Photophysical Studies of Heteroleptic Iridium(III) Complexes with Phenylimidazole–Phenanthroline Derivatives for Oxygen Sensing

Iridium(III) complexes have attracted considerable attention owing to their outstanding photophysical properties, making them promising candidates for optoelectronic devices, bioimaging, and oxygen sensing. In this work, heteroleptic Ir(III) complexes containing 2-(2,4-difluorophenyl)pyridine (fppy) as cyclometalating ligands and PIB, PIB-CH₃, and PIB-4F as ancillary phenylimidazole–phenanthroline derivatives were synthesized and characterized by FTIR, ¹H, ¹³C, and ¹⁹F NMR, COSY, NOESY, HSQC, and high-resolution ESI-TOF mass spectrometry. Photophysical studies were performed in 1.0 × 10⁻⁵ mol L⁻¹ solutions using UV–Vis absorption, excitation, emission, photoluminescence quantum yield, and excited-state lifetime measurements under aerated and nitrogen-saturated conditions. The complexes exhibited intense ligand-centered absorption bands between 270–280 nm and broad emission centered at approximately 510 nm, characteristic of mixed ³LC/³MLCT excited states. Nitrogen saturation increased the photoluminescence quantum yield from approximately 1% to 5%, confirming oxygen-responsive phosphorescence and highlighting the potential of these complexes for future oxygen-sensing applications.