Photosynthesis is the conversion of electromagnetic energy into stored chemical energy. The process, now well-understood at the molecular level, is schematically illustrated in Fig. 1 where the linear dimension of the membrane is ~5 nm. The primary event of photosynthesis, photon absorption leading to charge separation, occurs in a specialized structure: the photosynthetic reaction center. In higher plants there are two such reaction centers, Photosystems I and II, that have nanometer dimensions, picosecond response times and span a potential difference of one volt or more in their energized charge-separated state. The polarity of the voltage and vectorial nature of the charge separation is indicated in Fig. 1. The scientific focus and work plan of this proposal is on the interfacial physics and chemistry of isolated photosynthetic reaction centers and the construction of molecular logic devices using ORNL's unique experience in PS I self assembly, thin film and surface physics and instrumentation design and development. Fig. 2 is a schematic illustration of the extraction and isolation of Photosystem I reaction centers.
This poster presents an overview of the Oak Ridge National Laboratory research program in molecular electronics of photosynthetic reaction centers. We have had initial success in this area by demonstrating direct electrical contact of emergent electrons with the PS I reaction center by nanoparticle precipitation (Greenbaum, 1985; Greenbaum, 1988; J. W. Lee et al., 1998). Moreover, as illustrated in Fig. 3, our recent demonstration of stable diode properties of isolated reaction centers combined with the ability to orient them by self-assembly on a planar surface (I. Lee et al., 1995; I. Lee et al., 1997) make these structures good building blocks for 2-D and potentially 3-D device fabrication. Metallization of isolated PS I centers does not alter their fundamental photophysical properties (J. W. Lee et al., 1995) and they can be bonded to metal surfaces (J. W. Lee et al., 1996). Potential applications of PS I reaction centers for optoelectronic applications as well as molecular logic device construction will be discussed.
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