The unimolecular rectifier: unimolecular electronic devices are coming …

Abstract

Unimolecular electronic devices use the energy levels, or conformations, of one molecule or a very few molecules, and are contacted electrically from the outside. When made practical, these devices, the ‘advanced guard’ of unimolecular electronics, should leapfrog below the 50 nm limit of conventional inorganic microelectronics. Aviram and Ratner proposed in 1974 rectification of electrical current through a single molecule D-σ-A, 1, where D=good one-electron donor, σ=covalent, saturated ‘sigma’ bridge, A=good one-electron acceptor, because, from the undissociated ground state D 0 -σ-A 0 , the first zwitterionic excited state D + -σ-A – is accessible under electrical bias. Many such D-σ-A molecules were prepared. We found unimolecular rectification in a molecule, γ-hexadecylquinolinium tricyanoquinomethanide, 2, in which the ground state is zwitterionic: D + -π-A – , while the first excited state is undissociated: D 0 -π-A 0 .