A Glutathione-Responsive Short Sequence of Metal-Organic Complex Array.

A short metal-organic complex array (MOCA) containing a sequence of RPtRRu (1Cl ) was found to exhibit unique responses to a major biothiol, glutathione (GSH). Upon binding of GSH to 1Cl , the resultant 1:1 complex (1GS ) formed nanofibrous assemblies that suggested supramolecular polymerization through the double-salt-bridge structure formation. The binding behavior of this MOCA sequence to calf thymus DNA was also dependent on GSH; a larger conformational change of DNA was observed upon binding with 1GS , relative to that with 1Cl .

Halogen-Assisted Piezochromic Supramolecular Assemblies for Versatile Haptic Memory.

Sensory memory is capable of recording information and giving feedback based on external stimuli. Haptic memory in particular can retain the sensation of the interaction between the human body and the environment and help humans to describe the physical quantities in their environment and manipulate objects in daily activities. Although sensitive and accurate tactile sensors have been produced on optical and electronic devices, their rigorous operation and equipment requirements seriously limit their further applicability. In addition, their poor retainability after the removal of external stimuli also warrants further improvements. Thus, haptic memory materials, having simple structures and high sensitivity, are highly desired. Herein, we successfully developed two piezochromic assemblies assisted by halogen bonding for haptic memory. The halogen bond not only contributes to the fabrication of the network and enhances integrative stability but also broadens the natural piezofluorescent range, thus promoting sensory sensitivity. Moreover, the colorimetric change of the assemblies could be well-retained after the stimulus was removed. Upon mild heating treatment, the piezochromic response could be recovered to its original state, confirming the recyclability of this haptic memory material for use in practical applications. The present work enriches the library of piezochromic materials with enhanced performance for haptic memory.

Remarkable colorimetric sensing of heavy metal ions based on thiol-rich nanoframes.

Novel colorimetric sensors based on meso-2,3-dimercaptosuccinic acid nanoframes templated by a metal-organic framework were developed to detect heavy metal ions. Highly specific color changes in response to various heavy metal ions were employed for the easy detection and differentiation of heavy metal ions.

Synthesis of a Water-soluble Metal-Organic Complex Array.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

A water-soluble metal-organic complex array as a multinuclear heterometallic peptide amphiphile that shows unconventional anion dependency in its self-assembly.

Water-soluble metal-organic complex array 1, bearing Ru(II), Pt(II) and Rh(III) complexes at the side residues of the short peptide, exhibits anion and pH-responsive self-assembly behaviours in aqueous media. NaCl-induced aggregation of 1 at neutral pH was suppressed in phosphate buffered saline containing a mixture of Cl(-), HPO4(2-) and H2PO4(-), which is unconventional for a peptide amphiphile.

The photoirradiation induced p-n junction in naphthylamine-based organic photovoltaic cells.

The bulk heterojunction (BHJ) plays an indispensable role in organic photovoltaics, and thus has been investigated extensively in recent years. While a p-n heterojunction is usually fabricated using two different donor and acceptor materials such as poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM), it is really rare that such a BHJ is constructed by a single entity. Here, we presented a photoirradiation-induced p-n heterojunction in naphthylamine-based organic photovoltaic cells, where naphthylamine as a typical p-type semiconductor could be oxidized under photoirradiation and transformed into a new semiconductor with the n-type character. The p-n heterojunction was realized using both the remaining naphthylamine and its oxidative product, giving rise to the performance improvement in organic photovoltaic devices. The experimental results show that the power conversion efficiency (PCE) of the devices could be achieved up to 1.79% and 0.43% in solution and thin film processes, respectively. Importantly, this technology using naphthylamine does not require classic P3HT and PCBM to realize the p-n heterojunction, thereby simplifying the device fabrication process. The present approach opens up a promising route for the development of novel materials applicable to the p-n heterojunction.

A quinoxaline based N-heteroacene interfacial layer for efficient hole-injection in quantum dot light-emitting diodes.

A series of N-heterocyclic quinoxaline derivatives was successfully synthesized and applied as hole transport layers in quantum dot light-emitting diodes (QLEDs). By inducing sp(2) N-atoms into the quinoxaline backbone, the electron affinity of the obtained material was enhanced, and its optical properties and bandgap became tunable. Quinoxaline based N-heteroacenes show a narrow bandgap, high thermal stability, and aligned film morphology. The resulting N-heteroacene polymer based QLED exhibits superior performance to poly(9-vinylcarbazole) based QLED. This study presents a strategy towards the design of novel N-rich molecules for the fabrication of QLEDs with improved performance.

Macroscopic architecture of charge transfer-induced molecular recognition from electron-rich polymer interpenetrated porous frameworks.

Fluorescent and electron-rich polymer threaded into porous framework provides a scaffold for sensing acceptor molecules through noncovalent interactions. Herein, poly(9-vinylcarbazole) (PVK) threaded MIL-101 with confined nanospace was synthesized by vinyl-monomer impregnation, in situ polymerization, and interpenetration. The pore size of the resulted hybrid could be controlled by varying the time of polymerization and interpenetration. The interaction of PVK-threaded MIL-101 with guest molecules showed a charge-transfer progress with an obvious red shift in the optical spectra. Depending on the degree of the interaction, the solution color changed from blue to green or to yellow. In particular, electron-rich PVK-threaded MIL-101 could effectively probe electron-poor nitro compounds, especially 1,3,5-trinitrobenzene (TNP), a highly explosive material. This sensing approach is a colorimetric methodology, which is very simple and convenient for practical analysis and operation.

Rational Design and Synthesis of a Highly Porous Copper-Based Interpenetrated Metal-Organic Framework for High CO2 and H2 Adsorption.

Interpenetrated metal-organic frameworks (MOFs) are often observed to show lower porosity than their non-interpenetrating analogues. It would be highly desirable if the interpenetrated MOFs could still provide high stability, high rigidity, and optimal pore size for applications. In this work, an asymmetrical tricarboxylate organic linker was rationally designed for the construction of a copper(II)-based microporous MOF with a twofold interpenetrated structure of Pt3 O4 topology. In spite of having structural interpenetration, the activated MOF shows high porosity with a Brunauer-Emmett-Teller surface area of 2297 m2 g-1 , and high CO2 (15.7 wt % at 273 K and 1 bar) and H2 uptake (1.64 wt % at 77 K and 1 bar).

Frontispiece: Rational Design and Synthesis of a Highly Porous Copper-Based Interpenetrated Metal-Organic Framework for High CO2 and H2 Adsorption.

The frontispiece shows rational construction of a twofold interpenetrated metalorganic framework (MOF) with Pt3 O4 topology using an asymmetrical tricarboxylate organic linker. In spite of having structural interpenetration, the activated MOF shows high porosity along with high CO2 and H2 uptake. Details are given in the Full Paper by Ruqiang Zou and Yanli Zhao et al. page 1259.

Arsenate recognition in aqueous media by a simple tripodal urea.

The environmentally important and toxic arsenate anion (HAsO4(2-)) is trapped in the cavity of a dimeric capsular assembly formed by a tripodal urea receptor. The selective binding of HAsO4(2-) over other anions is observed in a semi-aqueous solvent using a (1)H NMR titration study.

Tris(2-aminoethyl)amine based tripodal urea receptors for oxalate: encapsulation of staggered vs. planar conformers.

Simple tris(2-aminoethyl)amine (TREN) based tripodal urea receptors are investigated for the encapsulation of divalent oxalate (C2O4(2-)) in a semi-aqueous medium. A single crystal X-ray diffraction study shows that the receptor with 3-cyanophenyl functionality captures a staggered conformer whereas the 3-fluorophenyl functionalized receptor encapsulates a less stable planar conformer.

A series of amino acid functionalized tripodal hexaamide anion receptors: ion-pair-assisted capped-cleft formation by a pentafluorophenyl-functionalized amide.

A new series of tris(2-aminoethyl)amine (tren)-based L-alanine amino acid backboned tripodal hexaamide receptors (L1-L5) with various attached moieties based on electron-withdrawing fluoro groups and lipophilicity have been synthesized and characterized. Detailed binding studies of L1-L5 with different anions, such as halides (F(-), Cl(-), Br(-), and I(-)) and oxyanions (AcO(-), BzO(-) (Bz=benzoyl), NO(3)(-), H(2)PO(4)(-), and HSO(4)(-)), have been carried out by isothermal titration calorimetric (ITC) experiments in acetonitrile/dimethylsulfoxide (99.5:0.5 v/v) at 298 K. ITC titration experiments have clearly shown that receptors L1-L4 invariably form 1:1 complexes with Cl(-), AcO(-), BzO(-), and HSO(4)(-), whereas L5 forms a 1:1 complex only with AcO(-). In the case of Br(-), I(-), and NO(3)(-), no appreciable heat change is observed owing to weak interactions between these anions and receptors; this is further confirmed by (1)H NMR spectroscopy. The ITC binding studies of F(-) and H(2) PO(4)(-) do not fit well for a 1:1 binding model. Furthermore, ITC binding studies also revealed slightly higher selectivity of this series of receptors towards AcO(-) over Cl(-), BzO(-), and HSO(4)(-). Solid-state structural evidence for the recognition of Cl(-) by this new category of receptor was confirmed by single-crystal X-ray structural analysis of the complex of tetrabutylammonium chloride (TBACl) and L1. Single-crystal X-ray diffraction clearly showed that the pentafluorophenyl-functionalized amide receptor (L1) encapsulated Cl(-) in its cavity by hydrogen bonds from amides, and the cavity of L1 was capped with a TBA cation through hydrogen bonding and ion-pair interactions to form a capped-cleft orientation. To understand the role of the cationic counterpart in solution-state Cl(-) binding processes with this series of receptors (L1-L4), a detailed Cl(-) binding study was carried out with three different tetraalkylammonium (Me(4) N(+), Et(4) N(+), and Bu(4) N(+)) salts of Cl(-). The binding affinities of these receptors with different tetralkylammonium salts of Cl(-) gave binding constants with the TBA cation in the following order: butyl>ethyl>methyl. This study further supports the role of the TBA countercation in ion-pair recognition by this series of receptors.

Anion binding in the C3v-symmetric cavity of a protonated tripodal amine receptor: potentiometric and single crystal X-ray studies.

Tris(2-aminoethyl)amine (tren) based pentafluorophenyl-substituted tripodal L, tris[[(2,3,4,5,6-pentafluorobenzyl)amino]ethyl]amine receptor is synthesized in good yield and characterized by single crystal X-ray diffraction analysis. Detailed structural aspects of binding of different anionic guests toward L in its triprotonated form are examined thoroughly. Crystallographic results show binding of fluoride in the C(3v)-symmetric cavity of [H(3)L](3+) where spherical anion fluoride is in tricoordinated geometry via (N-H)(+)···F interaction in the complex [H(3)L(F)]·[F](2)·2H(2)O, (3). In the case of complexes [H(3)L(OTs)]·[OTs](2), (4) and [H(3)L(OTs)]·[NO(3)]·[OTs], (5), tetrahedral p-toluenesulphonate ion is engulfed in the cavity of [H(3)L](3+) via (N-H)(+)···O interactions. Interestingly, complex [(H(3)L)(2)(SiF(6))]·[BF(4)](4)·CH(3)OH·H(2)O, (6) shows encapsulation of octahedral hexafluorosilicate in the dimeric capsular assembly of two [H(3)L](3+) units, via a number of (N-H)(+)···F interactions. The kinetic parameters of L upon binding with different anions are evaluated using a potentiometric study in solution state. The potentiometric titration experiments in a polar protic methanol/water (1:1 v/v) binary solvent system show high affinity of the receptor toward more basic fluoride and acetate anions, with a lesser affinity for other inorganic anions (e.g., chloride, bromide, nitrate, sulfate, dihydrogenphosphate, and p-toluenesulphonate).

Functionalized guanidinium chloride based colourimetric sensors for fluoride and acetate: single crystal X-ray structural evidence of -NH deprotonation and complexation.

A series of new symmetrically functionalized guanidinium chlorides (S1-S10) are synthesized in good yields and their sensing ability toward anions is studied in MeCN-DMF (24 : 1) (v/v). The absorption bands of these molecules in the presence of anions are tuned by varying the functional groups attached to the guanidinium moiety (which resembles urea) with respect to (i) aromaticity (S1-S4), (ii) electron induction effect (S1, S5-S9), (iii) positional isomeric effect (S7-S9), (iv) indole functionality (S10) of the conjugated aryl units. Anions that are above Cl(-) in the Hofmeister series (F(-), AcO(-), H(2)PO(4)(-)) are eligible as an analyte in this series of molecules whereas less basic anions than Cl(-) do not cause any interference. Thus, this series of molecules are suitable for the detection of anions in the narrow window of the Hofmeister series. Out of all the anions, only fluoride causes vivid colour changes from yellow to red to reddish orange and finally to blue, irrespective of the increasing aromaticity, induction and positional isomeric effect of the substituent that is attached to the guanidinium moiety. Interestingly, S9 has shown the ability to sense distinctly both F(-) and AcO(-) colourimetrically. Further S10, a sensor attached with indole functionality shows selective sensing of F(-) colourimetrically with a NIR signature at ∼930 nm though both these outputs are very unstable in nature. Stability constants for complex formation of S1-S10 (except S5) with F(-), AcO(-) are calculated by UV-vis titration experiments. Finally single crystal X-ray structural studies on the species 1 formed upon treating S6 with sodium fluoride confirms -NH deprotonation, whereas the reaction of S6 and S2 with sodium benzoate shows 1:1 host:guest binding that results in complexes 2 and 3 respectively.

Visible and near-infrared sensing of fluoride by indole conjugated urea/thiourea ligands.

Two thiourea and urea based indole conjugated ligands show selective color changes with fluoride along with an absorbance band at 936 nm and 904 nm respectively.