Gateway state-mediated, long-range tunnelling in molecular wires

Area of Science:

• Molecular electronics
• Quantum chemistry
• Materials science

Background:

• Electrical conductance (G) in single-molecule junctions typically decays exponentially with molecular length (L) as G = Ae^-βL.
• The attenuation coefficient (β) is traditionally attributed to electrode Fermi energy relative to molecular frontier orbitals, and the pre-exponential factor (A) to anchor groups.

Purpose of the Study:

• To investigate the influence of anchor group electronic states on the conductance decay coefficient (β).
• To explore a new design strategy for high-conductance molecular wires by optimizing electrode-molecule interface properties.

Main Methods:

• Experimental measurements of electrical conductance for various molecular structures.
• Theoretical calculations to model electron transport and electronic states.

Main Results:

• Demonstrated that electronic states on thiol anchor groups can significantly decrease β.
• Observed resonance effects near the Fermi energy (E_F) due to coupling between anchor group states and the molecular bridge.
• Showcased an interplay between gateway states and the central conjugated moiety influencing transmission probability.

Conclusions:

• The traditional model for conductance decay requires revision to include anchor group electronic effects.
• Exploiting electrode-molecule interface properties offers a novel pathway for designing high-transmission molecular wires.