Molecular electronics

The miniaturization of electronic devices that use silicon-based technology will soon reach a limit and if devices are to continue getting smaller, scientists must harness the electronic properties of single molecules. A collection of Articles in this Focus highlights recent progress in the understanding and control of charge transport through single molecules.



Molecular electronics under the microscope p181


The field of molecular electronics has developed significantly as experimental techniques to study charge transport through single molecules have become more reliable. Three Articles in this issue highlight how chemists can now better understand and control electronic properties at the molecular level.

See also: Article by Dell et al. | Article by Su et al. | Article by Xiang et al.



Molecular length dictates the nature of charge carriers in single-molecule junctions of oxidized oligothiophenes pp209 - 214

Emma J. Dell, Brian Capozzi, Jianlong Xia, Latha Venkataraman & Luis M. Campos


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Understanding the intrinsic electronic properties of building blocks in conjugated materials can provide powerful design guidelines to control charge transport, such as tuning the nature of the charge carriers. Now, single-molecule transport studies of a family of oxidized oligothiophenes have shown that their molecular length determines the dominant carrier type.

See also: Editorial | Article by Su et al. | Article by Xiang et al.

Stereoelectronic switching in single-molecule junctions pp215 - 220

Timothy A. Su, Haixing Li, Michael L. Steigerwald, Latha Venkataraman & Colin Nuckolls


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Creating molecular components with controllable electronic properties is crucial to the realization of nanoscale devices. Now, a single-molecule conductance switch that operates through a stereoelectronic effect has been developed. The sub-ångström control of a scanning tunnelling microscope is used to switch reversibly between two distinct sets of rotational isomers, which differ greatly in their electronic character.

See also: Editorial Article by Dell et al. | Article by Xiang et al.

Intermediate tunnelling–hopping regime in DNA charge transport pp221 - 226

Limin Xiang, Julio L. Palma, Christopher Bruot, Vladimiro Mujica, Mark A. Ratner & Nongjian Tao


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Charge transport in molecular systems is typically through coherent tunnelling over a short distance or incoherent hopping over a long distance. An intermediate regime between those two transport mechanisms has now been found for DNA systems with stacked guanine–cytosine sequences.

See also: Editorial Article by Dell et al. | Article by Su et al.


From the archives

Sequence-independent and rapid long-range charge transfer through DNA pp156 - 159

Kiyohiko Kawai, Haruka Kodera, Yasuko Osakada & Tetsuro Majima


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The presence of adenine–thymine base pairs in DNA duplexes significantly reduces their electrical conductivity. However, by replacing adenine with a closely related analogue that does not disturb the normal complementary base pairing, it is possible to make duplexes that can transfer charge efficiently without having to use only guanine–cytosine base pairs.

Subject terms: Physical chemistry | Photochemistry

See also: News and Views by Genereux & Barton

Molecular electronics: DNA charges ahead pp106 - 107

Joseph C. Genereux & Jacqueline K. Barton


Some sequences of DNA conduct charge better than others. Replacing adenine with an analogue allows more sequences to transport charge effectively.

Subject terms: Physical chemistry | Photochemistry

Rectification and stability of a single molecular diode with controlled orientation pp635 - 641

Ismael Díez-Pérez, Joshua Hihath, Youngu Lee, Luping Yu, Lyudmyla Adamska, Mortko A. Kozhushner, Ivan I. Oleynik & Nongjian Tao


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The properties of molecular electronic devices can be tuned by tailoring the structures of the molecules from which they are built. Researchers now show that two closely related molecules — each containing a string of four aryl groups — behave very differently when strung between gold electrodes, with the non-symmetrical structure leading to diode-like behaviour.

Subject terms: Nanotechnology

See also: News and Views by Janes

Molecular electronics: Rectifying current behaviours pp601 - 603

David Janes


Inorganic semiconductors have long been used to construct rectifying diodes, but making them out of single molecules has remained a challenge. Now, two separate studies have induced rectification behaviour within molecular systems through different approaches.

Subject terms: Nanotechnology

Exploring local currents in molecular junctions pp223 - 228

Gemma C. Solomon, Carmen Herrmann, Thorsten Hansen, Vladimiro Mujica & Mark A. Ratner


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A methodology for describing local electronic transmission through bridging molecules between metallic electrodes is presented. Its application to simple alkane, phenyl and cross-conjugated systems highlights an unexpected number of cases whereby ‘through space’, rather than ‘through bond’ terms dominate and that interference effects coincide with the reversal of ring currents.

Subject terms: Theoretical chemistry | Physical chemistry

DNA charge transport over 34 nm pp228 - 233

Jason D. Slinker, Natalie B. Muren, Sara E. Renfrew & Jacqueline K. Barton


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The potential for using molecules as wires in nanoscale electronics is somewhat tempered by the challenges in making long and uniform structures. Now, it has been shown that DNA — which is easily synthesized to precise lengths — can conduct charge over 34 nm on multiplexed gold electrodes, a distance that surpasses most reports of molecular wires.

Subject terms: Biochemistry | Electrochemistry | Nanotechnology

The gold–sulfur interface at the nanoscale pp443 - 455

Hannu Häkkinen


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Thiolate-protected gold surfaces and interfaces are archetypal systems in various fields of current research in nanoscience, materials science, inorganic chemistry and surface science. Examples include self-assembled monolayers of organic molecules on gold, passivated gold nanoclusters and molecule–gold junctions. This Review discusses recent experimental and theoretical breakthroughs that highlight common features of gold-sulfur bonding in these systems.

Subject terms: Nanotechnology | Surface chemistry

Electron transfer through rigid organic molecular wires enhanced by electronic and electron–vibration coupling pp899 - 905

Junpei Sukegawa, Christina Schubert, Xiaozhang Zhu, Hayato Tsuji, Dirk M. Guldi & Eiichi Nakamura


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The relationship between electron-transfer properties and the structure of molecular electronics is still not fully understood. Now, a rigid and flat molecular wire has been shown to significantly enhance the rate of electron transfer compared with conventional flexible molecular wires. This enhancement is attributable to both conjugation-induced electronic coupling and inelastic electron tunnelling-enabled electron–vibration coupling.

See also: News and Views by Miller

Electron transfer: Lower tunnel barriers pp854 - 855

John R. Miller


A better understanding of electron transfer through molecules could provide the basis for many technological breakthroughs. Now, the rate of electron transfer has been enhanced in a family of molecules by making them more rigid, and this phenomenon may be explained by the loss of electronic energy to vibrations.

See also: Article by Sukegawa et al.

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