Three state redox-active molecular shuttle that switches in solution and on a surface

Area of Science:

• Supramolecular Chemistry
• Nanotechnology
• Surface Science

Background:

• Developing synthetic molecular machines for surface applications is crucial.
• Existing electrochemically switchable rotaxane shuttles primarily use viologen macrocycles.
• A need exists for alternative molecular shuttle systems compatible with surface integration.

Purpose of the Study:

• To report a novel [2]rotaxane molecular shuttle system.
• To demonstrate its ability to shuttle and switch positions in solution and on surfaces.
• To explore the electrochemical control over the shuttle's station binding affinity.

Main Methods:

• Synthesis of a [2]rotaxane featuring naphthalene diimide and succinamide hydrogen-bonding stations.
• Electrochemical characterization using cyclic voltammetry to study redox states and binding affinities.
• Immobilization onto gold surfaces via self-assembled monolayers and electrochemical analysis (EIS, chronoamperometry).

Main Results:

• The molecular shuttle demonstrated reversible switching between stations in solution and in a monolayer.
• The naphthalene diimide unit exhibited three accessible oxidation states, modulating binding affinity by six orders of magnitude.
• The shuttle's positive reduction potential allowed stable operation in self-assembled monolayers on gold.
• Redox-switched shuttling was confirmed on the millisecond timescale within the monolayer.

Conclusions:

• A new class of electrochemically switchable molecular shuttles based on naphthalene diimide and succinamide has been developed.
• This system offers robust electrochemical control and compatibility with surface-based applications.
• The findings pave the way for advanced molecular machines functioning on surfaces.