Herein we report four [Ir(NC)(2)(LL)](n+), n = 0,1 complexes (1-4) containing cyclometallated NC ligand (NCH = 1-phenyl-2-(4-(pyridin-2-yl)phenyl)-1H-phenanthro[9,10-d]imidazole) and various bidentate LL ligands (picolinic acid (1), 2,2 '-bipyridine (2), [2,2 '-bipyridine]-4,4 '-dicarboxylic acid (3), and sodium 4,4 ',4 '',4"'-(1,2-phenylenebis(phosphanetriyl))tetrabenzenesulfonate (4). The NCH ligand precursor and iridium complexes 1-4 were synthesized in good yield and characterized using chemical analysis, ESI mass spectrometry, and NMR spectroscopy. The solid-state structure of 2 was also determined by XRD analysis. The complexes display moderate to strong phosphorescence in the 550-670 nm range with the quantum yields up to 30% and lifetimes of the excited state up to 60 mu s in deoxygenated solution. Emission properties of 1-4 and NCH are strongly pH-dependent to give considerable variations in excitation and emission profiles accompanied by changes in emission efficiency and dynamics of the excited state. Density functional theory (DFT) and time-dependent density functional theory (TD DFT) calculations made it possible to assign the nature of emissive excited states in both deprotonated and protonated forms of these molecules. The complexes 3 and 4 internalize into living CHO-K1 cells, localize in cytoplasmic vesicles, primarily in lysosomes and acidified endosomes, and demonstrate relatively low toxicity, showing more than 80% cells viability up to the concentration of 10 mu M after 24 h incubation. Phosphorescence lifetime imaging microscopy (PLIM) experiments in these cells display lifetime distribution, the conversion of which into pH values using calibration curves gives the magnitudes of this parameter compatible with the physiologically relevant interval of the cell compartments pH.

Original languageEnglish
Article number232
Number of pages20
JournalMolecules
Volume27
Issue number1
Early online dateDec 2021
DOIs
StatePublished - 1 Jan 2022

    Scopus subject areas

  • Drug Discovery
  • Analytical Chemistry
  • Chemistry (miscellaneous)
  • Molecular Medicine
  • Physical and Theoretical Chemistry
  • Pharmaceutical Science
  • Organic Chemistry

    Research areas

  • Orthometalated iridium(III) complexes, PH-dependent luminescence, Phosphorescence lifetime imaging, Cell Line, Chemistry Techniques, Synthetic, Magnetic Resonance Spectroscopy, Molecular Conformation, Iridium/chemistry, Models, Molecular, Molecular Imaging, Animals, X-Ray Diffraction, Chemical Phenomena, Ligands, Molecular Structure, Hydrogen-Ion Concentration, Organometallic Compounds/chemical synthesis, DESIGN, IR(III), CHEMISTRY, phosphorescence lifetime imaging, PROBE, ACIDITY, PHOTOCHEMICAL PROPERTIES, orthometalated iridium(III) complexes, pH-dependent luminescence

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