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David Bradley ISSUE #61
December 2006
Molecular Light Switch

According to Nobel laureate Roald Hoffmann, "Nanotechnology is the result of the marriage of the synthetic talent of Chemists with a device-driven ingenuity." With this thought in mind, Vincenzo Balzani of the University of Bologna introduces Reactive Reports to his latest chemical nano invention?a molecular scale solar power source, extension cable, and "drain" connection that functions as a signal processor that works in a chemical solution instead of on a printed circuit board.

Balzani's molecular-scale device is the result of a long research project and represents the next step forward in the processing of information with soft molecular-scale devices. In the long run, such devices will become the components of a chemical computer.

"We have developed the bottom-up construction, characterization, and operation of a molecular level system capable of performing signal processing in solution, dichloromethane in this case," he told Reactive Reports. "A peculiar and unprecedented aspect of the system is that it mimics, at the molecular level, the roles played in the macroscopic world by an electric source, an extension cable, and a drain."

As if that were not impressive enough, Balzani and his colleagues in Bologna, and Fraser Stoddart's team at the University of California at Los Angeles, have designed carefully the three components of their system so that it can reversibly assemble and disassemble itself under their control. The two connections are controlled independently by two distinct types of chemical input?an acid-base shift or a red-ox, reduction-oxidation, change. The units operate in series. "In the fully assembled system, excitation with visible light of the electron power unit (namely, a ruthenium complex, Ru(bpy)32+) is followed by the transfer of an electron, within nanoseconds to the bipyridinium electron drain through the extension cable."

"The ruthenium complex absorbs visible light and emits luminescence," explains Balzani. "When the three pieces are connected, the luminescence of this Ru complex is quenched because of competing electron transfer from the excited state to the viologen plug." He adds that the occurrence of electron transfer is documented by the appearance of the absorption spectrum of the reduced viologen.

Proc Natl Acad Sci USA, 2006, http://dx.doi.org/10.1073pnas.0606459103