Tuning Conductance in π-σ-π Single-Molecule Wires

Area of Science:

• Molecular electronics
• Single-molecule electronics
• Quantum transport

Background:

• Conductance properties of pi-conjugated and sigma-conjugated systems are well-understood.
• Limited knowledge exists on the conductance of mixed sigma-pi backbone molecular wires.
• Understanding factors controlling transport properties in these wires is crucial for device applications.

Purpose of the Study:

• To investigate the conductance properties of molecular wires with pi-sigma-pi backbone structures.
• To determine how the sequence and composition of group 14 atoms (C, Si, Ge) influence electronic communication.
• To establish a molecular design concept for tuning conductance in single-molecule electrical devices.

Main Methods:

• Utilized a scanning tunneling microscope-based break-junction technique.
• Studied a series of molecular wires featuring thioanisole rings and triatomic alpha-beta-alpha chains (C, Si, Ge).
• Performed density functional theory calculations to elucidate conductance trends.

Main Results:

• The sequence and composition of group 14 atoms in the alpha-beta-alpha chain dictate electronic communication.
• Placing heavier atoms (Si, Ge) at the alpha-position decreases conductance, while at the beta-position increases it.
• The C-Ge-C sequence exhibited over 20 times higher conductivity than the Ge-C-Ge sequence.
• Observed periodic trends in conductance related to atomic size, polarizability, and electronegativity.

Conclusions:

• Periodic trends in group 14 elements govern molecular conductance in pi-sigma-pi systems.
• These trends are analogous to the alpha and beta silicon effects observed in physical organic chemistry.
• Findings provide a new molecular design strategy for controlling conductance in single-molecule electronic devices.