Search Results (9)

Perylene bisimide derivatives are typical n-type semiconductors as well as redox-active materials. However, it has been difficult to produce thin films by solution processes because of their low solubilities in organic solvents. Perylene bisimide derivatives bearing oligosiloxane moieties exhibit columnar phases over wide temperature ranges, including room temperature and high solubilities in organic solvents. The columnar phases are stabilized by nanosegregation between crystal-like one-dimensional π-stacks and liquid-like mantle consisting of oligosiloxane moieties. The electron mobility at room temperature exceeded 0.1 cm²V⁻¹s⁻¹ in the ordered columnar phases of perylene bisimide derivatives bearing four disiloxane chains. Uniaxially aligned thin films of the perylene bisimide derivatives bearing oligosiloxane moieties could be produced by a spin-coating method. The spin-coated films of the perylene bisimide derivatives bearing cyclotetrasiloxane rings could be insolubilized via in situ ring-opening polymerization by the exposure of the thin films to trifluoromethanesulfonic acid vapors. Uniaxially aligned thin films of perylene bisimide derivatives bearing an ethylene oxide chain as well as cyclotetrasiloxane rings could be doped in an aqueous solution of sodium dithionate, resulting in an anisotropic electrical conductivity. Polymerized thin films of perylene bisimide derivatives bearing a crown ether ring exhibited electrochromism in electrolyte solutions. These compounds formed 1:1 complexes with lithium triflate, exhibiting columnar phases at room temperature. The nanostructures of the complexes were stabilized by the electrostatic interaction between cationic crown-metal units and triflate anions. Full article

A comparison of properties of clips based on diazacrown-n ethers (n = 4, 5, 6) as a central fragment and pendant p-tert-butylcalix[4]arenes was carried out. The clip with diaza-12-crown-4 demonstrates high selectivity towards Rb cations, the clip with diaza-15-crown-5 ether is a selective ligand for Cs cations in the alkali metal series. Clip based on diaza-18-crown-6 is a selective for Ba cations in the alkaline earth metal series. Transition metal cation clips with diaza-12-crown-4 or diaza-18-crown-6 are capable of forming predominantly 1:1 complexes. For diaza-15-crown-5 ether, the formation of 1:2 (L:M) complexes with Ni²⁺, Mn²⁺, Fe³⁺ and Pb²⁺ is observed. Full article

The analysis of time-resolved S₁–S_n absorption spectra in the 0–500 ps range, together with quantum-chemical calculations, uncovered a photorecoordination reaction for the following complexes of CD6 (a bis(aza-18-crown-6)-containing dienone (ketocyanine dye) with a central cyclohexanone fragment): CD6·(Mⁿ⁺)₂ (M = Ba²⁺, Sr²⁺, Ca²⁺, K⁺). This process takes place over hundreds of fs and involves an “axial-to-equatorial” conformational change, with the solvation shell undergoing rearrangement as well. The characteristic photorecoordination times were found to correlate with the stability constants of the complexes. The lifetimes for the fluorescent states of CD6 and its complexes, namely CD6·(Mⁿ⁺)₂ (M = Ba²⁺, Sr²⁺, Ca²⁺, K⁺), are different; ergo, there is no photoejection of crowned cations into the solution. The calculated conformational profiles in the ground and excited states indicate the presence of an energy barrier in this process. A general photorelaxation pathway is suggested for CD6·(Mⁿ⁺)₂ metal complexes (M = Ba²⁺, Sr²⁺, Ca²⁺, K⁺). The coordination of cations via the carbonyl moiety in the dye molecule promotes photorecoordination of metal cations in the cavities of the azacrown ether fragment. Photorecoordination times were found to correlate with the degree of conjugation between the lone pairs in the N atoms of the aza-18-crown-6 ether and the π subsystem in the dye molecules (established for the CD4–CD6 metal–dye complex series, where CD4 and CD5 are related dyes with central cyclobutanone and cyclopentanone fragments, respectively). Full article

A convenient method for obtaining a new type of molecular clips based on diazacrown or diamino-dibenzocrown ethers with two calixarene molecules attached to a central fragment using an amide bond was developed. Clip 1, based on diaza-18-crown-6, demonstrates exceptional selectivity toward barium in the alkaline earth metal series and forms 2:1 (L:M) complexes with copper and iron cations. With sodium and magnesium cations, clip 2, based on diamido-dibenzo-18-crown-6, forms 1:2 (L:M) complexes. The same compound interacts with cations of copper, iron, and cadmium to form 1:1 complexes with low stability constant values. Full article

Positively charged metal–ammonia complexes are known to host peripheral, diffuse electrons around their molecular skeleton. The resulting neutral species form materials known as expanded or liquid metals. Alkali, alkaline earth, and transition metals have been investigated previously in experimental and theoretical studies of both the gas and condensed phase. This work is the first ab initio exploration of an f-block metal–ammonia complex. The ground and excited states are calculated for Th^0–3+ complexes with ammonia, crown ethers, and aza-crown ethers. For Th³⁺ complexes, the one valence electron Th populates the metal’s 6d or 7f orbitals. For Th^0–2+, the additional electrons prefer occupation of the outer s- and p-type orbitals of the complex, except Th(NH₃)₁₀, which uniquely places all four electrons in outer orbitals of the complex. Although thorium coordinates up to ten ammonia ligands, octa-coordinated complexes are more stable. Crown ether complexes have a similar electronic spectrum to ammonia complexes, but excitations of electrons in the outer orbitals of the complex are higher in energy. Aza-crown ethers disfavor the orbitals perpendicular to the crowns, attributed to the N-H bonds pointing along the plane of the crowns. Full article

Unnatural amino acids with enhanced properties, such as increased complexing ability and luminescence, are considered to be highly attractive building blocks for bioinspired frameworks, such as probes for biomolecule dynamics, sensitive fluorescent chemosensors, and peptides for molecular imaging, among others. Therefore, a novel series of highly emissive heterocyclic alanines bearing a benzo[d]oxazolyl unit functionalized with different heterocyclic π-spacers and (aza)crown ether moieties was synthesized. The new compounds were completely characterized using the usual spectroscopic techniques and evaluated as fluorimetric chemosensors in acetonitrile and aqueous mixtures in the presence of various alkaline, alkaline-earth, and transition metal ions. The different crown ether binding moieties as well as the electronic nature of the π-bridge allowed for fine tuning of the sensory properties of these unnatural amino acids towards Pd²⁺ and Fe³⁺, as seen by spectrofluorimetric titrations. Full article

A family of unusual octacopper cage methylsilsesquioxanes 1–4 were prepared and characterized. Features of their cagelike (prismatic) structure were established using X-ray diffraction studies. Effects of distortion of prismatic cages 1–4 due to variation of (i) additional alkaline metal ions (K, Rb, or Cs), (ii) combination of solvating ligands, and (iii) nature of encapsulating species were found. Opportunities for the design of supramolecular 1D extended structures were found. These opportunities are based on (i) formate linkers between copper centers (in the case of Cu₈K₂-based compound 2) or (ii) crown ether-like contacts between cesium ions and siloxane cycles (in the case of Cu₈Cs₂-based compound 4). Cu₈Cs₂-complex 4 was evaluated in the catalysis of alkanes and alcohols. Complex 4 exhibits high catalytic activity. The yield of cyclohexane oxidation products is 35%. The presence of nitric acid is necessary as a co-catalyst. The oxidation of alcohols with the participation of complex 4 as a catalyst and tert-butyl hydroperoxide as an oxidizer also proceeds in high yields of up to 98%. Full article

Nitrobenzofurazan derivatives are well known for their fluorescence, whilst crown ethers are known for their complexing capacity toward cationic species. In this study, we present the synthesis and structural characterization of a new derivative containing both nitrobenzofurazan moieties and a crown ether core. The new compound was obtained from dibenzo-18-crown-6 ether, which was first nitrated, reduced to the corresponding amine, and subsequently derivatized with NBD. Structural analyses performed by IR, NMR, UV–Vis, and MS confirmed its structure and physico-chemical behavior toward the complexation of alkaline cations. Full article

Cyclic organic compounds with several ether linkages in their structure are of much concern in our daily life applications. Crown ethers (CEs) are generally heterocyclic and extremely versatile compounds exhibiting higher binding affinity. In recent years, due to their unique structure, crown ethers are widely used in drug delivery, solvent extraction, cosmetics manufacturing, material studies, catalysis, separation, and organic synthesis. Beyond their conventional place in chemistry, this review article summarizes the synthesis, biological, and potential pharmacological activities of CEs. We have emphasized the prospects of CEs as anticancer, anti-inflammatory, antibacterial, and antifungal agents and have explored their amyloid genesis inhibitory activity, electrochemical, and potential metric sensing properties. The central feature of these compounds is their ability to form selective and stable complexes with various organic and inorganic cations. Therefore, CEs can be used in gas chromatography as the stationary phase and are also valuable for cation chromatographic to determine and separate alkali and alkaline-earth cations. Full article