Red-emitting heteroleptic iridium(III) complexes: photophysical and cell labeling study

Area of Science:

• Inorganic Chemistry
• Materials Science
• Biophysical Chemistry

Background:

• Heteroleptic iridium(III) complexes are investigated for their photophysical and biological applications.
• Developing efficient red-emitting probes with good water solubility and low cytotoxicity is crucial for bioimaging.

Purpose of the Study:

• To synthesize and characterize two novel red-emitting iridium(III) complexes, Ir-p and Ir-q.
• To evaluate their photophysical properties, including luminescence and quantum yield.
• To assess their potential as biological markers and their cytotoxicity in cellular environments.

Main Methods:

• Synthesis and structural confirmation of iridium(III) complexes using NMR, FT-IR, UV-Vis, and MALDI TOF.
• Photophysical characterization in ethanol and PBS solutions at room temperature and 77 K.
• Evaluation of water solubility, cytotoxicity (MTT assay), and cellular imaging via confocal and fluorescence microscopy.

Main Results:

• Both complexes exhibited red emission, with Ir-q showing a high quantum yield (11.5%) in PBS.
• Complexes demonstrated excellent water solubility and excitation wavelengths above 400 nm, distinct from biological autofluorescence.
• Low cytotoxicity was observed (IC50 > 116 μmol L⁻¹), with cellular uptake and cytoplasmic staining confirmed.

Conclusions:

• Ir-p and Ir-q are promising red-emitting iridium(III) complexes for bioimaging applications.
• Their favorable photophysical properties, water solubility, and low cytotoxicity support their use as biological markers.
• The complexes are effectively internalized by cells, localizing within the cytoplasm.