Visible Light Driven Nanosecond Bromide Oxidation by a Ru Complex with Subsequent Br-Br Bond Formation

Area of Science:

• Photochemistry and Photophysics
• Inorganic Chemistry
• Solar Energy Conversion

Background:

• Ruthenium complexes are widely studied for their photophysical properties.
• Bromide oxidation is a key step in various chemical processes, including energy storage.
• Understanding excited-state reactivity is crucial for developing photocatalytic systems.

Purpose of the Study:

• To investigate the visible light-induced reactivity of [Ru(deeb)(bpz)2](2+) with bromide ions (Br(-)).
• To elucidate the mechanisms of excited-state quenching and electron transfer.
• To assess the potential of this system for solar energy conversion.

Main Methods:

• Excitation of the ruthenium complex with visible light in acetone solutions containing bromide.
• Spectroscopic techniques including 1H NMR, UV-vis absorption, and photoluminescence measurements.
• Kinetic analysis to determine rate constants for electron transfer and product formation.
• Application of Marcus theory to estimate redox potentials.

Main Results:

• Visible light excitation led to the formation of dibromide (Br2(•-)), storing approximately 1.65 eV of free energy.
• Two quenching mechanisms were identified: diffusional quenching and an inner-sphere pathway involving ligand association.
• Rate constants for electron transfer and dibromide formation were determined.
• The estimated reduction potential of Br(•)/Br(-) in acetone was found to be 1.22 V vs SCE.

Conclusions:

• The studied ruthenium complex efficiently oxidizes bromide ions upon visible light excitation.
• The observed rapid bromide oxidation by molecular excited states holds promise for solar energy applications.
• The findings contribute to understanding light-driven redox processes and energy storage mechanisms.