Supramolecular Assembly of a Macrocyclic Rhodium(I) Isocyanide Complex with Long-Lived Near-Infrared Luminescence

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Photophysics

Background:

• Strategic ligand engineering is crucial for designing novel photoactive transition metal complexes.
• Controlling supramolecular stacking in square-planar d8-organometallic systems is an active area of research.

Purpose of the Study:

• To synthesize a macrocyclic tetradentate isocyanide ligand (CN4) for rhodium(I) coordination.
• To investigate the supramolecular aggregation and photophysical properties of the resulting rhodium complexes.

Main Methods:

• Synthesis of the macrocyclic ligand CN4 and its rhodium(I) complex [Rh(CN4)][BArF4].
• Single-crystal X-ray diffraction to determine the solid-state structure.
• UV-visible absorption spectroscopy and DOSY measurements to study aggregation in solution.
• Photophysical measurements including excited-state lifetime and emission spectroscopy.

Main Results:

• Formation of a tetrameric Rh(I) stack ([Rh(CN4)][BArF4]) was confirmed by X-ray diffraction.
• UV-vis spectroscopy revealed distinct absorption bands for dimeric (525 nm) and tetrameric (840 nm) species.
• Solvent-dependent aggregation was observed, with acetonitrile favoring tetramers and dichloromethane preventing aggregation.
• The tetrameric complex exhibited near-infrared absorption and emission (1040 nm) with a long excited-state lifetime (150 ns).

Conclusions:

• The novel CN4 ligand facilitates controlled one-dimensional stacking of rhodium(I) complexes.
• The resulting polynuclear architectures display unique photophysical properties, including near-infrared absorption and emission.
• This work opens avenues for developing advanced photoactive materials based on emergent properties of multinuclear metal complexes.