Ligand-Tuneable, Red-Emitting Iridium(III) Complexes for Efficient Triplet-Triplet Annihilation Upconversion...

Area of Science:

• Coordination Chemistry
• Photophysics
• Materials Science

Background:

• Cyclometallated iridium(III) complexes are crucial for luminescent applications.
• Tuning ligand structures offers a pathway to control photophysical properties.

Purpose of the Study:

• To synthesize and characterize novel iridium(III) complexes with substituted 2-phenylquinoxaline ligands.
• To investigate the impact of ligand substitution on visible emission properties and redox behavior.
• To evaluate the potential of these complexes as sensitizers in triplet-triplet annihilation upconversion (TTA-UC).

Main Methods:

• Synthesis of cationic, cyclometallated iridium(III) complexes.
• Spectroscopic characterization (absorption, time-resolved luminescence, transient absorption).
• Electrochemical measurements and theoretical calculations (Time-Dependent Density Functional Theory - TD-DFT).

Main Results:

• The complexes exhibited tunable absorption and phosphorescent emission in the visible region, attributed to metal-to-ligand charge-transfer (MLCT) transitions.
• Ligand substitution significantly influenced the electronic and photophysical properties.
• TD-DFT calculations accurately predicted emission wavelengths and supported assignments of spin-forbidden transitions.
• Methylated iridium(III) complexes demonstrated high efficiency in triplet-triplet annihilation upconversion, achieving quantum yields up to 39.3%.

Conclusions:

• Substituted 2-phenylquinoxaline ligands effectively tune the photophysical properties of iridium(III) complexes.
• The complexes are promising candidates for visible light applications, particularly as sensitizers in triplet-triplet annihilation upconversion.
• The study highlights the interplay between ligand design, electronic structure, and upconversion performance.