Mechanical Bond-Assisted Full-Spectrum Investigation of Radical Interactions.

Area of Science:

• Supramolecular Chemistry
• Chemical Physics
• Materials Science

Background:

• Molecular recognition via noncovalent bonding is crucial in chemical and biological systems.
• Investigating weak interactions in complex systems is challenging due to overlapping binding modes.
• The host-guest interactions between cyclobis(paraquat-p-phenylene) (CBPQT) and 4,4 '-bipyridinium (BIPY) radical cations are debated.

Purpose of the Study:

• To elucidate the binding modes between CBPQT and BIPY radical cations.
• To simplify the complex supramolecular system for clearer characterization.
• To explore new binding interactions in mechanically interlocked molecules.

Main Methods:

• Synthesis of a [2]catenane incorporating CBPQT and BIPY units.
• Comprehensive spectroscopic analysis (UV/vis/NIR, EPR, NMR).
• Electrochemical measurements and X-ray crystallography.

Main Results:

• Unambiguous identification of three binding modes between CBPQT and BIPY: bisradical tetracationic, trisradical tricationic, and bisradical dicationic.
• The [2]catenane model system facilitated the characterization of weak interactions.
• Discovery of two novel bisradical binding modes.

Conclusions:

• The mechanical bond-assisted approach is effective for studying noncovalent interactions.
• The newly discovered binding modes offer potential for self-assembled materials and supramolecular catalysis.
• This work clarifies the complex binding landscape of CBPQT and BIPY systems.