Bis-cyclometalated iridium complexes with electronically modified aryl isocyanide ancillary ligands

Area of Science:

• Organometallic Chemistry
• Photophysics
• Electrochemistry

Background:

• Cationic biscyclometalated iridium(iii) complexes are crucial in photoluminescent applications.
• Tuning electronic and photophysical properties is key for optimizing device performance.
• Ancillary ligands play a significant role in modulating the behavior of metal complexes.

Purpose of the Study:

• To investigate the impact of ancillary ligand modifications on iridium(iii) complexes.
• To synthesize and characterize new iridium(iii) complexes with systematic ligand variations.
• To understand how electron-donating and electron-withdrawing groups affect electrochemical and photophysical properties.

Main Methods:

• Synthesis of nine new iridium(iii) complexes.
• Utilizing three distinct cyclometalating (C^N) ligands: 2,4-difluorophenylpyridine (F₂ppy), 2-benzothienylpyridine (btp), and 2-phenylbenzothiazole (bt).
• Employing three aryl isocyanide ancillary ligands: 2,4-dimethoxyphenyl isocyanide (CNAr^OMe), 3,5-bis(trifluoromethyl)phenyl isocyanide (CNAr^CF), and 4-nitrophenyl isocyanide (CNAr^NO).

Main Results:

• Ancillary ligand modifications showed minor shifts in absorption and emission bands.
• Aryl isocyanide ligands minimally perturb emissive states but control excited-state dynamics.
• Changes in substituents (electron-donating vs. electron-withdrawing) influenced radiative (k_r) and non-radiative (k_nr) decay rates, affecting lifetimes and quantum yields.
• Electronic structures were significantly altered, with perturbations up to 200 mV in the Ir^IV/Ir^III oxidation couple.

Conclusions:

• Systematic ancillary ligand modifications offer a route to tune excited-state dynamics and electronic structures of iridium(iii) complexes.
• The choice of cyclometalating ligand influences the magnitude of electronic perturbations.
• These findings provide insights for designing advanced iridium(iii) complexes for specific applications.