Near-infrared emitting iridium(iii) complexes for mitochondrial imaging in living cells

Abstract

Biocompatible transition metal complexes dyes emitting in the near-infrared (NIR) region, are highly desirable in fluorescence imaging techniques. However, a high-performance mitochondria-specific labeling NIR probe with high photostability is still lacking. Herein we reported two NIR-emitting cationic iridium(iii) complexes [Ir(pbq-g)(N^N)]Cl (pbq-g = phenylbenzo[g]-quinoline; N^N = 2-(1-benzyl-1H-pyrazol-3-yl) pyridine (Ir1) and 2-(1-(naphthalen-1-ylmethyl)-1H-pyrazol-3-yl) pyridine (Ir2)). These two novel Ir(iii) complexes with different N^N ligands exhibited similar NIR emission with λ at 751 nm for Ir1 and 750 nm for Ir2 in PBS solution, with luminescence quantum yields of around 0.62 for Ir1 and 0.85 for Ir2. These two complexes showed high mitochondrial specificity, superior photostability, high resistance to the loss of the mitochondrial membrane potential and appreciable tolerance to environmental changes, allowing NIR imaging of mitochondrial morphological changes over long periods of time. These excellent photophysical and imaging properties made them promising NIR luminescent tags for applications in bioimaging.

Facile Synthesis of an Organic Solid State Near-Infrared-Emitter with Large Stokes Shift via Excited-State Intramolecular Proton Transfer

“…9,11 In the literature, there are only a limited group of compounds reported as NIR emitters, which largely include certain organic dyes and their derivatives such as cyanines, 2 phthalocyanines, 14 squarines, 15 BODIPYs, 16 rhodamines, 17 porphyrinoids, 18 as well as a number of donor–acceptor chromophores 1 and some rare-earth and transition metal complexes. 19,20 However, many of such compounds require difficult and expensive synthetic procedures. Therefore, the development of new classes of organic solid-state NIR emitters that can be crafted easily from simple building blocks is of utmost relevance.…”

Recent Advances on Metal-Based Near-Infrared and Infrared Emitting OLEDs

“…There are numerous examples of heteroleptic iridium complexes with cyclometalated ligands of extended poly-aromaticity to produce NIR emitting materials in the literature. For instance, the introduction of pyrene units into a cyclometalated ligand [31] or anthracene units [80] can be cited as examples. However, all these NIR emitters have not been designed for OLEDs applications, and some of these structures have been prepared for biological applications [80].…”

Recent Progress on the Exploration of the Biological Utility of Cyclometalated Iridium(III) Complexes

“…Similar approaches to creating NIR phosphorescent labels have also been pursued. The group of Chao and Xu employed 2‐(2‐pyridyl)anthracene cyclometalating ligands to prepare cationic biscyclometalated Ir(III) complexes ( 4 in Scheme ) . Crystal structure analysis revealed a rare cis ‐ N , N disposition of two pyridyl rings in the cyclometalating ligands.…”