A Dynamic Tetracationic Macrocycle Exhibiting Photoswitchable Molecular Encapsulation

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Designing responsive macrocycles for controlled host-guest interactions is complex.
• External stimuli are needed to control molecular container functions like solubilization and separation.
• Photo- and thermal-responsive elements offer precise control over molecular processes.

Purpose of the Study:

• To engineer a semi-rigid tetracationic cyclophane, OPVEx²Box⁴⁺, with photo- and thermal-responsive capabilities.
• To investigate the reversible switching between (EE)- and (EZ)-isomers upon light and heat stimuli.
• To demonstrate the control of host-guest binding affinities through external stimuli.

Main Methods:

• Synthesis of a novel tetracationic cyclophane incorporating oligo(p-phenylenevinylene) pyridinium units and extended viologens.
• Utilizing blue light irradiation and heating to induce reversible isomeric transformations.
• Characterizing guest binding affinities for different cyclophane configurations using charge-transfer and van der Waals interactions.

Main Results:

• The OPVEx²Box⁴⁺ cyclophane exhibits dramatically improved reversibility between (EE) and (EZ) isomers upon alternating blue light and heat.
• The (EE)-configuration effectively binds both electron-rich (e.g., anthracene) and electron-deficient (e.g., anthraquinone) guests.
• Blue light irradiation switches off guest binding by converting to the (EZ)-isomer, with binding restored upon heating.

Conclusions:

• Light and heat act as effective external stimuli to control host-guest interactions in the multi-responsive OPVEx²Box⁴⁺ macrocycle.
• The reversible switching mechanism provides a new platform for designing advanced molecular switches and machines.
• This work demonstrates a significant advancement in externally controllable molecular recognition and manipulation.