Chiroptical inversion of a planar chiral redox-switchable rotaxane

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Chiroptical Materials

Background:

• Development of redox-active rotaxanes for advanced molecular machines.
• Introduction of planar chirality into mechanically interlocked molecules.
• Exploration of chiroptical switching mechanisms in molecular systems.

Purpose of the Study:

• To design and synthesize a novel redox-active [2]rotaxane incorporating planar chirality.
• To investigate the chiroptical properties and electrochemical behavior of the synthesized rotaxane.
• To elucidate the mechanism behind the observed electrochemically induced chiroptical switching.

Main Methods:

• Synthesis of a tetrathiafulvalene (TTF)-containing crown ether macrocycle and a non-symmetric axle.
• Formation and characterization of the mechanically planar chiral [2]rotaxane.
• Enantiomeric separation using chiral High-Performance Liquid Chromatography (HPLC).
• Electrochemical analysis (cyclic voltammetry) and Electronic Circular Dichroism (ECD) spectroscopy.
• Computational studies including Density Functional Theory (DFT) calculations.

Main Results:

• Successful design and synthesis of a mechanically planar chiral [2]rotaxane.
• Achieved enantiomeric separation of the rotaxane, confirming its chirality.
• Demonstrated reversible oxidation of the TTF unit, with electrochemical properties similar to non-chiral controls.
• Observed reversible inversion of the main ECD band upon oxidation of the individual enantiomers.
• Experimental and computational data indicate electronic effects of oxidation drive chiroptical switching.

Conclusions:

• The synthesized rotaxane is the first example of an electrochemically switchable system exhibiting reversible inversion of its main ECD band.
• The study highlights the potential of redox-active components and mechanical chirality for developing responsive molecular materials.
• Oxidation-induced electronic changes are the primary drivers for the observed chiroptical switching behavior.