| RESEARCH |
Another study shedding light on the property of a potential new nanoswitch design comes from the lab of University of South Carolina electrical engineering professor Jorge M. Seminario. Postdoc Pedro A. Derosa reported new insights into the switching properties of dinitropyridines, an achievement derived from work that the Army Research Office designated a "success story" in 2001. One particular molecule, 3-nitro-2-(3'-nitro-2'-ethynylpyridine)-5-thiopyridine, has two phenyl rings--each with a nitro group--separated by an acetylene group. Derosa modeled the molecule, which is connected at each end to gold contacts. He found that when the molecule is neutral, its two rings are 90° out of plane with each other. When the molecule is anionic, the two rings are in the same plane. The orbital-based explanation for the switching behavior derived from this picture is similar to Deng's. "Coplanarity implies a full delocalization of orbitals along the whole molecule," Derosa explained--which makes it easy for electrons to flow. But when the rings are in the out-of-plane configuration, he said, "the molecular orbitals are localized in a smaller spatial region without making a path connecting both ends, thus yielding a much larger resistance to the electron transfer." These computations are actually becoming a requirement in the design of molecular electronic devices, Derosa noted. "Not performing them would require trial-and-error experimentation." |
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