Phosphorescent heavy-metal complexes for bioimaging

Abstract

The application of phosphorescent heavy-metal complexes with d(6), d(8) and d(10) electron configurations for bioimaging is a new and promising research field and has been attracting increasing interest. In this critical review, we systematically evaluate the advantages of phosphorescent heavy-metal complexes as bioimaging probes, including their photophysical properties, cytotoxicity and cellular uptake mechanisms. The progress of research into the use of phosphorescent heavy-metal complexes for staining different compartments of cells, monitoring intracellular functional species, providing targeted bioimaging, two-photon bioimaging, small-animal bioimaging, multimodal bioimaging and time-resolved bioimaging is summarized. In addition, several possible future directions in this field are also discussed (133 references).

Neutral N^C^N terdentate luminescent Pt(ii) complexes: their synthesis, photophysical properties, and bio-imaging applications

“…Such an effect can be most likely ascribed to the larger molecular size of the PtL 2 Cl when compared to PtL 1 Cl, since the longer polar (i.e., triethyleneglycol) chain is expected to impart a more amphiphilic character to the complex, thus helping to cross the lipophilic cellular membranes. 20,29,30 Moreover, it has been found that the derivative bearing the NCS ligand, namely PtL 1 NCS, shows the slowest cellular internalization kinetics. Indeed, for this complex the signal observed after one minute of incubation was almost negligible and photoluminescence started to appear after five minutes, yet with low intensity.…”

“…The investigation of platinum complexes for biological applications concerns mostly monomeric compounds, but aggregates show some important features as well: 19,20 (i) the emitter is shielded from the environment and in particular from dioxygen that could induce quenching; (ii) the rigidity, due to the packing of molecules in determined structures, decreases nonradiative processes; (iii) the reactivity or toxicity of the complexes is diminished by the difficult accessibility of the metal centre; (iv) changes in the excited state nature and properties lead to a bathochromic shift of excitation and emission towards more biologically interesting spectral windows and sometimes to an enhancement of the photophysical properties. In this respect, amongst all luminescent platinum derivatives, those bearing either an N^C^N 22,23 20,28,29 For this purpose, we decided to undertake a systematic study of the bio-imaging and cytotoxicity features of a series of platinum complexes bearing a N^C^N cyclometallated 1,3-di(2-pyridyl)-benzene by varying the molecular hydrophobic/hydrophilic ratio (through the introduction of ethyleneglycol moieties of different lengths) and the ancillary ligand, the incubating medium and the staining concentration. The choice of oligoethyleneglycol chains on the phosphorescent probe was based on their known ability to increase the aqueous solubility and bio-compatibility of luminescent iridium bio-labels.…”

Novel Cyclometalated Iridium(III) Xanthate Complexes and Their Phosphorescence Behavior in the Presence of Metal Ions

“…The former is assigned to typical spin-allowed 1 π-π* transitions of the ligands, and the latter to LLCT and 1 MLCT transition. The band at 450 nm may be assigned to the formally spin-forbidden 3 MLCT transition. Compared to Ir(dpppz)(ppz)(ipx), the corresponding absorption bands of complex Ir(ppz) 2 (ipx) have an obvious blue-shift after the partial hydrolysis of the cyclometalated ligand, which is consistent with …”

“…Recently, there is an increasing interest in the synthesis of cyclometalated Ir(III) complexes, which have found applications as phosphors in organic light emitting diodes (OLEDs) [1], sensors [2], and luminescent labels for biomolecules [3]. At the same time, sulfurcontaining ligands, such as dithiophosphates, dithiocarbamates and dithiocarbonates, have great binding potential to metals and have a wide range of uses in coordination chemistry [4].…”

Recent Advances on Functionalized Upconversion Nanoparticles for Detection of Small Molecules and Ions in Biosystems

“…Among all sensing technologies, photon‐signal‐based biosensors such as organic dyes,1, 2, 3, 4 metal complexes,5, 6, 7, 8, 9, 10 and semiconductor nanocrystals11 are the most commonly used ones. However, these probes have several limitations in detection or sensing.…”