Luminescent Iridium-Terpyridine Complexes with Various Bis-Cyclometalated Ligands

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Photophysics
• Materials Science

Background:

• Bis-cyclometalated iridium complexes are crucial in developing advanced luminescent materials.
• The interplay between cyclometalating ligands and ancillary ligands dictates the photophysical behavior of iridium complexes.
• Understanding structure-property relationships is key to designing efficient light-emitting materials.

Purpose of the Study:

• To synthesize and structurally characterize a series of luminescent bis-cyclometalated iridium(III) complexes featuring 2,2':6',2″-terpyridine (tpy) and various cyclometalating (C^N) ligands.
• To investigate the impact of different C^N ligands (2-phenylpyridinate, benzo[h]quinolinate, 1-phenylisoquinolinate, 2-phenylbenzothiazolate) on the structural, photophysical, and electronic properties of the synthesized complexes.
• To elucidate the origin of luminescence through experimental data and theoretical calculations.

Main Methods:

• Synthesis of four novel [Ir(C^N)2(tpy)]PF6 complexes.
• Structural characterization using single-crystal X-ray diffraction.
• Photophysical measurements including emission spectra, luminescence lifetimes (τ), and absolute luminescence quantum yields (Φ).
• Density functional theory (DFT) calculations to determine the nature of the excited states.

Main Results:

• Structural analysis confirmed bidentate coordination of tpy ligands and revealed intramolecular π-π stacking and hydrogen bonding interactions.
• The C^N ligands significantly influenced photophysical properties, with complex 3 (1-phenylisoquinolinate) showing intense luminescence at 588 nm, a long lifetime (1965 nsec), and a moderate quantum yield (9.57%).
• DFT calculations indicated that luminescence originates from triplet metal-ligand to ligand charge transfer (3MLL'CT) excited states.

Conclusions:

• The study successfully synthesized and characterized novel iridium complexes, highlighting the critical role of C^N ligands in tuning luminescence.
• The observed structural features, such as π-π stacking and hydrogen bonding, contribute to the distinct photophysical properties.
• The findings provide valuable insights into the design principles for efficient phosphorescent iridium complexes for potential applications in optoelectronics.