Unimolecular rectifier

A unimolecular rectifier is a single organic molecule which functions as a rectifier (one-way conductor) of electric current. The idea was first proposed in 1974 by Arieh (later Ari) Aviram, then at IBM, and Mark Ratner, then at New York University. Their publication was the first serious and concrete theoretical proposal in the new field of molecular electronics (UE). Based on the mesomeric effect of certain chemical compounds on organic molecules, a molecular rectifier was built by simulating the pn junction with the help of chemical compounds.

Their proposed rectifying molecule was designed so that electrical conduction within it would be favored from the electron-rich subunit or moiety (electron donor) to an electron-poor moiety (electron acceptor), but disfavored (by several electron volts) in the reverse direction.

Many potential rectifying molecules were studied by the groups of Robert Melville Metzger, Charles A. Panetta, and Daniell L. Mattern (University of Mississippi) between 1981 and 1991, but were not tested successfully for conductivity.

This proposal was verified in two papers in 1990 and 1993 by the groups of John Roy Sambles (University of Exeter, UK) and Geoffrey Joseph Ashwell (Cranfield University now at the Lancaster University, UK), using a monolayer of hexadecylquinolinium tricyanoquinodimethanide sandwiched between dissimilar metal electrodes (magnesium and platinum) and then confirmed in three papers in 1997 and 2001 by Metzger (now at the University of Alabama) and coworkers, who used identical metals (first aluminium, then gold).

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