Dual emission from an iridium(III) complex/counter anion ion pair

Area of Science:

• Coordination Chemistry
• Photophysics
• Materials Science

Background:

• Iridium(III) complexes with 2,2':6',2''-terpyridine (tpy) ligands are known for their luminescent properties.
• The influence of counter anions on the photophysical behavior of such complexes is not fully understood.

Purpose of the Study:

• To investigate the dual-color luminescence of [Ir(tpy)2](PF6)3 in acetonitrile.
• To elucidate the nature of luminescence in [Ir(tpy)2]X3 (X = PF6-, Cl-, Br-, I-) complexes in solution and solid states.

Main Methods:

• Spectroscopic analysis (UV-Vis absorption and emission) of iridium complexes.
• Time-dependent density functional theory (TD-DFT) calculations.

Main Results:

• [Ir(tpy)2](PF6)3 in acetonitrile shows dual emission (blue and green) dependent on excitation wavelength, attributed to the [Ir(tpy)2]3+ cation and its ion pair [Ir(tpy)2]3+·PF6-.
• Emission in [Ir(tpy)2]I3 is assigned to a counter anion to complex ion charge-transfer transition, correlated with the electron affinity of the halide anion.
• TD-DFT calculations support the assignment of emissions to ligand-based transitions and charge-transfer transitions.

Conclusions:

• The counter anion plays a crucial role in determining the luminescence properties of [Ir(tpy)2]X3 complexes.
• Dual emission in acetonitrile arises from distinct emissive species: the free cation and its ion pair.
• The observed luminescence in crystalline [Ir(tpy)2]X3 is linked to counter anion interactions.