Supramolecular Properties of a Monocarboxylic Acid-Functionalized "Texas-Sized" Molecular Box.

A new carboxylic acid-functionalized "Texas-sized" molecular box TxSB-CO2H has been prepared by combining two separate building blocks via an iodide-catalyzed macrocyclization reaction. A single-crystal X-ray diffraction analysis revealed a paired "clip-like" dimer in the solid state. Concentration-dependent behavior is seen for samples of TxSB-CO2H as prepared, as inferred from 1H NMR spectroscopic studies carried out in DMSO- d6. However, in the presence of excess acid (1% by weight of deuterated trifluoracetic acid; TFA- d1), little evidence of aggregation is seen in DMSO- d6 except at the highest accessible concentrations. In contrast, the conjugate base form, TxSB-CO2-, produced in situ via the addition of excess triethylamine to DMSO- d6 solutions of TxSB-CO2H acts as a self-complementary monomer that undergoes self-assembly to stabilize a formal oligomer ([TxSB-CO2-] n) with a degree of polymerization of approximately 5-6 at a concentration of 70 mM. Evidence in support of the proposed oligomerization of TxSB-CO2- in solution and in the solid state came from one- and two-dimensional 1H NMR spectroscopy, X-ray crystallography, dynamic light scattering (DLS), and scanning electron microscopy (SEM). A series of solution-based analyses carried out in DMSO and DMSO- d6 provide support for the notion that the self-assembled constructs produced from TxSB-CO2- are responsive to environmental stimuli, including exposure to the acetate anion (as its tetrabutylammonium, TBA+, salt), and changes in overall concentration, temperature, and protonation state. The resulting transformations are thought to reflect the reversible nature of the underlying noncovalent interactions. They also permit the stepwise interconversion between TxSB-CO2H and [TxSB-CO2-] n via the sequential addition of triethylamine and TFA- d1. The present work thus serves to illustrate how appropriately functionalized molecular box-type macrocycles may be used to develop versatile stimuli-responsive materials. It also highlights how aggregated forms seen in the solid state are not necessarily retained under competitive solution-phase conditions.

Physical Removal of Anions from Aqueous Media by Means of a Macrocycle-Containing Polymeric Network.

Reported here is a hydrogel-forming polymer network that contains a water-soluble tetracationic macrocycle. Upon immersion of this polymer network in aqueous solutions containing various inorganic and organic salts, changes in the physical properties are observed that are consistent with absorption of the constituent anions into the polymer network. This absorption is ascribed to host-guest interactions involving the tetracationic macrocyclic receptor. Removal of the anions may then be achieved by lifting the resulting hydrogels out of the aqueous phase. Treating the anion-containing hydrogels with dilute HCl leads to the protonation-induced release of the bound anions. This allows the hydrogels to be recycled for reuse. The present polymer network thus provides a potentially attractive approach to removing undesired anions from aqueous environments.

Design and synthesis of triazolyl coumarins as Hg2+ selective fluorescent chemosensors.

A series of triazolyl coumarin derivatives L1-L4, with and without spacer groups between the coumarin and the triazole groups, were synthesized as fluorescent sensors to study their binding ability and selectivity toward metal ions. Ligand L3, which contains an acetyl linker between the triazole and the coumarin, exhibited a high selectivity toward Hg(2+) in polar protic solvents MeOH-CHCl(3) (9 : 1, v/v) with fluorescent enhancement, furthermore, it was found to bind two Hg(2+) at a high concentration (>12.5 mM) of Hg(ClO(4))(2). In contrast, L4, in which position 4 of the triazole unit was replaced by a benzyl group instead of the 4-tert-butylphenoxymethyl group used in L1-L3, showed a binding stoichiometry toward only one Hg(2+). On the basis of the fluorescent sensing, IR, and (1)H NMR titration results of ligands L1-L4, we proposed that not only the acetyl C=O but also the ether group of the 4-tert-butylphenoxymethyl of assisted the triazole nitrogen atoms in the complexation of Hg(2+) to form a 1 : 2 complex (L3·(Hg(2+))(2)).

N-1- and N-2-anthryl succinimide derivatives: C-N bond rotational behaviors and fluorescence energy transfer.

New rigid bicyclic N-anthrylsuccinimide 1a, 1b, 2a, and 2b were prepared. The C(aryl)-N(imide) bond rotational barriers, intra/intermolecular arene-arene interactions, and photophysical properties were investigated. The rotational behaviors are more significantly controlled by the position of C(aryl)-N(imide) connection than the sidewall framework. The fluorescence energy transfer (Φ(ET)) in 1a and 1b was estimated to be 61% and 53%, respectively. The difference is attributed to the position of C(aryl)-N(imide) connection, which directly influences the relative orientation of donor (naphthalene) and acceptor (anthracene).

Encoding, Reading, and Transforming Information Using Multifluorescent Supramolecular Polymeric Hydrogels.

Traditional (1D, 2D, and 3D) codes are widely used to provide convenient readouts of encoded information. However, manipulating and transforming the encoded information is typically difficult to achieve. Here, the preparation of three fluorescent (blue, green, and red) hydrogels containing both tetracationic receptor-anion recognition motifs and gel-specific fluorophores is reported, which may be used as building blocks to construct through physical adhesion fluorescent color 3D codes (Code A, Code B, and Code C) that may be read out by a smartphone. As a result, parts of the individual gel components that make up Code B can be replaced with other gel building blocks to form Code A via a cut and adhesion approach. A fluorophore responsive to ammonia is further incorporated into one of the hydrogels. This allows the gel block-derived pattern that makes up Code C to be converted to Code A by chemical means. Therefore, the encoded information produced by patterns of the present hydrogels may be transformed through either physical action or by exposure to a chemical stimulus. Due to the nature of the soft materials involved, the codes can be used as wearable materials.