Increasing Cage Escape Yields for Halide Oxidation in Aqueous Solutions Using Ir(III) Photosensitizers with...

Area of Science:

• Photochemistry
• Inorganic Chemistry
• Materials Science

Background:

• Iridium(III) complexes are vital photosensitizers in various chemical transformations.
• Understanding halide photo-oxidation mechanisms is key for developing efficient photocatalytic systems.
• Solvent effects significantly influence electron transfer dynamics and cage escape yields in photoinduced reactions.

Purpose of the Study:

• To synthesize and characterize five novel iridium(III) photosensitizers with π-extended aromatic ligands.
• To investigate the excited-state reactivity of these photosensitizers towards iodide, bromide, and chloride ions.
• To evaluate the influence of solvent composition (acetonitrile/water mixtures) on electron transfer and cage escape yields.

Main Methods:

• Synthesis and characterization of five Ir(III) photosensitizers.
• Photochemical studies in acetonitrile/water (50:50) mixtures.
• Nanosecond transient absorption spectroscopy to probe electron transfer dynamics.
• Determination of quenching rate constants and cage escape yields (ΦCE).

Main Results:

• All synthesized Ir(III) photosensitizers demonstrated reactivity towards iodide, bromide, and chloride.
• Quenching rate constants varied significantly across the halide series and were generally high.
• Nanosecond transient absorption spectroscopy confirmed electron transfer from halides to excited photosensitizers.
• Cage escape yields (ΦCE) were markedly higher in pure acetonitrile compared to acetonitrile/water mixtures.
• The introduction of π-extended aromatic ligands helped maintain appreciable cage escape yields (0.02–0.32) even in water-enriched conditions.

Conclusions:

• The developed Ir(III) photosensitizers exhibit efficient excited-state reactivity with halides.
• π-Extended aromatic ligands are crucial for enhancing cage escape yields in aqueous environments.
• These findings provide valuable insights for designing photosensitizers for photocatalytic applications in mixed aqueous solvents.