Selective lithium halide ion-pair sensing by a dynamic metalloporphyrin [2]rotaxane

Area of Science:

• Supramolecular Chemistry
• Chemical Sensing
• Coordination Chemistry

Background:

• Rotaxanes are mechanically interlocked molecules with potential applications in molecular machines and sensors.
• Metalloporphyrins offer unique photophysical and coordination properties for molecular recognition.
• Selective sensing of lithium halide ion pairs remains a challenge in analytical chemistry.

Purpose of the Study:

• To design and synthesize a dynamic zinc(II) metalloporphyrin-based [2]rotaxane for selective ion-pair recognition.
• To investigate the host-guest interactions and sensing mechanism of the rotaxane system.
• To demonstrate the optical sensing capabilities for lithium halide salts.

Main Methods:

• Synthesis of a heteroditopic macrocycle and a metalloporphyrin axle.
• ¹H NMR spectroscopy to study host-guest interactions and conformational changes.
• UV-visible absorption spectroscopy for optical sensing investigations.
• Titration experiments with cations, anions, and ion pairs.

Main Results:

• A strong interaction between the macrocycle and the zinc(II) metalloporphyrin axle was observed, inducing a conformational bias.
• Lithium halide ion-pair binding disrupted the mechanical bond interaction within the rotaxane.
• Dynamic macrocycle shuttling to a triazole station enabled cooperative recognition of LiX ion pairs.
• Selective optical sensing of lithium halide salts was achieved.

Conclusions:

• The developed [2]rotaxane acts as a sophisticated molecular sensor for lithium halide ion pairs.
• The sensing mechanism relies on the disruption of the mechanical bond and cooperative recognition.
• This work highlights the potential of dynamic rotaxanes in selective ion-pair sensing.