Radical-to-radical push-pull effect enhances single-molecule conductance in asymmetric diradicals

Area of Science:

• Molecular electronics
• Quantum chemistry
• Materials science

Background:

• Asymmetry in diradicals creates unique push-pull electron spin effects.
• Diradical substructures can be integrated into molecular wires for electronic studies.

Purpose of the Study:

• To investigate the conductance of asymmetric diradicals using single-molecule junction techniques.
• To establish relationships between intramolecular radical-radical coupling and single-molecule conductance.

Main Methods:

• Utilized scanning tunneling microscope break junction technique to measure conductance.
• Synthesized asymmetric diradicals appended to a bisphenyl-thiophene segment linked to electrodes.
• Analyzed conductance in both non-radical and diradical states.

Main Results:

• Observed increased conductance in diradicals compared to their non-radical counterparts.
• Attributed conductance enhancement to new intragap states and an additional conjugation channel via hypervalent sulfur.
• Found conductance reduction with increased donor-acceptor moiety size due to competing electronic forms.

Conclusions:

• Single-molecule junction techniques enable the study of diradical conductance tuning.
• Push-pull electron spin effects in asymmetric diradicals significantly modulate molecular conductance.
• Molecular orbital and valence bond theories explain the observed conductance changes.