A Charge-Neutral Self-Assembled L2Zn2 Helicate as Bench-Stable Receptor for Anion Recognition at Nanomolar Concentration

The field of anion recognition chemistry is dominated by two fundamental approaches to design receptors. One relies on the formation of covalent bonds resulting in organic and often neutral host species, while the other one utilizes metal-driven self-assembly for the formation of charged receptors with well-defined nanocavities. Yet, the combination of their individual advantages in the form of charge-neutral metal-assembled bench-stable anion receptors is severely lacking. Herein, we present a fluorescent and uncharged double-stranded hydroxyquinoline-based zinc(II) helicate with the ability to bind environmentally relevant dicarboxylate anions with high fidelity in dimethyl sulfoxide (DMSO) at nanomolar concentrations. These dianions are pinned between zinc(II) centers with binding constants up to 145 000 000 M^-1. The presented investigation exemplifies a pathway to bridge the two design approaches and combine their strength in one structural motif as an efficient anion receptor.

Two Synthetic Approaches to Coinage Metal(I) Mesocates: Electrochemical versus Chemical Synthesis

We report two different approaches to isolate neutral and cationic mesocate-type metallosupramolecular architectures derived from coinage monovalent ions. For this purpose, we use a thiocarbohydrazone ligand, H₂L (1), conveniently tuned with bulky phosphine groups to stabilize the M^I ions and prevent ligand crossing to achieve the selective formation of mesocates. The neutral complexes [Cu₂(HL)₂] (2), [Ag₂(HL)₂] (3), and [Au₂(HL)₂] (4) were prepared by an electrochemical method, while the cationic complexes [Cu₂(H₂L)₂](PF₆)₂ (5), [Cu₂(H₂L)₂](BF₄)₂ (6), [Ag₂(H₂L)₂](PF₆)₂ (7), [Ag₄(HL)₂](NO₃)₂ (8), and [Au₂(H₂L)₂]Cl₂ (9) were obtained by using a metal salt as the precursor. All of the complexes are neutral or cationic dinuclear mesocates, except the silver nitrate derivative, which exhibits a tetranuclear cluster mesocate architecture. The crystal structures of the neutral and cationic copper(I), silver(I), and gold(I) complexes allow us to analyze the influence of synthetic methodology or the counterion role on both the micro- and macrostructures of the mesocates.

Regulatable Detection of Antibiotics Based on a Near-IR-Luminescent Tubelike Zn(II)-Yb(III) Nanocluster

A tubelike Zn(II)-Yb(III) cluster, [Zn6Yb5L5(HL)(NO3)4(DMF)6(EtOH)4(H2O)4] (1; DMF = N,N-dimethylformamide and EtOH = ethanol; molecular size 1.5 × 1.8 × 2.9 nm), was synthesized from a new long-chain Schiff base ligand. 1 exhibits a regulatable near-IR-luminescent response to nitrofuran antibiotics (NFAs) and fluoroquinolones with high sensitivity, which is not influenced by other antibiotics. The quenching constants of NFAs and fluoroquinolones range from 0.55 × 104 to 8.8 × 104 M-1, and the detection limits of 1 to them are from 4.2 × 10-4 to 2.6 × 10-5 M. It also shows a luminescent response to real antibiotic drugs containing NFAs and fluoroquinolones.

Ratiometric fluorescent detection of dipicolinic acid as an anthrax biomarker based on a high-nuclearity Yb18 nanoring

An 18-metal lanthanide nanoring [Yb₁₈(L¹)₈(HL²)₂(OAc)₂₀(MeOH)₈(EtOH)₆(H₂O)₄] (1), which shows a ratiometric fluorescent response to DPA, was constructed through the strategy of using two types of polydentate organic ligands. The addition of DPA increases the visible ligand-centered emission, but decreases the NIR lanthanide luminescence of 1. The limit of luminescent detection of 1 for DPA is 1.5 μM. The high fluorescence sensitivity of 1 to DPA is not affected by the existence of interferents such as aromatic carboxylates and ions.

Recent Advances of Near-Infrared (NIR) Emissive Metal Complexes Bridged by Ligands with N- and/or O-Donor Sites

Near-infrared (NIR) emissive metal complexes have shown potential applications in optical communication, chemosensors, bioimaging, and laser and organic light-emitting diodes (OLEDs) due to their structural tunability and luminescence stability. Among them, complexes with bridging ligands that exhibit unique emission behavior have attracted extensive interests in recent years. The target performance can be easily achieved by NIR light-emitting metal complexes with bridging ligands through molecular structure design. In this review, the luminescence mechanism and design strategies of NIR luminescent metal complexes with bridging ligands are described firstly, and then summarize the recent advance of NIR luminescent metal complexes with bridging ligands in the fields of electroluminescence and biosensing/bioimaging. Finally, the development trend of NIR luminescent metal complexes with bridging ligands are proposed, which shows an attractive prospect in the field of photophysical and photochemical materials.

Construction of a 18-Metal Neodymium(III) Nanoring with NIR Luminescent Sensing to Antibiotics

One 18-metal Nd(III) nanoring, [Nd₁₈(L¹)₈(HL²)₂(OAc)₂₀(MeOH)₈(EtOH)₆(H₂O)₄]·2(MeOH)·6(H₂O) (1), was constructed by the use of a hexadentate Schiff base ligand. For 1, the near-infrared (NIR) luminescence of Nd(III) was detected under the excitation of absorption band at 371 nm. The study of luminescent sensing properties exhibits that, even with the existence of other antibiotics, this Nd(III) nanoring displays high sensitivity and selectivity to nitrofuran antibiotics (NFAs). The luminescence quenching constants and limits of detection of 1 to NFAs are found to be 1.4 × 10⁴ to 3.5 × 10⁴ M^-1 and 0.9-2.2 μM, respectively.

One High-Nuclearity Cd(II)-Yb(III) Nanoring with Near-IR Luminescent Sensing to Antibiotics

One 12-metal Cd(II)-Yb(III) nanoring, [Cd₈Yb₄L₈(OAc)₈]·4OH (1), with a size of 1.2 × 2.8 × 2.8 nm was obtained from a designed flexible salen-type ligand that has eight coordination sites (O and N atoms). The near-IR emission of Yb(III) at 983 nm was detected upon the excitation of ligand-central absorption at 386 nm. This Cd(II)-Yb(III) nanoring exhibits high sensitivity to nitrofuran antibiotics (NFAs) even in the presence of other antibiotics. The quenching constants and limits of detection of NFAs are 2.5 × 10⁴-4.5 × 10⁴ M^-1 and 1.5-2.8 μM, respectively.

Construction of a High-Nuclearity Elliptical Yb(III) Nanoring: NIR Luminescent Response to Metal Ions and Nitro Explosives

One 14-metal Yb(III) nanoring [Yb₁₄(HL)₂L₂₀(DMF)₈(H₂O)₈] (1) with a size of about 1.1 × 2.5 × 2.7 nm was synthesized from a tridentate ligand. Under the excitation of ligand absorption bands, 1 exhibits the NIR luminescence of Yb(III) and displays high luminescence sensitivity and selectivity to Co(II), Cu(II), and 2,4,6-trinitrophenol (PA) at the parts per million level. The K_SV values of 1 to Co(II), Cu(II), and PA are 6.0 × 10⁴ M^-1, 3.8 × 10⁴ M^-1, and 6.9 × 10⁴ M^-1, respectively. 1 exhibits high luminescent sensitivity to PA even in the presence of other explosives.

Water-Soluble Chemical Vapor Detection Enabled by Doctor-Blade-Coated Macroporous Photonic Crystals

Water-soluble chemicals, involving a wide range of toxic chemicals in aqueous solutions, remain essential in both daily living or industrial uses. However, most toxicants are evaporated with water through their use and thus cause deleterious effects on the domestic environment and health in humans. Unfortunately, most current low-dose chemical vapor detection technologies are restricted by the use of sophisticated instruments and unable to promptly detect the quantity of diverse toxicants in a single analysis. To address these issues, this study reports the development of simple and fast chemical vapor detection using doctor-blade-coated macroporous poly(2-hydroxyethyl methacrylate)/poly(ethoxylated trimethylolpropane triacrylate) photonic crystals, in which the poly(2-hydroxyethyl methacrylate) has strong affinity to insecticide vapor owing to a favorable Gibbs free energy change for their mixing. The condensation of water-soluble chemical vapor therefore results in a significant reflection peak shift and an obvious color change. The visual colorimetric readout can be further improved by increasing the lattice spacing of the macroporous photonic crystals. Furthermore, the dependence of the reflection peak position on vapor pressure under actual conditions and the reproducibility of vapor detecting are also evaluated in this study.

Construction of 14-metal lanthanide nanorings with NIR luminescence response to ions

Two 14-metal lanthanide nanorings [Ln14(HL)2L20(DMF)8(H2O)8] (Ln = Nd(1) and Gd(2)) were constructed from a tridentate ligand. 1 displays NIR luminescence sensing properties towards metal cations and anions, especially Cu2+, Co2+, H2PO4- and F- at a ppm level.