Square tiling by square macrocycles at the liquid/solid interface: co-crystallisation with one- or two-dimensional order.

We have systematically investigated the self-assembled monolayers of seven bimolecular mixtures of square-shaped pyridinophanes and cyclophanes bearing alkoxy or alkoxycarbonyl substituents in the presence of the tropylium ion as a marker of pyridinophanes at liquid/graphite interfaces by means of scanning tunnelling microscopy (STM). The purpose of this work was to elucidate the mixing behaviour of these macrocycles highlighting the formation of one- or two-dimensionally ordered square tilings consisting of alternating alignments of different macrocycles as a result of attractive dipole-dipole or hydrogen-bonding interactions; four co-crystals differing in the dimensionality of the ordering of pyridinophane and cyclophane were observed. The different modes of interaction between the functional groups (ether or carbonyl group) in the side-chains of the pyridinophanes and cyclophanes lead to the formation of co-crystals with dimensionally different orderings of the two macrocycles. These observations revealed that a slight modification of the molecular structure may dramatically change the mixing behaviour and structures of the co-crystals.

Aryl C-H···Cl(-) hydrogen bonding in a fluorescent anion sensor.

A new phenyl-acetylene receptor containing a carbonaceous hydrogen bond donor activates anion binding in conjunction with two stabilizing ureas. The unusual CH···Cl(-) hydrogen bond is apparent in solution by large (1)H NMR chemical shifts and by a short, linear contact in the solid state.

Synthesis and optoelectronic properties of 2,6-bis(2-anilinoethynyl)pyridine scaffolds.

A series of sixteen bisphenylureas based on a 2,6-bis(2-anilinoethynyl)pyridine scaffold have been synthesized for use as potential anion sensors. Prior work with one of these receptors revealed a distinct fluorescence response in the presence of a suitable anion source with specificity towards chloride anion. This study demonstrates that the fluorescent properties of these receptors can be tuned through the systematic variation of the pendant functional groups.

Molecular Self Assembly: Solvent Guests Tune the Conformation of a Series of 2,6-Bis(2-anilinoethynyl)pyridine-Based Ureas.

The conformations of 2,6-bis(2-anilinoethynyl)pyridine-based urea receptors were studied by single crystal X-ray diffraction methods and revealed a rich conformational flexibility influenced by solvents. Whereas receptor L(1) in DMSO prefers an "S" conformation, receptor L(1) crystallizes in an "O" conformation from DMSO/CH(3)OH binary solvent system, and a "W" conformation in the ternary solvent mixture DMSO/toluene/1,4-dioxane. In the case of L(2), the molecule adopts an "S" conformation where water molecules are sandwiched between two molecules of L(2) to form a dimer. Similar to L(2), L(3) also forms a dimer where water molecules are sandwiched between L(3) molecules, which are capped with two molecules of DMSO. Such a capping DMSO solvate is lacking in the case of L(2). Taken together, these results demonstrate that the conformation of 2,6-bis(2-anilinoethynyl) pyridine-based urea receptors can be dramatically manipulated and tuned by the choice of crystallization solvents.

Anion-dependent fluorescence in bis(anilinoethynyl)pyridine derivatives: switchable ON-OFF and OFF-ON responses.

Urea and sulfonamide derivatives of 1 exhibit ON-OFF and OFF-ON switchable fluorescent and colorimetric responses upon protonation. The magnitude of the fluorescence event is dictated by the anion, resulting in a rare, fully organic "turn-on" fluorescent sensor for chloride.

Arylethynyl receptors for neutral molecules and anions: emerging applications in cellular imaging.

This critical review will focus on the application of shape-persistent receptors for anions that derive their rigidity and optoelectronic properties from the inclusion of arylethynyl linkages. It will highlight a few of the design strategies involved in engineering selective and sensitive fluorescent probes and how arylacetylenes can offer a design pathway to some of the more desirable properties of a selective sensor. Additionally, knowledge gained in the study of these receptors in organic media often leads to improved receptor design and the production of chromogenic and fluorogenic probes capable of detecting specific substrates among the multitude of ions present in biological systems. In this ocean of potential targets exists a large number of geometrically distinct anions, which present their own problems to the design of receptors with complementary binding for each preferred coordination geometry. Our interest in targeting charged substrates, specifically how previous work on receptors for cations or neutral guests can be adapted to anions, will be addressed. Additionally, we will focus on the design and development of supramolecular arylethynyl systems, their shape-persistence and fluorogenic or chromogenic optoelectronic responses to complexation. We will also examine briefly how the "chemistry in the cuvet" translates into biological media (125 references).

Protonation activates anion binding and alters binding selectivity in new inherently fluorescent 2,6-bis(2-anilinoethynyl)pyridine bisureas.

A new class of 2,6-bis(2-anilinoethynyl)pyridine-based bisureas forms 1 : 1 complexes with halides; protonation enhances binding by over one order of magnitude, alters the binding selectivity, and provides a colorimetric indication of anion binding.