Redox-Responsive H-Bonding: Amplifying the Effect of Electron Transfer Using Proton-Coupled Electron Transfer.

Area of Science:

• Supramolecular Chemistry
• Electrochemistry
• Organic Chemistry

Background:

• Hydrogen-bond (H-bond) dimers are crucial in molecular recognition.
• Secondary H-bonds significantly influence the overall binding strength of H-bond dimers.
• Controlling H-bond dimer stability through external stimuli is a key challenge.

Purpose of the Study:

• To propose and demonstrate a new strategy for creating highly redox-responsive H-bond dimers.
• To leverage proton-coupled electron transfer (PCET) to modulate H-bond dimer stability.
• To investigate the role of secondary H-bonds in PCET-driven binding enhancement.

Main Methods:

• Design and synthesis of an electroactive donor-acceptor-donor (DAD) array (H(MQ+)H) and an electroinactive acceptor-donor-acceptor (ADA) array (O(NH)O).
• Nuclear Magnetic Resonance (NMR) titration to determine initial binding constants (Kassoc).
• Cyclic voltammetry (CV) to study redox behavior and binding changes upon reduction.

Main Results:

• The H(MQ+)H:O(NH)O dimer exhibited a typical Kassoc of 500 M⁻¹ in its oxidized state.
• Two-electron reduction of the system resulted in a 1.8 × 10⁵-fold increase in binding strength.
• The reduced state showed a Kassoc of 9 × 10⁷ M⁻¹, characteristic of strong DDD-AAA H-bond dimers, indicating proton transfer.

Conclusions:

• The proposed PCET strategy effectively creates highly redox-responsive H-bond dimers.
• Electron transfer triggers proton transfer, significantly strengthening H-bond interactions.
• This approach offers a powerful method for designing switchable molecular recognition systems.