Synthesis, Structure, and Characterization of Chromo(fluoro)ionophores with Cation-Triggered Emission Based on N-Methylaza-Crown-Ether Styryl Dyes

Density functional theory study of crown ether-magnesium complexes: from a solvated ion to an ion trap

Metal ion detection rests on host-guest recognition. We propose a theoretical protocol for designing an optimal trap for a desired metal cation. A host for magnesium ions was sought for among derivatives of crown ethers 12-crown-4, 15-crown-5, and 18-crown-6. Mg-crown complexes and their hydrated counterparts with water molecules bound to the cation were optimized using density functional theory. Based on specific geometric criteria, Interacting quantum atoms analysis and density functional theory-based molecular dynamics of Mg-crown complexes immersed in water, crown ethers for optimal accommodation of Mg2+ in aqueous solution were identified. Selectivity of the chosen crowns towards Na+, K+, and Ca2+ ions is addressed.

Subnanomolar Detection of Mercury Cations in Water by an Interfacial Fluorescent Sensor Achieved by Ultrathin Film Structure Optimization

The objectives of this work were to develop and extend the previously proposed approaches to control the structure of nanoscale planar systems based on modular fluorophore compounds capable of efficient analyte binding and to optimize the architecture of ultrathin films formed from them to create a thin-film sensor element for mercury cations. The possibility of applying the ratiometric approach to the fluorescence measurements to obtain a quantitative analytical signal was shown. It was found that films with the Langmuir-Schaefer film architecture, in which the receptor crown ether groups of the fluoroionophore are oriented toward the studied solution, allow the quantitative determination of mercury cations in water at concentrations below the threshold limit value and are especially effective in the analyte concentration range of 10^-10-10^-5 M. High selectivity of the obtained thin-film sensitive elements with respect to mercury cations and the possibility of regeneration of such elements after quantitative determination of mercury cations in aqueous solutions are demonstrated.

Metal-Ligand Coordination Induced Ionochromism for π-Conjugated Materials

Recent studies indicated that the toxicity of heavy metal ions caused a series of environmental, food, and human health problems. Chemical ionochromic sensors are crucial for detecting these toxicity ions. Incorporating organic ligands into π-conjugated polymers made them receptors for metal ions, resulting in an ionochromism phenomenon, which is promising to develop chemosensors for metal ions. This review highlights the recent advances in π-conjugated polymers with ionochromism to metal ions, which may guide rational structural design and evaluation of chemosensors.

Rational Design of Hemicyanine Langmuir Monolayers by Cation-Induced Preorganization of Their Structure for Sensory Response Enhancement

This study takes a novel approach to the enhancement of receptor properties of thin-film sensors based on hemicyanine dyes with dithia-aza-crown-ionophoric moiety. By means of in situ UV-vis and X-ray reflectivity (XRR) measurements, it was revealed that the introduction of up to 0.25 mmol of Hg²⁺ under a preliminarily compressed monolayer, formed on pure water, does not lead to cation binding. This is due to the formation of "head-to-tail" aggregates (H-type), in which ionophoric group is blocked by the neighboring molecule. However, the presence of barium cations in the subphase under the forming Langmuir monolayer of the mentioned compound causes codirectional (head-to-head) orientation of chromoionophore fragments. This provides preorganization of a monolayer structure that facilitates the binding of complementary mercury cations, even in a compressed state: asymmetric sandwich complexes containing two dye molecules coordinate a Hg²⁺ cation between them. This complex structure was confirmed by molecular modeling based on the electron density distribution calculated from XRR measurement data. Such preorganization of supramolecular ensembles induced by cations, which do not participate in the complex formation with macroheterocyclic receptors, may have applications in fields where strict control of molecular orientation at the interface is required, such as nanoelectronics, sensorics, catalysis, etc.

Oxaazamacrocycles incorporating the quinoline moiety: synthesis and the study of their binding properties towards metal cations

Nitrogen- and oxygen-containing macrocycles with an endocyclic quinoline moiety synthesized via Pd(0)-catalyzed amination were found to be prospective fluorescent chemosensors for Cu(ii).

Supramolecular Dimerization and [2 + 2] Photocycloaddition Reactions of Crown Ether Styryl Dyes Containing a Tethered Ammonium Group: Structure-Property Relationships

Molecular self-assembly is an effective strategy for controlling the [2 + 2] photocycloaddition reaction of olefins. The geometrical properties of supramolecular assemblies are proven to have a critical effect on the efficiency and selectivity of this photoreaction both in the solid state and in solution, but the role of other factors remains poorly understood. Convenient supramolecular systems to study the structure-property relationships are pseudocyclic dimers spontaneously formed by styryl dyes containing a crown ether moiety and a remote ammonium group. New dyes of this type were synthesized to investigate the effects of structural and electronic factors on the quantitative characteristics of supramolecular dimerization and [2 + 2] photocycloaddition in solution. Variable structural parameters for the styryl dyes were the size and structure of macrocyclic moiety, the nature of heteroaromatic residue, and the length of the ammonioalkyl group attached to this residue. Quantum chemical calculations of the pseudocyclic dimers were performed in order to interpret the relationships between the structure of the ammonium dyes and the efficiency of the supramolecular photoreaction. One of the dimeric complexes was obtained in the crystalline state and studied by X-ray diffraction. The results obtained demonstrate that the photocycloaddition in the pseudocyclic dimers can be dramatically affected by the electronic structure of the styryl moieties, as dependent on the electron-donating ability of the substituents on the benzene ring, and by the conformational flexibility of the pseudocycle, which determines the mobility of the olefinic bonds. The significance of electronic factors is highlighted by the fact that the photocycloaddition quantum yield in geometrically similar dimeric structures varies from ≤10(-4) to 0.38. The latter value is unusually high for olefins in solution.

The effect of ring sizes and alkali metal cations on interaction energy, charge transfer and nonlinear optical properties of crown ether derivatives

A series of the crown ethers are designed to explore the effect of ring sizes and the nature of alkali metal cations doping on the interaction energy, charge transfer and nonlinear optical property.

N-Methylbenzoaza-18-crown-6-ether derivatives as efficient alkali metal cations sensors: the dipole moment and first hyperpolarizability

1-Li+, 1-Na+ and 1-K+ complexes formed by N-methylbenzoaza-18-crown-6-ether derivatives with one alkali metal cation were investigated. Their dipole moments and first hyperpolarizabilities take on opposite trends with increasing the atomic number.