Photoinduced One-Electron Chloride Oxidation in Water Using a Pentacationic Ir(III) Photosensitizer

Area of Science:

• Photochemistry
• Inorganic Chemistry
• Materials Science

Background:

• Chloride's high reduction potential (2.1-2.4 V vs NHE) limits its application in energy conversion.
• Artificial photosynthesis requires efficient methods for oxidizing abundant species like chloride.
• Iridium(III) complexes offer tunable redox properties for photocatalysis.

Purpose of the Study:

• To develop and investigate a novel iridium(III) photosensitizer for chloride photo-oxidation.
• To elucidate the kinetics and mechanism of the photoinduced electron transfer process.
• To assess the stability and potential applications of the photosensitizer in artificial photosynthesis.

Main Methods:

• Synthesis of a novel iridium(III) photosensitizer with pyridinium-decorated terpyridines.
• Stern-Volmer quenching experiments to study electron transfer kinetics.
• Nanosecond transient absorption spectroscopy to probe excited-state dynamics.
• Spectroelectrochemistry and photolysis to confirm product formation and assess stability.

Main Results:

• The iridium(III) photosensitizer efficiently mediates chloride photo-oxidation in water.
• Quenching rate constant (k_q) for photoinduced electron transfer was determined to be 5.0 × 10^10 M^-1 s^-1.
• Spectroelectrochemistry and photolysis confirmed the formation of the reduced photosensitizer.
• The photosensitizer demonstrated excellent redox and photostability.

Conclusions:

• The novel iridium(III) photosensitizer effectively overcomes the kinetic barriers for chloride oxidation.
• The demonstrated efficiency and stability position this photosensitizer as a promising candidate for hydrogen halide splitting.
• This work contributes to the advancement of photocatalytic systems for energy conversion and artificial photosynthesis.