Protonation-Independent Charge Transport Across Diphenylamine Single-Molecule Junctions

Area of Science:

• Molecular Electronics
• Organic Chemistry
• Physical Chemistry

Background:

• Amines are common in molecular junctions, but their role in charge transport via protonation is unclear.
• Understanding amine protonation effects is crucial for designing molecular electronic devices.

Purpose of the Study:

• To investigate how the protonation state of a central amine group affects charge transport in a diphenylamine molecular backbone.
• To elucidate the mechanism behind conductance changes upon amine protonation.

Main Methods:

• Synthesized and studied a diphenylamine molecular backbone.
• Utilized ultraviolet-visible spectroscopy to confirm amine protonation.
• Performed electrochemical measurements of charge transport across the molecular junction under varying bias voltages.

Main Results:

• Confirmed protonation of diphenylamine using trifluoroacetic acid or HCl.
• Observed a modest increase in conductance for protonated diphenylamine.
• Identified the highest occupied molecular orbital (HOMO) as the primary charge transport channel.
• Found that protonation shifts the HOMO resonance energy closer to the Fermi level.

Conclusions:

• Protonation of the amine group in diphenylamine enhances electron conduction.
• The observed conductance increase is attributed to the HOMO resonance energy aligning more favorably with the Fermi level.
• This work provides insights into controlling charge transport in molecular junctions through amine functionalization.