| Research in the Wamser laboratory 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 two main lines of research active in the 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 carboxyporphyrins.
Individual research projects in the 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 p
roperties of the polymers and thin films being
developed.
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Thin Films of Polymeric Porphyrins: Interfacial and Electro-polymerizations, C. C. Wamser, J. Lebzelter, and C.-H. Ryu, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1996, 37(2), 384-385.
Synthesis and Characterization of Interfacially Polymerized Films of Tetraphenylporphyrin Derivatives, W. Li and C. C. Wamser, Langmuir, 1995, 11, 4061-4071.
Syntheses of a Series of Electron Donor and Electron Acceptor Derivatives, C. Hoefler, N. A. Kizilbash, and C. C. Wamser, Synth. Comm., 1993, 23, 1339-1349.
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.
Contact Angle Titrations Detect Surface Functional Group Asymmetry in Interfacially-Polymerized Films, C. C. Wamser and M. I. Gilbert, Langmuir 1992, 8, 1608-1614.
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.
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. Am. Chem. Soc. 1989, 111, 8485-8492.
Lejaren A. Hiller, Jr.: A Memorial Tribute to a Chemist-Composer, C. A. Wamser and C. C. Wamser, J. Chem. Educ., 1996, 73, 601-607.
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