A water-soluble pH-triggered molecular switch.

Area of Science:

• Supramolecular Chemistry
• Molecular Machines
• Organic Chemistry

Background:

• Donor-acceptor [2]catenanes are mechanically interlocked molecules with potential applications in molecular devices.
• Bistability in catenanes allows for distinct structural states, crucial for molecular switching functionalities.
• The specific catenane investigated comprises a hydroquinone-containing crown ether and a 1,5-diaminonaphthalene unit, mechanically linked by a tetracationic cyclophane.

Purpose of the Study:

• To investigate the translational isomerism of a bistable donor-acceptor [2]catenane in solid-state and solution.
• To demonstrate the controlled switching of the catenane's isomeric states using chemical stimuli.
• To characterize the diprotonated derivative and confirm the selective inclusion of the hydroquinone unit within the cyclophane cavity.

Main Methods:

• UV/vis spectroscopy to monitor electronic changes associated with isomer switching.
• (1)H NMR spectroscopy to elucidate structural changes and confirm protonation states.
• Synthesis and characterization of the donor-acceptor [2]catenane and its derivatives.

Main Results:

• The [2]catenane exists as a mixture of translational isomers in both solid and solution states.
• Treatment with hydrochloric acid induces a switch, yielding a single diprotonated derivative.
• Spectroscopic evidence confirms that only the hydroquinone unit is encapsulated within the cyclophane cavity in the diprotonated state.
• The molecular switch can be reset using 1,4-diazabicyclo[2.2.2]octane.

Conclusions:

• The studied donor-acceptor [2]catenane functions as a bistable molecular switch with controllable states.
• Selective protonation and encapsulation demonstrate precise control over the relative positions of the interlocked components.
• This work highlights the potential of mechanically interlocked molecules for developing responsive and switchable systems.