sunlight. Many of the design strategies are roughly based on natural membrane systems as used in photosynthesis. For example, the light-absorbing molecules used in the research are porphyrins, structural analogs of chlorophyll. Porphyrins are specifically organized in various ways to enhance their ability to collect solar energy, transfer their excitation energy to a reactive site, and initiate electron transfer reactions. Currently there are three main lines of research active in the Wamser group.

Thin films of polymeric porphyrins are created by the technique of interfacial polymerization. Two reactive porphyrin monomers are dissolved separately in immiscible liquids; rapid reaction occurs only at the interface between these two solutions, creating a thin polymer film. In the case of acid chloride and amine derivatives, a polyamide film is created. As the polymerization reaction proceeds, the interfacial film becomes a barrier that slows further reaction; hence interfacial polymer films can be exquisitely thin (10 - 100 nm). Nevertheless, these films absorb visible light well and undergo photoinduced charge transfer reactions that are directional, analogous to the charge transport membranes of natural photosynthesis. The directionality of these films is caused by an asymmetry of functional groups on the porphyrin units within the polymer film; specifically, excess amine groups appear on the surface of the film that was made in contact with the porphyrin amine derivative and excess carboxylic acid groups appear on the surface of the film that was made in contact with the porphyrin acid chloride derivative (acid chlorides are hydrolyzed to carboxylic acids during the workup of the finished film). This structural asymmetry of the thin films is a novel feature that is still under study both experimentally and theoretically. The structural asymmetry leads to the photochemical asymmetry because the redox potentials of the different porphyrins are such that electron transfer is favored from aminoporphyrins to carboxy-porphyrins.

The second approach under active investigation is sensitization of high surface area TiO2 semiconductor electrodes using porphyrin derivatives and porphyrin polymers. The use of high surface area semiconductors has recently led to remarkable improvements in the efficiency of solar cells and allowed the use of simple and inexpensive semiconductors such as TiO2. Since TiO2 is white (i.e., it absorbs in the ultraviolet but not in the visible), efficient collection of the solar spectrum requires sensitization by a molecule absorbing in the visible. We have demonstrated that our carboxyporphyrin derivative is an excellent sensitizer for TiO2, rapidly injecting an electron into TiO2 with high quantum efficiency. We are actively investigating various ways of attaching a series of porphyrins to TiO2 electrodes. This approach also uses the concept of directional electron transfer between porphyrins, with an electron transfer gradient from aminoporphyrin to carboxyporphyrin to TiO2.

We are also investigating the oxidative electropolymerizations of aminoporphyrins, which form conductive polymers apparently analogous to polyaniline. These polymers are being studied with respect to their structure, conductivity, acid-base, and redox properties. We have also started investigating copolymerizations with aniline. In particular, we would like to use these conductive polymers as components of a TiO2 solar cell. Aminoporphyrins and the related hydroxyporphyrins have an interesting set of spectroscopic properties, chracteristic of what are called hyperporphyrins, and we are also investigating the uv-visible and fluorescence spectroscopy of these compounds, in particular correlating their redox chemistry with their acid-base chemistry.

Individual research projects in the Wamser group can involve a great variety of possible areas, including synthesis, spectroscopy, computer modeling, electrochemistry, photochemistry, polymer chemistry, materials science, and combinations of any or all of the above. Additional new techniques and collaborations with colleagues at other institutions are always being sought to further characterize the novel properties of the polymers and thin films being developed.

Selected Research Publications:

Synthesis and Photoactivity of Chemically Asymmetric Polymeric Porphyrin Films Made by Interfacial Polymerization, C. C. Wamser, R. R. Bard, V. Senthilathipan, V. C. Anderson, J. A. Yates, H. K. Lonsdale, G. W. Rayfield, D. T. Friesen, D. A. Lorenz, G. C. Stangle, P. van Eikeren, D. R. Baer, R. A. Ransdell, J. H. Golbeck, W. C. Babcock, J. J. Sandberg, and S. E. Clarke, J. Amer. Chem. Soc. 1989, 111, 8485-8492.

Asymmetric Polyporphyrin Films by Interfacial Polymerization, C. C. Wamser, Mol. Cryst. Liq. Cryst. 1991, 194, 65-73.

Asymmetric Photopotentials from Thin Polymeric Porphyrin Films, C. C. Wamser, V. Senthilathipan, and W. Li, SPIE Proceedings 1991, 1436, 114-124.

Contact Angle Titrations Detect Surface Functional Group Asymmetry in Interfacially-Polymerized Films, C. C. Wamser and M. I. Gilbert, Langmuir 1992, 8, 1608-1614.

Substituent, Solvent, and Ionization Effects on the Redox Potentials of Free-Base Tetraphenylporphyrins, R. A. Ransdell and C. C. Wamser, J. Phys Chem. 1992, 96, 10572-10575.

Syntheses of a Series of Electron Donor and Electron Acceptor Derivatives, C. Hoefler, N. A. Kizilbash, and C. C. Wamser, Synth. Comm., 1993, 23 (9), 1339-1349.

Synthesis and Characterization of Interfacially Polymerized Films of Tetraphenylporphyrin Derivatives, W. Li and C. C. Wamser, Langmuir, 1995, 11, 4061-4071.

Thin Films of Polymeric Porphyrins: Interfacial and Electropolymerizations,
C. C. Wamser, J. Lebzelter, and C.-H. Ryu, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1996, 37(2), 384-385.

Directional Photoinduced Charge Transfer in Thin Polymeric Porphyrin Films, C. C. Wamser, The Spectrum, 1998, 11(3), 1-5.

Adsorption and Photoactivity of Tetra(4-carboxyphenyl)porphyrin (TCPP) on Nanoparticulate TiO2, S. Cherian and C. C. Wamser, J. Phys. Chem. B, 2000, 104(15), 3624-3629. ( .pdf file available )

Aqueous Complexation Equilibria of Tetra(4-carboxyphenyl)porphyrin with Viologens: Evidence for 1:1 and 1:2 Complexes and Induced Porphyrin Dimerization, S. E. Clarke, C. C. Wamser, and H. E. Bell, J. Phys. Chem. A, 2002, 106(13), 3235-3242.

Solar Cells with Porphyrin Sensitization, C. C. Wamser, H.-S. Kim, and J.-K. Lee, Opt. Mat., 2003, 21(1-3), 221-224. Corrigendum: 2004, 25, 445.

Substituent and Solvent Effects on the Hyperporphyrin Spectra of Diprotonated Tetraphenylporphyrins, J. Weinkauf, A. Schweiger, S. Cooper, and C. C. Wamser, J. Phys. Chem. A, 2003, 107(18), 3486-3496.

Photoelectropolymerization of Aniline in a Dye-Sensitized Solar Cell, H.-S. Kim and C. C. Wamser, Photochem. Photobiol. Sci., 2006, 5(10), 955-960. ( .pdf file available )

Synthesis of Amino/Carboxyporphyrins for Dye-Sensitized Solar Cells, M. G. Walter, Y. Zhao, R. Pi, J. Ruwitch. A. Denman, and C. C. Wamser, J. Org. Chem., 2006, submitted.