Emission energy of azole-based ionic iridium(III) complexes: a theoretical study

Area of Science:

• Materials Science
• Inorganic Chemistry
• Computational Chemistry

Background:

• Cationic cyclometallated iridium(III) complexes are vital phosphorescent emitters.
• Azole ligands offer tunable electronic properties for iridium complexes.

Purpose of the Study:

• Investigate the influence of nitrogen atom number and position in azole ligands on iridium(III) complex electronic structure and emission wavelength.
• Determine how ligand incorporation site (cyclometalating C^N vs. ancillary N^N) affects emission shifts.

Main Methods:

• Theoretical density functional theory (DFT) calculations were employed.
• Studied cationic cyclometallated iridium(III) complexes with general formula [Ir(C^N)2(N^N)](+).
• Analyzed azole-based ligands with varying nitrogen atom content and positions.

Main Results:

• Increasing nitrogen atoms in azole ligands alters Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels.
• Emission wavelength shifts exceeding 100 nm were observed.
• Emission shifts to blue wavelengths when azoles are in C^N ligands; shifts to red when in N^N ligands.
• Nitrogen position within the azole ring significantly impacts emission energy, with specific arrangements causing marked blue shifts.

Conclusions:

• The number, position, and incorporation site of nitrogen atoms in azole ligands are critical for tuning the emission properties of iridium(III) complexes.
• DFT studies provide a predictive framework for designing novel iridium-based emitters with desired photophysical characteristics.