Platinum(II) terpyridine-based supramolecular polymer gels with induced chirality.

Metal-ligand binding plays a crucial role in regulating the photophysical properties of supramolecular gels. In this study, we designed 1-Pt complexes comprising a central benzene-1,3,5-tricarboxamide unit functionalized with three terpyridines, which can form supramolecular gels with Pt(II). The resulting supramolecular gel of 1-Pt exhibited strong orange emission, which was attributed to the metal-to-metal ligand charge transfer during gel formation. Furthermore, the temperature-dependent absorption spectrum changes of the supramolecular polymer 1-Pt exhibited a nonsigmoidal transition, following a cooperative pathway involving a nucleation-elongation mechanism. Additionally, the strategy for the co-assembling system involving 1-Pt with chiral molecules (D-form and L-form) induced the helical arrangement of 1-Ptvia chiral additives in supramolecular metallogels.

In Situ Supramolecular Gel Formed by Cyclohexane Diamine with Aldehyde Derivative.

Low-molecular-weight gels have great potential for use in a variety of fields, including petrochemicals, healthcare, and tissue engineering. These supramolecular gels are frequently metastable, implying that their properties are kinetically controlled to some extent. Here, we report on the in situ supramolecular gel formation by mixing 1,3-cyclohexane diamine (1) and isocyanate derivative (2) without any catalysis at room temperature in various organic solvents. A mixture of building blocks 1 and 2 in various organic solvents, dichloromethane, tetrahydrofuran, chloroform, toluene, and 1,4-dioxane, resulted in the stable formation of supramolecular gel at room temperature within 60-100 s. This gel formation was caused by the generation of urea moieties, which allows for the formation of intermolecular hydrogen-bonding interactions via reactions 1 and 2. In situ supramolecular gels demonstrated a typical entangled fiber structure with a width of 600 nm and a length of several hundred µm. In addition, the supramolecular gels were thermally reversible by heating and cooling. The viscoelastic properties of supramolecular gels in strain and frequency sweets were enhanced by increasing the concentration of a mixed 1 and 2. Furthermore, the supramolecular gels displayed a thixotropic effect, indicating a thermally reversible gel.

Pyrene-Based Co-Assembled Supramolecular Gel; Morphology Changes and Macroscale Mechanical Property.

Two pyrene derivatives having the perylenediimide (1) or the alky chain (2) in the middle of molecules were synthesized. Co-assembled supramolecular gels were prepared at different molar ratios of 0.2, 0.5, and 0.8 equiv. of 2 to 1. By SEM observation, the morphology of co-assembled supramolecular gels changed from spherical nanoparticles to three-dimensional network nanofibers as the ratio of 2 increased. In addition, the pyrene-excimer emission of co-assembled gels increased with increasing concentration of 2, and was stronger when compared with the condition without 1 or 2, indicating the formation of pyrene interaction between 1 and 2. In addition, the sol-gel transition was found to be reversible over repeated measurement by tube inversion method. The rheological properties of co-assembled supramolecular gels were also improved by increasing the ratio of 2, due to the increased nanoscale flexibility of supramolecular packing by introducing alkyl chain groups through heterogeneous pyrene interaction. These findings suggest that macroscale mechanical strength of co-assembled supramolecular gel was strongly influenced by nanoscale flexibility of the supramolecular packing.

Self-Assembled Triphenylphosphonium-Conjugated Dicyanostilbene Nanoparticles and Their Fluorescence Probes for Reactive Oxygen Species.

We report self-assembled novel triphenylphosphonium-conjugated dicyanostilbene-based as selective fluorescence turn-on probes for ¹O2 and ClO-. Mono- or di-triphenylphosphonium-conjugated dicyanostilbene derivatives 1 and 2 formed spherical structures with diameters of ca. 27 and 56.5 nm, respectively, through π-π interaction between dicyanostilbene groups. Self-assembled 1 showed strong fluorescent emission upon the addition of ¹O2 and ClO- compared to other ROS (O2-, •OH, NO, TBHP, H2O2, GSH), metal ions (K⁺, Na⁺), and amino acids (cysteine and histidine). Upon addition of ¹O2 and ClO-, the spherical structure of 1 changed to a fiber structure (8-nm wide; 300-nm long). Upon addition of ¹O2 and ClO-, the chemical structural conversion of 1 was determined by FAB-Mass, NMR, IR and Zeta potential analysis, and the strong emission of the self-assembled 1 was due to an aggregation-induced emission enhancement. This self-assembled material was the first for selective ROS as a fluorescence turn-on probe. Thus, a nanostructure change-derived turn-on sensing strategy for ¹O2 or ClO- may offer a new approach to developing methods for specific guest molecules in biological and environmental subjects.

Fluorescent composite hydrogels of metal-organic frameworks and functionalized graphene oxide.

GO MOFs! Azobenzoic acid functionalized graphene (A-GO) can act as a structure-directing template that influences hydrogel formation together with metal-organic frameworks (MOFs). Zn(2+) MOFs of pyridine derivatives work as framework linkers between the A-GO sheets (MOF-A-GO, see figure). MOF-A-GO exhibits a strong fluorescence enhancement upon gel formation. In addition, MOF-A-GO selectively recognizes trinitrotoluene.

Functionalized monolayers on mesoporous silica and on titania nanoparticles for mercuric sensing.

Heterogeneous "naked-eye" colorimetric and spectrophotometric cation sensors were prepared by immobilization of an azobenzene-coupled receptor onto mesoporous silica (AR-SiO(2)) or titania nanoparticles (AR-TiO(2)) via sol-gel or hydrolysis reactions. The optical sensing ability of AR-SiO(2) was studied by addition of metal ions such as K(+), Ca(2+), Sr(2+), Co(2+), Cd(2+), Pb(2+), Zn(2+), Fe(3+), Cu(2+) and Hg(2+) ions (all as chlorides) in aqueous solution. Upon the addition of Hg(2+) ion in suspension, the AR-SiO(2) resulted in a color change from yellow to deep red. No significant color changes were observed in the parallel experiments with K(+), Ca(2+), Sr(2+), Co(2+), Cd(2+), Pb(2+), Zn(2+), Fe(3+) or Cu(2+) ion. These findings confirm that the AR-SiO(2) can be useful as chemosensors for selective detection of Hg(2+) ion over a range of metal ions in aqueous solution. Also, the color change of AR-SiO(2) was independent of the presence of anions NO(3)(-), ClO(4)(-), Br(-) and I(-). We also prepared a portable chemosensor kit by coating a 4 microm thick film of AR-TiO(2) onto a glass substrate. We found that this AR-TiO(2) film detects Hg(2+) ion at pH 7.4 with a sensitivity of 28 nM. Finally, we tested the effect of pH on AR-TiO(2) with Hg(2+) ion between pH 1.0 to 11.0. The absorbance and color changes of AR-TiO(2) were almost constant between pH 4 and 11. The results imply that the AR-TiO(2) film is applicable as a portable colorimetric sensor for the detection of Hg(2+) ion in the environmental field.

Donor-set-induced coordination sphere and oxidation-state switching in the copper complexes of O2S2X (X = S, O and NH) macrocycles.

Reaction of the O(2)S(2)X-macrocycles (L(1), X = S; L(2), X = NH; and L(3), X = O) with Cu(ClO(4))(2) x 6 H(2)O affords 1:1 (M/L) square-pyramidal Cu(II) complexes when X = S and NH but yields a rare 1:2 sandwich-type tetrahedral Cu(I) complex when X = O; the X-ray structures of all three complexes are reported. Substitution of O for S or NH in the ligand structure thus results in a donor-set-induced II/I oxidation state change of the copper, and this is accompanied by a square-pyramidal to tetrahedral topological change in the solid state. Spectrophotometric titration data (including Job plots) indicate that similar behavior occurs in acetonitrile. In further experiments aimed at investigating the generality of the above redox behavior, it was shown that the 16- and 18-membered analogs of the 17-membered L(3) also induce a similar II/I redox change in acetonitrile. It was demonstrated for L(3) that the above-induced Cu(II/I) change is also maintained when the reaction solvent is changed from acetonitrile to methanol or ethanol.

Reversible solid optical sensor based on acyclic-type receptor immobilized SBA-15 for the highly selective detection and separation of Hg(II) ion in aqueous media.

An acyclic receptor immobilized mesoporous silica (ARMS) was prepared by sol-gel reaction and its optical sensing ability was studied upon the addition of heavy metal ions in aqueous solution.