Proton-Coupled Electron Transfer in a Hydrogen-Bonded Charge-Transfer Complex.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Supramolecular Chemistry

Background:

• Proton-coupled electron transfer (PCET) is crucial in chemical and biological systems.
• Hydrogen-bonded charge-transfer (CT) complexes offer a platform for studying PCET mechanisms.
• Fluoride ion sensing is important in various analytical applications.

Purpose of the Study:

• To investigate the mechanism of PCET in a hydrogen-bonded CT complex involving 4-([2,2'-bipyridin]-4-yl)phenol (bpy-phenol) and a fluoride ion.
• To elucidate the role of hydrogen bonding and water in mediating ultrafast PCET reactions.
• To understand the dynamics of proton transfer in a water-restricted environment.

Main Methods:

• Ultrafast time-resolved transient absorption spectroscopy was employed.
• A charge-transfer complex between bpy-phenol and fluoride ion was synthesized.
• The influence of crystalline water in fluoride salt hydrates was examined.

Main Results:

• Photoexcitation induced ultrafast CT from phenol to bpy, initiating proton transfer.
• Two distinct proton transfer timescales (<150 fs and 3 ps) were observed.
• These timescales correlate with different hydrogen-bonding network configurations.
• Crystalline water within the fluoride salt hydrates was found to mediate the PCET reaction.

Conclusions:

• The study demonstrates ultrafast PCET in a fluoride-bound bpy-phenol complex.
• Hydrogen-bonded water bridges play a significant role in mediating PCET reactions, even in water-restricted environments.
• The findings provide insights into the fundamental mechanisms of PCET and ion sensing.