Radical-cation dimerization overwhelms inclusion in [N]pseudorotaxanes

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Chemical Engineering

Background:

• Cucurbit[7]uril (CB7) typically suppresses viologen radical cation dimerization in aqueous solutions.
• Viologen-based molecules are known for their redox activity and potential in molecular devices.
• Host-guest complexation is a key strategy for controlling molecular interactions.

Purpose of the Study:

• To investigate the behavior of multi-viologen thread molecules complexed with CB7 upon reduction.
• To demonstrate that viologen radical cation dimerization can act as a trigger for host-guest decomplexation.
• To explore the potential of this phenomenon in designing novel molecular switches.

Main Methods:

• Synthesis and characterization of viologen-containing thread molecules (BV(4+) and HV(12+)) and their CB7 complexes.
• Utilized techniques including (1)H DOSY NMR spectrometry, UV/Vis absorption spectrophotometry, square-wave voltammetry, and chronocoulometry.
• Investigated control systems using monomeric viologens (MV(2+) and BMV(2+)) and their CB7 complexes.

Main Results:

• Unlike control systems, reduction of BV(4+)⊂(CB7)2 and HV(12+)⊂(CB7)6 led to decomplexation and release of free threads.
• Reduced threads (BV(2(·+)) and HV(6(·+))) exhibited higher diffusion coefficients than their respective pseudorotaxanes.
• UV/Vis studies confirmed intramolecular radical-cation dimerization in the released threads.

Conclusions:

• Demonstrated counter-examples to the typical suppression of viologen radical cation dimerization by CB7.
• Established that radical cation dimerization can serve as a driving force for host-guest decomplexation.
• Validated the use of dimerization-induced decomplexation for creating novel molecular switches.