Halide-Enhanced Spin-Orbit Coupling and the Phosphorescence Rate in Ir(III) Complexes.

Area of Science:

• Photochemistry and Photophysics
• Organometallic Chemistry
• Materials Science

Background:

• Phosphorescence in Iridium(III) complexes is typically spin-forbidden.
• Spin-orbit coupling (SOC) mediated by the metal center relaxes this restriction.
• Enhancing SOC via auxiliary ligands can further increase phosphorescence rates.

Purpose of the Study:

• To synthesize and characterize a dinuclear Iridium(III) complex with iodide ligands.
• To investigate the effect of metal-coordinated halides on SOC and phosphorescence properties.
• To correlate structural modifications with photophysical performance.

Main Methods:

• Synthesis of a dinuclear Iridium(III) complex containing Ir(III)-iodide moieties.
• Photoluminescence spectroscopy at room and cryogenic temperatures.
• Decay time measurements and zero-field splitting (ZFS) determination.
• Theoretical calculations to elucidate SOC contributions.

Main Results:

• The dinuclear Ir(III)-iodide complex exhibits intense phosphorescence (ΦPL = 90%) with a short decay time (τ = 0.34 μs) at 300 K.
• Cryogenic studies revealed short individual decay times for T1 substates, indicating strong SOC.
• Theoretical analysis confirmed halide contribution to SOC, acting in tandem with the metal center.
• Comparative study with an analogous Ir(III)-chloride complex showed enhanced SOC and phosphorescence rates with iodides.

Conclusions:

• Metal-coordinated halides, especially iodides, significantly enhance spin-orbit coupling in Iridium(III) complexes.
• This enhancement leads to accelerated phosphorescence rates, making these complexes promising for applications.
• The study highlights the tunability of photophysical properties through ligand design.