Photoswitchable rotaxanes on gold nanoparticles

Area of Science:

• Supramolecular Chemistry
• Nanotechnology
• Photochemistry

Background:

• Rotaxanes are mechanically interlocked molecules with potential applications in molecular machines.
• Gold nanoparticles (AuNPs) are versatile platforms for surface modification and sensing.
• Photoactive moieties enable external control over molecular motion.

Purpose of the Study:

• To functionalize gold nanoparticles with rotaxanes.
• To investigate the photo-induced switching behavior of rotaxanes on AuNP surfaces.
• To achieve unidirectional molecular motion on a solid support.

Main Methods:

• Synthesis of rotaxanes incorporating a photoactive acridane unit and a thioctic acid end-group.
• Deposition of rotaxanes onto gold nanoparticles via pseudorotaxane formation or thioctic ester exchange.
• Photo-induced switching of the acridane moiety to trigger ring movement along the molecular axle.
• Analysis of molecular motion on the gold nanoparticle surface.

Main Results:

• Successful deposition of rotaxanes onto gold nanoparticles using two distinct methods.
• Photoheterolysis of the acridane unit induced movement of the cyclobis(paraquat-p-phenylene) ring.
• The ring movement, initiated by charge changes, occurred between stations on the molecular axle.
• On the gold surface, the switching process resulted in unidirectional ring movement.

Conclusions:

• Rotaxanes can be effectively immobilized on gold nanoparticles.
• Photo-induced molecular switching is achievable on nanoparticle surfaces.
• The presence of the gold surface promotes unidirectional motion of the rotaxane ring, enabling controlled nanoscale movement.