Aggregation-Induced Emission-Active Ruthenium(II) Complex of 4,7-Dichloro Phenanthroline for Selective Luminescent Detection and Ribosomal RNA Imaging

Abstract

The development of red emissive aggregation-induced emission (AIE) active probes for organelle-specific imaging is of great importance. Construction of metal complex-based AIE-active materials with metal-to-ligand charge transfer (MLCT), ligand-to-metal charge transfer (LMCT) emission together with the ligand-centered and intraligand (LC/ILCT) emission is a challenging task. We developed a red emissive ruthenium(II) complex, 1[PF], and its perchlorate analogues of the 4,7-dichloro phenanthroline ligand. 1[PF] has been characterized by spectroscopic and single-crystal X-ray diffraction. Complex 1 showed AIE enhancement in water, highly dense polyethylene glycol media, and also in the solid state. The possible reason behind the AIE property may be the weak supramolecular π···π, C-H···π, and C-Cl···H interactions between neighboring phen ligands as well as C-Cl···O halogen bonding (XB). The crystal structures of the two perchlorate analogues revealed C-Cl···O distances shorter than the sum of the van der Waals radii, which confirmed the XB interaction. The AIE property was supported by scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and atomic force microscopy studies. Most importantly, the probe was found to be low cytotoxicity and to efficiently permeate the cell membrane. The cell-imaging experiments revealed rapid staining of the nucleolus in HeLa cells via the interaction with nucleolar ribosomal ribonucleic acid (rRNA). It is expected that the supramolecular interactions as well as C-Cl···O XB interaction with rRNA is the origin of aggregation and possible photoluminescence enhancement. To the best of our knowledge, this is the first report of red emissive ruthenium(II) complex-based probes with AIE characteristics for selective rRNA detection and nucleolar imaging.

Note of Caution for the Aqueous Behaviour of Metal‐Based Drug Candidates

“…Herein, we describe the water‐DMSO mixture (1 % v/v) behaviour of two ruthenium polypyridyl complexes previously reported by our group as potential chemotherapeutic agents against cancer, namely [Ru(DIP) 2 (sq)](PF 6 ) and [Ru(DIP) 2 (3‐methoxysq)](PF 6 ), where DIP is 4,7‐diphenyl‐1,10‐phenanthroline, sq=semiquinonate and 3‐methoxysq=3‐methoxysemiquinonate (Scheme ) . The formation of ruthenium polypyridyl nanoaggregates is a known phenomenon . For example, the formation of nanoaggregates of [Ru(DIP) 3 ] 2+ and [Ru(bpy) 3 ] 2+ in water was previously reported in the literature.…”

“…[7,8] The formation of ruthenium polypyridyl nanoaggregates is a known phenomenon. [9][10][11][12][13][14][15][16] For example, the formation of nanoaggregates of [Ru(DIP) 3 ] 2 + and [Ru(bpy) 3 ] 2 + in water was previously reported in the literature. However, overall, data currently available in the literature on this topic is relatively scarce.…”

Beyond Solvent Exclusion: i-Motif Detecting Capability and an Alternative DNA Light-Switching Mechanism in a Ruthenium(II) Polypyridyl Complex

“…When well dissolved, AIE probes have no or limited emission, but can emit strongly when aggregated, due to the addition of a poorly solubilising solvent, for example. 35 200 µL mixtures of acetonitrile in water (0% -90% water) and PEG-300 in water (0% PEG-300 to 90% PEG-300) were made up. For each fraction, two samples were made, one containing 2 µL cis (from a 1 mM stock of cis[PF6]2 or cis[PF6][Cl]) and one containing 2 µL acetonitrile or water.…”

Enhanced three-photon activity triggered by the AIE behaviour of a novel terpyridine-based Zn(ii) complex bearing a thiophene bridge

“…As shown in Fig. S4,† massive C–H···π interactions and hydrogen bonds within DZ1 were found, which could hinder the rotation of single bonds and activate restriction of intramolecular rotation (RIR), thereby resulting in AIE 27…”