Photoresponsive Binding Dynamics in High-Affinity Cucurbit[8]uril-Dithienylethene Host-Guest Complexes

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Materials Science

Background:

• Controlling binding kinetics in supramolecular systems is crucial for developing molecular machines.
• Dithienylethene (DTE) photoswitches offer external stimuli control.
• Cucurbiturils are macrocyclic hosts with unique binding properties.

Purpose of the Study:

• To investigate the binding kinetics of a water-soluble cucurbit[8]uril host-guest system incorporating DTE photoswitches.
• To understand how structural modifications of DTE guests influence pseudorotaxane formation and dissociation.
• To demonstrate light-induced control over binding kinetics for advanced molecular devices.

Main Methods:

• Synthesis of cucurbit[8]uril and functionalized DTE guests.
• Kinetic studies of host-guest complex formation and dissociation.
• Spectroscopic analysis to monitor DTE isomerisation and binding events.

Main Results:

• A DTE guest with sulfonate side arms exhibited a >100,000-fold decrease in formation/dissociation rate compared to its bipyridinium analogue.
• A metastable product formed with the open DTE isomer, influencing overall binding kinetics.
• The closed DTE isomer showed ~100-fold slower dissociation (t½ = 107 h) than the open isomer (t½ = 1.2 h).

Conclusions:

• Structural modifications of DTE guests dramatically impact binding kinetics in cucurbit[8]uril systems.
• Light can be used to modulate the binding and dissociation rates, offering precise control.
• This work provides a foundation for light-responsive supramolecular machines and materials.