Changing Mechanical Strength in Cr(III)- Metallosupramolecular Polymers with Ligand Groups and Light Irradiation

Masking Strategy Constructed Metal Coordination Hydrogels with Improved Mechanical Properties for Flexible Electronic Sensors

Metal coordination hydrogels (MC-HGs) that introduce dynamically coordinate bonds together with metal ionic conduction have attracted considerable attention in flexible electronics. However, the traditional soaking method alleged to have technical scalability faces the challenge of forming MC-HGs with a "core-shell" structure, which undoubtedly reduces the whole mechanical properties and ionic stimulation responsiveness required for flexible electronics materials. Herein, a novel strategy referred to as "masking" has been proposed based on the theory of the valence bond and coordination chemistry. By regulating the masking agents and their concentrations as well as pairing mode with the metal ions, the whole mechanical properties of the resulting composites (MC-HGsMasking) show nearly double the values of their traditional soaking samples (MC-HGsSoaking). For example, the fracture stress and toughness of Fe-HGsMasking(SA, 5.0 g/L) are 1.55 MPa and 2.14 MJ/m3, almost twice those of Fe-HGsSoaking (0.83 MPa and 0.93 MJ/m3, respectively). Microstructure characterization combined with finite element analysis, molecular dynamics, and first-principles simulations demonstrates that the masking strategy first facilitating interfacial permeation of metal complexes and then effective coordination with functional ligands (carboxylates) of the hydrogels is the mechanism to strengthen the mechanical properties of composites MC-HGsMasking, which has the potential to break through the limitations of current MC-HGs in flexible electronic sensor applications.

Synthesis and crystal structure of catena-poly[[tetra-μ-acetato-copper(II)]-μ-6-eth-oxy-N 2,N 4-bis-[2-(pyridin-2-yl)eth-yl]-1,3,5-triazine-2,4-di-amine]

The title compound, [Cu2(C19H23N7O)(C2H3O2)4] n , was obtained via reaction of copper(II) acetate with the coordinating ligand, 6-eth-oxy-N 2,N 4-bis-[2-(pyridin-2-yl)eth-yl]-1,3,5-triazine-2,4-di-amine. The crystallized product adopts the monoclinic P21/c space group. The metal core exhibits a paddle-wheel structure typical for dicopper tetra-acetate units, with triazine and pyridyl nitro-gen atoms from different ligands coordinating to the two axial positions of the paddle wheel in an asymmetric manner. This forms a coordination polymer with the segments of the polymer created by the c-glide of the P21/c setting of the space group. The resulting chains running along the c-axis direction are held together by intra-molecular N-H⋯O hydrogen bonding. These chains are further packed by dispersion forces, producing an extended three-dimensional structure.

Di(2-picolyl)amine-functionalized poly(ethylene glycol) hydrogels with tailorable metal–ligand coordination crosslinking

A new class of metallo-hydrogels has been developed using di(2-picolyl)amine (DPA)-functionalized 4-arm polyethylene glycol (4A-PEG-DPAn) polymers crosslinked by metal–ligand coordination.

Generating Photonastic Work from Irradiated Dyes in Electrospun Nanofibrous Polymer Mats

For solar-driven macroscopic motions, we assert that there is a local heating that facilitates large-scale deformations in anisotropic morphologic materials caused by thermal gradients. This report specifically identifies the fate of heat generation in photonastic materials and demonstrates how heat can perform work following excitation of a nonisomerizing dye. Utilizing the electrospinning technique, we have created a series of anisotropic nanofibrous polymer mats that comprise nonisomerizing dyes. Polymers are chosen because of their relative glass transition temperatures, elastic moduli, and melting temperatures. Light irradiation of these polymer mats with an excitation wavelength matching the absorption characteristics of the dye leads to macroscopic deformation of the mat. Analysis of still images extracted from digital videos provides plots of angular displacement vs power. The data were analyzed in terms of a photothermal model. Analyses of scanning electron microscopy micrographs for all samples are consistent to local melting in low T_g polymers and softening in high T_g polymers. Dynamic mechanical analysis allowed for quantification of the modulus change under a given light fluence. We employ these data to calculate a energy conversion efficiency. These efficiencies for the polymer mats are compared to other nonmuscular systems, including a few natural, biological samples.

Programmable Mechanical Properties from a Worm Jaw-Derived Biopolymer through Hierarchical Ion Exposure

Mechanisms of biomaterial sclerotization in natural systems promise new insights into how the mechanical properties of engineered materials may be dynamically modulated. One such example involves the proteinaceous jaw of the marine sandworm, Nereis virens. Previously, the mechanical properties of the N. virens jaw were shown to be modulated by Zn binding, a property that was proposed to be enabled by the presence of the histidine-rich jaw protein, Nvjp-1. Here we demonstrate the creation of Nvjp-1-based hydrogels and show that progressive sclerotization of these hydrogels can be accomplished with hierarchical exposure to metal cations and anions. Divalent Zn cations are capable of reversibly sclerotizing the hydrogels through the formation of coordinate cross-links, an effect that is shown to be remarkably specific for Zn. Additionally, the degree of Zn-induced sclerotization is strongly influenced by the identity of the anion present in the hydrogel. Thus, the viscoelastic properties of Nvjp-1 hydrogels can be modulated through programmed, hierarchical exposure to specific cations and anions present in the sclerotizing salts. These observations have resulted in new hydrogel capabilities, such as the creation of anion-controlled shape-memory polymers, and will add to the number of control parameters that can be used to tune the properties of functional hydrogels in a dynamic manner.

Synthesis of a metal-coordinated N-substituted polybenzimidazole pyridine sulfone and method for the nondestructive analysis of thermal stability

N-substituted metal-coordinated cross-linking polybenzimidazole pyridine sulfone, as novel class of high-performance functional polymers, has been obtained by the coordination of N-substituted polybenzimidazole pyridine sulfone (Py-N-PBIS) ligand with varying content of metallic ion (Co2+, Ni2+, Zn2+). The structures of the polymers are characterized by means of fourier transform infrared spectroscopy (FT-IR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy, the results show good agreement with the proposed structures. Thermogravimetric analysis measurements exhibit that the metal coordination polymers possess good thermal stability with high thermal decomposition temperature (thermally stable up to 405–510°C). More importantly, the thermal decomposition temperature of Py-N-PBIS-(Co2+, Ni2+, Zn2+) can be nondestructively detected by taking advantage of the fluorescence quenching effect of metal coordination to 2,6-Bis(2-benzimidazolyl)pyridine structure.

Luminescent complexes made from chelating isocyanide ligands and earth-abundant metals

In this invited frontier article, recently discovered d⁶ and d¹⁰ complexes with long-lived metal-to-ligand charge transfer (MLCT) excited states are highlighted. Chelating diisocyanide ligands give access to emissive Mo(0) and Cr(0) complexes with d⁶ electron configuration exhibiting photophysical properties similar to those of Ru(ii) polypyridines or cyclometalated Ir(iii) complexes. With Ni(0), these ligands yield luminescent tetrahedral d¹⁰ complexes similar to isoelectronic Cu(i) bis(diimine) compounds.

Thermo- and redox-responsive dendronized polymer hydrogels

Unique supramolecular coordination of Fe²⁺ with terpyridine afford these hydrogels redox-responsive sol–gel transitions, while characteristic thermoresponsive properties from OEG-based first generation dendronized polymers render these hydrogels thermally-induced macroscopical volume changes and enhanced mechanical properties.

Metal-coordination crosslinked N-polyindoles as recyclable high-performance thermosets and nondestructive detection for their tensile strength and glass transition temperature

Metal coordination crosslinking between stiff N-polyindole chains was constructed, and the crosslinked films exhibited high tensile strength, high heat resistance and excellent polar solvent resistance.

Photoswitchable transition metal complexes with azobenzene-functionalized imine-based ligands: structural and kinetic analysis

We report on the characterization of two imine type ligands containing photoresponsive azobenzene units as side groups and their transition metal ions complexes.

Facile synthesis of recyclable Zn(ii)-metallosupramolecular polymers and the visual detection of tensile strength and glass transition temperature

A series of recyclable crosslinked Zn(ii)-metallosupramolecular coordination polymers are successfully achieved, of which tensile strength and T_g could be visually detected.

Rubber-elasticity and electrochemical activity of iron(ii) tris(bipyridine) crosslinked poly(dimethylsiloxane) networks

2,2'-Bipyridine-terminated poly(dimethylsiloxane)s (bpyPDMS) with number average molecular weights, M_N, of 3300, 6100, 26 200, and 50 000 g mol^-1 were synthesized. When mixed with Fe(BF₄)₂ at low concentrations, red solutions formed with UV-vis spectra that match those of iron(ii) tris(2,2'-bipyridine) (Fe(bpy)₃²⁺). Upon solvent evaporation, Fe(bpy)₃²⁺ crosslinked PDMS networks (bpyPDMS/Fe(ii)) formed, and were studied using oscillating shear rheometry. The shear storage moduli (0.084 to 2.6 MPa) were found to be inversely proportional to the M_N of the PDMS, though the storage moduli at low molecular weights greatly exceeded the storage moduli of comparable covalently crosslinked PDMS networks. The shear storage moduli exhibited the characteristic rubbery plateau up to ∼135 °C. Films of bpyPDMS/Fe(ii) coated onto electrodes were found to be electrochemically active, especially so when the PDMS M_N is low. The Fe(bpy)₃²⁺ crosslinks can be reversibly oxidized over ∼500 nm away from the electrode surface in the presence of a suitable electrolyte.