Cyclometalated Anionic Benzimidazole-Based Luminescent Iridium Complexes with Tunable Organelle-Specific Cell Imaging

Area of Science:

• Organometallic Chemistry
• Bioinorganic Chemistry
• Materials Science

Background:

• Cyclometalated iridium complexes are widely explored for photophysical and biological applications.
• Benzimidazole-based ligands offer versatile coordination modes and tunable electronic properties.

Purpose of the Study:

• To synthesize and characterize novel neutral and cationic heteroleptic cyclometalated iridium complexes.
• To investigate their photophysical properties, cytotoxicity, and potential for organelle-specific bioimaging.

Main Methods:

• Synthesis and characterization using HRMS, multinuclear NMR, and single-crystal X-ray crystallography.
• Photophysical studies in various solvents, including quantum yield and lifetime measurements.
• Density functional theory (DFT) calculations for electronic structure analysis.
• Cytotoxicity assays (IC50) and cellular imaging in HeLa, B16F10, and CHO cells.

Main Results:

• Successful synthesis of neutral [1] and cationic [2] iridium complexes with anionic N^N benzimidazole ligands.
• Both complexes exhibit luminescence, with enhanced performance in water.
• DFT studies reveal HOMO localization on iridium and N^N ligand, LUMO on C^N ligand, indicating 3MLLCT emission.
• Complex [1] localizes in the endoplasmic reticulum, while complex [2] localizes in mitochondria in HeLa cells.
• Moderate cytotoxicity observed in cancer and normal cell lines.

Conclusions:

• The synthesized iridium complexes are luminescent and suitable for bioimaging applications.
• The complexes demonstrate organelle-specific localization, highlighting their potential as targeted phosphorescent probes.
• Further research could explore their therapeutic applications based on cytotoxicity profiles.