Electrical molecular switch addressed by chemical stimuli

Area of Science:

• Molecular electronics
• Organic chemistry
• Quantum transport

Background:

• Benzo-bis(imidazole) derivatives are promising for molecular electronics.
• Protonation significantly alters molecular electronic properties.
• Functional group choice is critical for tuning molecular conductance.

Purpose of the Study:

• To investigate the effect of protonation on the conductance of benzo-bis(imidazole) molecules.
• To determine how lateral functional groups influence conductance switching behavior.
• To elucidate the underlying electronic mechanisms governing conductance changes.

Main Methods:

• Fabrication and characterization of molecular junctions (self-assembled monolayers, nanodot-molecule junctions, single molecules).
• Conductance measurements under varying conditions.
• Ab initio theoretical calculations (e.g., density functional theory) to model electronic structure.

Main Results:

• Protonation of H-substituted benzo-bis(imidazole) increases conductance (Gpro > Gneu).
• Protonation of amino-phenyl functionalized benzo-bis(imidazole) decreases conductance (Gneu > Gpro).
• Observed effects are consistent across different junction scales.

Conclusions:

• Lateral functional groups dictate the direction of conductance change upon protonation in benzo-bis(imidazole) systems.
• For H-substituted molecules, reduced LUMO-HOMO gap explains increased conductance.
• For amino-phenyl functionalized molecules, a HOMO shift reducing density of states at Fermi energy explains decreased conductance.