Electron-Transfer Rates in Host-Guest Assemblies at β-Cyclodextrin Monolayers

Area of Science:

• Supramolecular Chemistry
• Electrochemistry
• Surface Science

Background:

• Beta-cyclodextrin (βCD) host molecules can be immobilized on conductive surfaces.
• The distance between the βCD host and the substrate can influence electron transfer kinetics.

Purpose of the Study:

• To investigate how the distance between a βCD host core and a conductive substrate affects electron transfer rates.
• To evaluate short-tethered βCD adsorbates for studying short-distance electron transfer.

Main Methods:

• Fabrication of βCD monolayers with varying anchoring groups on conductive substrates.
• Immobilization of electrochemically active guests onto βCD host monolayers.
• Electrochemical measurements including impedance spectroscopy, cyclic voltammetry, and capacitance spectroscopy.
• Study of electron transfer using free-diffusing probes like Fe(CN)63-/4-.

Main Results:

• Electron transfer of diffusing probes was significantly faster (3 orders of magnitude) when βCD cores were close to the surface compared to when separated by undecyl chains.
• Electron transfer rates for immobilized guests varied up to a factor of 8 across different βCD monolayers.
• Iodine- and nitrile-functionalized βCD monolayers achieved near-maximum packing density.

Conclusions:

• Increasing the distance between the βCD host core and the conductive substrate diminishes the electron-transfer rate.
• Surface functionalization and molecular architecture are critical for controlling electron transfer in βCD-modified systems.