Host-Guest Interactions Enhance Charge Transport across Single Cyclodextrin/Azobenzene Complex Junction

Area of Science:

• Molecular electronics
• Supramolecular chemistry

Background:

• Azobenzene's charge transport properties are well-studied.
• The impact of host-guest complexation on azobenzene's molecular conductance is not well understood.

Purpose of the Study:

• To investigate how host-guest interactions between alpha-cyclodextrin (α-CD) and azobenzene affect single-molecule conductance in aqueous solution.
• To elucidate the role of molecular structure in modulating these effects.

Main Methods:

• Experimental techniques: Nuclear Magnetic Resonance (NMR) and Ultraviolet-Visible (UV-Vis) spectroscopy to confirm host-guest complex formation.
• Conductance measurements of amine-terminated azobenzene in aqueous solution with and without α-CD.
• Comparison with modified molecules: amine-terminated stilbene and thiomethyl-terminated azobenzene.
• Computational analysis: First-principles simulations to understand electronic structure changes.

Main Results:

• Formation of an α-CD/azobenzene host-guest complex driven by azobenzene's hydrophobicity.
• A ~3.5-fold increase in single-molecule conductance for amine-terminated azobenzene upon complexation.
• Progressive attenuation of conductance enhancement over time, attributed to α-CD aggregation.
• No significant conductance change observed for modified azobenzene or stilbene derivatives.

Conclusions:

• Host-guest interactions significantly modulate single-molecule conductance of azobenzene.
• The observed conductance enhancement is linked to the formation and stability of the α-CD/azobenzene complex.
• Structural modifications influence the sensitivity of molecular conductance to host-guest interactions.
• First-principles simulations support the experimental findings regarding electronic structure changes.