Tris-cyclometalated iridium complexes in imaging and catalysis

Abstract

A series of luminescent tris-cyclometalated iridium(III) complexes has been synthesized and characterized by 1H-NMR, 13C-NMR and MS spectroscopies. The photophysical properties of the complexes were investigated by using UV-Vis, steady state photoluminescence, and time-resolved photoluminescence techniques. Specifically, a group of derivatives of the prototypical complex fac-[Ir(ppy)3] bearing various aminoalkyl sidechains, alkyl chain is terminated with a hydroxy group, and quarternary ammonium salts have been investigated with major focus on understanding the relationship between the structure, aggregation behavior, as a potential cellular imaging probe and photoredox catalysis. The complexes possess interesting properties including long luminescent lifetime in aqueous media. The length of the aminoalkyl sidechains and their nature (hydrophilic vs hydrophobic) affects the ability of the complexes to aggregate in the solutions with high content of water. The iridium(III) complexes with one and two 2-hydroxy ethyl groups on the nitrogen atom exhibit similar quantum yield to the parent complex fac-[Ir(ppy)3] and the second of these also exhibits low cytotoxicity. The quarternary ammonium salts exhibits rapid photoreactivity, which can be used for the formation of new products. The complexes have been investigated as a potential cellular stain in NIH-3T3 cells. Tris-cyclometalated iridium(III) complex containing a single quarternary ammonium salt is less cytotoxic than aminoalkyl predecessor and shows lysosomal localization as its precursor. Finally, photoredox catalysis experiments carried out with the synthesized iridium(III) complexes show their ability to act as photoredox catalysts. Furthermore, iridium(III) complex immobilized on aminomethyl polystyrene shows promise as heterogeneous catalyst, as it appears to be stable and active after recycling in organic synthesis reaction.

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