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Article

Novel NIR-Phosphorescent Ir(III) Complexes: Synthesis, Characterization and Their Exploration as Lifetime-Based O2 Sensors in Living Cells

Institute of Chemistry, Saint-Petersburg State University, Universitetskii pr., 26, 198504 St. Petersburg, Russia
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Academic Editor: Franck Meyer
Molecules 2022, 27(10), 3156; https://doi.org/10.3390/molecules27103156
Received: 20 April 2022 / Revised: 10 May 2022 / Accepted: 11 May 2022 / Published: 14 May 2022
A series of [Ir(N^C)2(N^N)]+ NIR-emitting orthometalated complexes (17) has been prepared and structurally characterized using elemental analysis, mass-spectrometry, and NMR spectroscopy. The complexes display intense phosphorescence with vibrationally structured emission bands exhibiting the maxima in the range 713–722 nm. The DFT and TD DFT calculations showed that the photophysical characteristics of these complexes are largely determined by the properties of the metalating N^C ligands, with their major contribution into formation of the lowest S1 and T1 excited states responsible for low energy absorption and emission, respectively. Emission lifetimes of 1–7 in degassed methanol solution vary from 1.76 to 5.39 µs and show strong quenching with molecular oxygen to provide an order of magnitude lifetime reduction in aerated solution. The photophysics of two complexes (1 and 7) were studied in model physiological media containing fetal bovine serum (FBS) and Dulbecco’s Modified Eagle Medium (DMEM) to give linear Stern-Volmer calibrations with substantially lower oxygen-quenching constants compared to those obtained in methanol solution. These observations were interpreted in terms of the sensors’ interaction with albumin, which is an abundant component of FBS and cell media. The studied complexes displayed acceptable cytotoxicity and preferential localization, either in mitochondria (1) or in lysosomes (7) of the CHO-K1 cell line. The results of the phosphorescence lifetime imaging (PLIM) experiments demonstrated considerable variations of the sensors’ lifetimes under normoxia and hypoxia conditions and indicated their applicability for semi-quantitative measurements of oxygen concentration in living cells. The complexes’ emission in the NIR domain and the excitation spectrum, extending down to ca. 600 nm, also showed that they are promising for use in in vivo studies. View Full-Text
Keywords: phosphorescence; iridium complexes; oxygen sensors; bioimaging phosphorescence; iridium complexes; oxygen sensors; bioimaging
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MDPI and ACS Style

Kritchenkov, I.S.; Mikhnevich, V.G.; Stashchak, V.S.; Solomatina, A.I.; Kozina, D.O.; Sokolov, V.V.; Tunik, S.P. Novel NIR-Phosphorescent Ir(III) Complexes: Synthesis, Characterization and Their Exploration as Lifetime-Based O2 Sensors in Living Cells. Molecules 2022, 27, 3156. https://doi.org/10.3390/molecules27103156

AMA Style

Kritchenkov IS, Mikhnevich VG, Stashchak VS, Solomatina AI, Kozina DO, Sokolov VV, Tunik SP. Novel NIR-Phosphorescent Ir(III) Complexes: Synthesis, Characterization and Their Exploration as Lifetime-Based O2 Sensors in Living Cells. Molecules. 2022; 27(10):3156. https://doi.org/10.3390/molecules27103156

Chicago/Turabian Style

Kritchenkov, Ilya S., Vitaliya G. Mikhnevich, Victoria S. Stashchak, Anastasia I. Solomatina, Daria O. Kozina, Victor V. Sokolov, and Sergey P. Tunik. 2022. "Novel NIR-Phosphorescent Ir(III) Complexes: Synthesis, Characterization and Their Exploration as Lifetime-Based O2 Sensors in Living Cells" Molecules 27, no. 10: 3156. https://doi.org/10.3390/molecules27103156

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