Bright red emission with high color purity from Eu(iii) complexes with π-conjugated polycyclic aromatic ligands and their sensing applications

Eu(iii) complexes emit red light with a high color purity and have consequently attracted attention for development toward display and physical sensing applications. The characteristic pure color emission originates from the intra-4f–4f transition, and the brightness strongly depends on the electronic and steric structures of organic ligands. A large π-conjugated ligand design with a large absorption coefficient has been actively studied for achieving bright emission. The π-conjugated Eu(iii) luminophores also provide oxygen and temperature sensing properties by controlling their excited state dynamics based on π-electron systems. A comprehensive understanding of the design strategy of large π-conjugated ligands is crucial for the further development of luminescent Eu(iii) complexes. In this review, we summarize the research progress on π-conjugated Eu(iii) luminophores exhibiting bright emission and their physical sensing applications.

In this review, we summarize the research progress on π-conjugated Eu(iii) luminophores exhibiting bright emission and their physical sensing applications.

High anticancer activity and apoptosis- and autophagy-inducing properties of novel lanthanide(III) complexes bearing 8-hydroxyquinoline-N-oxide and 1,10-phenanthroline

In the quest for rare earth metal complexes with enhanced cancer chemotherapeutic properties, the discovery of seven lanthanide(iii) complexes bearing 8-hydroxyquinoline-N-oxide (NQ) and 1,10-phenanthroline (phen) ligands, i.e., [SmIII(NQ)(phen)(H2O)Cl2] (Ln1), [EuII(NQ)(phen)(H2O)Cl2] (Ln2), [GdIII(NQ)(phen)(H2O)Cl2] (Ln3), [DyIII(NQ)(phen)(H2O)Cl2] (Ln4), [HoIII(NQ)(phen)(H2O)Cl2] (Ln5), [ErIII(NQ)(phen)(H2O)Cl2] (Ln6), and [YbIII(NQ)(phen)(H2O)Cl2] (Ln7), as potential anticancer drugs is described. Complexes Ln1-Ln7 exhibit high antiproliferative activity against cisplatin-resistant A549/DDP cells (IC50 = 0.025-0.097 μM) and low toxicity to normal HL-7702 cells. Moreover, complex Ln1, and to a lesser extent Ln7, can upregulate the expression of LC3 and Beclin1 and downregulate p62 to induce apoptosis in cisplatin-resistant A549/DDP cell lines, which is related to the cell autophagy-inducing properties of Ln1 and Ln7. Furthermore, in vivo assays suggest that Ln1 significantly inhibits A549/DDP xenograft tumor growth (56.5%). These results indicate that lanthanide(iii) complex Ln1 is a promising candidate as an anticancer drug against cisplatin-resistant A549/DDP cells.

DNA Intercalating Near-Infrared Luminescent Lanthanide Complexes Containing Dipyrido[3,2-a:2',3'-c]phenazine (dppz) Ligands: Synthesis, Crystal Structures, Stability, Luminescence Properties and CT-DNA Interaction

In order to create near-infrared (NIR) luminescent lanthanide complexes suitable for DNA-interaction, novel lanthanide dppz complexes with general formula [Ln(NO₃)₃(dppz)₂] (Ln = Nd³⁺, Er³⁺ and Yb³⁺; dppz = dipyrido[3,2-a:2′,3′-c]phenazine) were synthesized, characterized and their luminescence properties were investigated. In addition, analogous compounds with other lanthanide ions (Ln = Ce³⁺, Pr³⁺, Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Tm³⁺, Lu³⁺) were prepared. All complexes were characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray diffraction analysis of the complexes (Ln = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Eu³⁺, Er³⁺, Yb³⁺, Lu³⁺) showed that the lanthanide’s first coordination sphere can be described as a bicapped dodecahedron, made up of two bidentate dppz ligands and three bidentate-coordinating nitrate anions. Efficient energy transfer was observed from the dppz ligand to the lanthanide ion (Nd³⁺, Er³⁺ and Yb³⁺), while relatively high luminescence lifetimes were detected for these complexes. In their excitation spectra, the maximum of the strong broad band is located at around 385 nm and this wavelength was further used for excitation of the chosen complexes. In their emission spectra, the following characteristic NIR emission peaks were observed: for a) Nd³⁺: ⁴F_3/2 → ⁴I_9/2 (870.8 nm), ⁴F_3/2 → ⁴I_11/2 (1052.7 nm) and ⁴F_3/2 → ⁴I_13/2 (1334.5 nm); b) Er³⁺: ⁴I_13/2 → ⁴I_15/2 (1529.0 nm) c) Yb³⁺: ²F_5/2 → ²F_7/2 (977.6 nm). While its low triplet energy level is ideally suited for efficient sensitization of Nd³⁺ and Er³⁺, the dppz ligand is considered not favorable as a sensitizer for most of the visible emitting lanthanide ions, due to its low-lying triplet level, which is too low for the accepting levels of most visible emitting lanthanides. Furthermore, the DNA intercalation ability of the [Nd(NO₃)₃(dppz)₂] complex with calf thymus DNA (CT-DNA) was confirmed using fluorescence spectroscopy.

Complexes of lanthanides(iii) with mixed 2,2′-bipyridyl and 5,7-dibromo-8-quinolinoline chelating ligands as a new class of promising anti-cancer agents

MeOMBrQ-Ho induced HeLa cell apoptosis was mediated by inhibition of telomerase activity and dysfunction of mitochondria. Remarkably, MeOMBrQ-Ho obviously inhibited HeLa xenograft tumor growth in vivo.

Photosensitized samarium(iii) and erbium(iii) complexes of planar N,N-donor heterocyclic bases: crystal structures and evaluation of biological activity

A series of Sm(iii) and Er(iii) complexes of N,N-donor heterocyclic bases were studied for their crystal structures, luminescence properties, binding with biomolecules and photo-induced DNA damage activity.

Mitochondrial selectivity and remarkable photocytotoxicity of a ferrocenyl neodymium(iii) complex of terpyridine and curcumin in cancer cells

A mixed-ligand neodymium(iii) complex of ferrocene appended terpyridine and curcumin targets the mitochondria and shows remarkable visible-light induced cytotoxicity in HeLa and MCF-7 cancer cells while being much less toxic in dark and to MCF-10A normal cells.

Luminescent europium and terbium complexes of dipyridoquinoxaline and dipyridophenazine ligands as photosensitizing antennae: structures and biological perspectives

Luminescent europium and terbium complexes of quinoxaline and phenazine ligands were studied for their structures, luminescence properties, interaction with DNA, and photo-induced DNA cleavage activity.

Lanthanide-Based Polymers with Charged Ligand Backbones: Triple-Stranded Chain Structures and their DNA Cleavage Studies

Four rare-earth metal complexes, [Ln(Ccbp)3(H2O)3]n (Ln = La (1), Ce (2), Pr (3) and Nd (4)) are synthesised from the ligand H2CcbpBr (H2CcbpBr = 4-carboxy-1-(4-carboxybenzyl)pyridinium bromide) and the respective lanthanide metal ions. Complexes 1–4 are isostructural in that every three Ccbp– ligands juxtapose two Ln3+ ions in a monodentate coordination mode to form triple-stranded one-dimensional chain structures. Each central Ln3+ atom further associates with three H2O molecules, furnishing a monocapped square-antiprism geometry. Agarose gel electrophoresis studies indicate that 1–4 are capable of cleaving DNA in the presence of H2O2, most probably via an oxidative cleavage mechanism. Complexes 1 and 2 exhibited catalytic efficiencies (kmax/KM) of 37.69 and 34.11 h–1 mM–1, and are approx. 15- and 20-fold more effective than those of complexes 3 (kmax/KM = 1.75 h–1 mM–1) and 4 (kmax/KM = 2.21 h–1 mM–1).

Coordination-perturbed single-molecule magnet behaviour of mononuclear dysprosium complexes

By changing the ratio of reactants, two mononuclear Dy complexes, [Dy(phen)(acac)(3)] (1) and [Dy(phen)(2)(NO(3))(2)(acac)]·H(2)O (2) have been synthesized and structurally characterized. In 1, a Dy atom bearing square-antiprism coordination geometry exhibits SMM behaviour, while compound 2 with a bicapped-square-antiprism geometry does not show such SMM properties. The different magnetic behaviours seen in 1 and 2 are probably due to a different coordination environment and ligand field around the Dy(III) ions. The results proved the important influence of the structural environment of a SMM on its magnetic behaviour.