Anion binding induced conformational changes exploited for recognition, sensing and pseudorotaxane disassembly.

Investigations to exploit the anion binding induced conformational changes displayed by a new class of acyclic receptor for anion recognition, fluorescence sensing and pseudorotaxane disassembly are described. A series of imidazolium-appended bis-amide-pyridine, pyridine N-oxide and pyridinium containing receptors are synthesised and their anion binding properties elucidated using (1)H NMR spectroscopy. Upon anion recognition, the receptors exhibit a substantial conformational change from an 'open' to a more 'closed' intramolecular geometry. The fluorescence anion sensing ability of a bis-pyrene-functionalised analogue is investigated, with anion-induced responses arising from excimer signalling mechanisms. A pseudorotaxane assembly formed between the pyridine N-oxide receptor acting as a threading component and an isophthalamide macrocycle is demonstrated to undergo disassembly resulting from the conformational behaviour exhibited by the thread upon chloride binding.

Anion-templated assembly of pseudorotaxanes: importance of anion template, strength of ion-pair thread association, and macrocycle ring size.

A wide range of pseudorotaxane assemblies containing positively charged pyridinium, pyridinium nicotinamide, imidazolium, benzimidazolium and guanidinium threading components, and macrocyclic isophthalamide polyether ligands have been prepared using a general anion templation procedure. In noncompetitive solvent media, coupling halide anion recognition by a macrocyclic ligand with ion-pairing between the halide anion and a strongly associated cation provides the driving force for interpenetration. Extensive solution 1H NMR binding studies, thermodynamic investigations, and single-crystal X-ray structure determinations reveal that the nature of the halide anion template, strength of the ion-pairing between the anion template and the cationic threading component, and to a lesser extent favorable second sphere pi-pi aromatic stacking interactions between the positively charged threading component and macrocyclic ligand, together with macrocyclic ring size, affect the efficacy of pseudorotaxane formation.

Luminescent ruthenium(II) bipyridine-calix[4]arene complexes as receptors for lanthanide cations.

The synthesis and photophysical properties of novel luminescent ruthenium(II) bipyridyl complexes containing one, two, or six lower rim acid-amide-modified calix[4]arene moieties covalently linked to the bipyridine groups are reported which are designed to coordinate and sense luminescent lanthanide ions. All the Ru-calixarene complexes synthesized in this work are able to coordinate Nd(3+), Eu(3+), and Tb(3+) ions with formation of adducts of variable stoichiometry. The absorbance changes allow the evaluation of association constants whose magnitudes depend on the nature of the complexes as well as on the nature of the lanthanide cation. Lanthanide cation complex formation affects the ruthenium luminescence which is strongly quenched by Nd(3+) ion, moderately quenched by the Eu(3+) ion, and poorly or moderately increased by the Tb(3+) ion. In the case of Nd(3+), the excitation spectra show that (i) the quenching of the Ru luminescence occurs via energy transfer and (ii) the electronic energy of the excited calixarene is not transferred to the Ru(bpy)(3) but to the neodymium cation. In the case of Tb(3+), the adduct's formation leads to an increase of the emission intensities and lifetimes. The reason for this behavior was ascribed to the electric field created around the Ru calix[4]arene complexes by the Tb(3+) ions by comparison with the Gd(3+) ion, which behaves identically and can affect ruthenium luminescence only by its charge. However, especially for compounds 1 and 3, it cannot be excluded that some contribution comes from the decrease of vibrational motions (and nonradiative processes) due to the rigidification of the structure upon Tb(3+) complexation. In the case of Eu(3+), compounds 1, 2, and 4 were quenched by the lanthanide addition but the quenching of the ruthenium luminescence is not accompanied by europium-sensitized emission which suggests that an electron-transfer mechanism is responsible for the quenching. On the contrary, compound 3 exhibits enhanced emission upon addition of Eu(3+) (as nitrate salt); it is suggested that the lack of quenching in the [3.2Eu(3+)] adduct is due to kinetic reasons because the electron-transfer quenching process is thermodynamically allowed.

Halide anion directed assembly of luminescent pseudorotaxanes.

A series of new photo-active rhenium(i) bipyridyl based pseudorotaxane complexes is assembled via halide anion templation.

Anion recognition and redox sensing amplification by self-assembled monolayers of 1,1'bis(alkyl-N-amido)ferrocene.

Surface pre-organisation within robust amidoferrocene self-assembled monolayers can be exploited in the selective electrochemical sensing of anions in both organic and aqueous media.

Calix[4]arene based dendrimers.

The synthesis of calix[4]arene based dendrimers containing up to seven calix[4]arene moieties is described, including the X-ray crystal structure of a tris-calix[4]arene branching derivative.