A biocompatible phosphorescent Ir(iii) oxygen sensor functionalized with oligo(ethylene glycol) groups: synthesis, photophysics and application in PLIM experiments

Abstract

NIR emitting Ir(iii) complexes decorated with oligo(ethylene glycol) were used to assess the degree of hypoxia in biosamples.

Biocompatible Ir(III) Complexes as Oxygen Sensors for Phosphorescence Lifetime Imaging

“…It is also worth noting that lifetime sensitivity of these complexes is relatively low that is typical for transition metal chromophores (e.g., iridium [ 27 ] and ruthenium [ 53 ] emitters) in aqueous media. Nevertheless, the lifetime interval of ca.…”

“…The instrumentation for the PLIM measurements is now commercially available and data processing algorithms are very well developed [ 17 , 18 ]. Qualitative assessments of the hypoxia regions in living organisms and cell compartments have been already performed by using a range of Pt, Pd, Ir, and Ru phosphorescent complexes, see reviews [ 16 , 19 , 20 , 21 , 22 ] and some recent experimental papers [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ], which demonstrated different lifetime sensitivity to oxygen and diverse levels of biocompatibility/toxicity. However, to exploit in full the PLIM mode of oxygen sensing, in particular, in order to obtain the quantitative spatial and temporal distribution of O 2 in biological systems, the targeted chemical design of the sensor composition and structure is highly necessary.…”

“…The last but not the least, emission lifetime changes through normal to hypoxic conditions fall in the range from hundreds of nanoseconds to a few microseconds that is more than order of magnitude shorter compared to the platinum and palladium porphyrins mentioned above. In our recent publication [ 27 ] we presented a series of iridium [Ir(N^C) 2 (N^N)] + complexes, which contain oligo(ethyleneglycol) (OEG) functions {–C(O)NHCH-(CH 2 OC 2 H 4 OC 2 H 4 OCH 3 ) 2 } at the periphery of the N^N and/or N^C ligands that made the hydrophobic core of these molecules water-soluble and suitable for semi-quantitative PLIM experiments on cell cultures. It has to be noted that the poly- and oligo-ethyleneglycole pendants have been already used to make molecular transition metal chromophores (Pt(II) [ 39 , 40 , 41 ], Pd(II) [ 42 , 43 ], Au(III) [ 44 ], Re(I) [ 45 , 46 ], Ir(III) [ 45 , 47 , 48 , 49 ], Ru(II) [ 50 ]) water-soluble, less toxic, and biocompatible.…”

Red‐to‐NIR Iridium(III) Emitters: Synthesis, Photophysical and Computational Study, the Effects of Cyclometallating and β‐Diketonate Ligands

“…[17] The complexes of this type possess a few characteristic features such as high chemical stability, bright luminescence and wide range of emission colors, which encompasses the whole visible spectrum from blue [18][19][20] to deep red [8,19] extending further to near-infrared (NIR) region. [8,[20][21][22] It is well established [23][24][25] that two major processes: metal-to-ligand charge transfer (MLCT) from Ir(III) ion to N^C ligands orbitals and N^C ligand centered (LC) transition dominate in formation of emissive triplet excited state of these chromophores. These observations indicate that fine tuning of emission wavelength, which is of key importance for various applications, can be done by variations in the nature and properties of the metalating N^C ligands.…”

Opportunities for Persistent Luminescent Nanoparticles in Luminescence Imaging of Biological Systems and Photodynamic Therapy

“…Longer emission lifetimes, in the range micro-millisecond, can be achieved using transition metal complexes or lanthanide(III) compounds. These compounds show unique spin forbidden and/or Laporte forbidden, in the case of the Ln III compounds, and are used in Phosphorescence Lifetime Imaging Microscopy (PLIM) [ 117 , 127 , 128 , 129 , 130 , 131 , 132 ]. Emission lifetimes higher than hundreds of nanoseconds allow complete elimination of the cell emission and yield a background-free image.…”