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SUPRAMOLECULAR EXTENSION CORD Light excitation induces electron transfer in socket-plug system MICHAEL FREEMANTLE A self-assembling supramolecular triad mimics, at a molecular level, the function of a macroscopic electrical extension cord, according to chemists in California and Italy. The triad consists of a wirelike central cationic component that plugs into crown ether sockets at both ends. One of the crown ethers is attached to an electron-rich bipyridyl ruthenium complex. When the system is illuminated, electrons flow from the ruthenium complex to the other end of the moiety. The work was carried out by chemistry professor Vincenzo Balzani and associate professor of chemistry Maria Teresa Gandolfi of the University of Bologna; chemistry professor J. Fraser Stoddart of the University of California, Los Angeles; and their coworkers [J. Am. Chem. Soc., published online Oct. 4, http://dx.doi.org/10.1021/ja025813x]. "This is an example of a supramolecular system specifically designed to play the role of a molecular-level device," Balzani tells C&EN. "Owing to the properties incorporated into the three components, self-assembly occurs in a specific, well-defined manner, and the two plug-socket connections can be controlled reversibly and independently by two different external inputs: acid/base and redox stimuli." The team monitored the behavior of the system by light absorption and emission spectroscopies and also by electrochemical techniques such as cyclic voltammetry. "This is a nice piece of work," comments Oxford University chemistry lecturer Harry L. Anderson. "The system illustrates the versatility of these molecular construction modules and shows how they can be used to build sophisticated and potentially functional supramolecular structures." The controlling phenomena brought into play are particularly interesting, according to John A. Gladysz, chemistry professor at the University of Erlangen-Nuremberg, in Germany. "The system embodies an added level of complexity and function beyond other supramolecular systems designed to function as molecular-level devices," he says. Balzani points to two limitations of the present system, however. "The middle component contains two plugs instead of a plug and a socket, giving a socket-plug-plug-socket architecture," he explains. "And the transferred electrons stop on the dicationic bipyridium unit without reaching the final naphthalene-containing crown ether component. We have designed, and recently synthesized, new molecular components that lead to two consecutive plug-socket motifs and place the final electron acceptor as the last component of the chain." |
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