Coordination-Driven Self-Assembly of Cyclometalated Iridium Squares Using Linear Aromatic Diisocyanides

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Cyclometalated iridium(III) complexes are valuable for their photophysical properties.
• Self-assembly offers a route to complex supramolecular structures.
• Developing efficient methods for constructing iridium-based coordination cages is an ongoing challenge.

Purpose of the Study:

• To demonstrate facile [4 + 4] coordination-driven self-assembly of cyclometalated iridium(III) complexes.
• To synthesize and characterize a new family of iridium(III) coordination cages using linear aryldiisocyanide bridging ligands.
• To investigate the photophysical properties of the resulting supramolecular coordination compounds.

Main Methods:

• One-pot synthesis of [Ir(C^N)₂(μ-BL)]₄⁴⁺ coordination cages.
• Characterization using ¹H NMR spectroscopy and high-resolution mass spectrometry.
• Detailed photophysical studies, including phosphorescence measurements.

Main Results:

• Successfully synthesized nine new M₄L₄ square coordination cages with varying cyclometalating ligands (ppy, bt, piq) and bridging ligands (BLs).
• Achieved isolated yields of 40-83% for the supramolecular coordination compounds.
• Observed phosphorescence primarily from the iridium(III) nodes, with emission color tunable by the cyclometalating ligand; in some cases, emission originated from the bridging ligand.

Conclusions:

• Aromatic diisocyanide ligands facilitate the coordination-driven assembly of inert iridium(III) nodes under mild conditions.
• The developed method yields supramolecular coordination complexes with controllable and desirable photophysical characteristics.
• This work expands the toolkit for constructing sophisticated iridium-based supramolecular architectures for potential applications in luminescence and materials science.