Colorimetric solvent indicators based on Nafion membranes incorporating nickel(II)-chelate complexes

Vapochromic behaviour of a nickel(II)-quinonoid complex with dimensional changes between 1D and higher

The nickel(ii)-chloranilato complex {Ni(ca)(VM)2}n (H2ca = chloranilic acid, VM = coordinated vapour molecules, such as water) shows reversible vapochromism upon exposure to various vapours and subsequent drying by heating. In contrast to the Ni(ii)-quinonoid complex, [Ni(HLMe)2] (H2LMe = 4-methylamino-6-methyliminio-3-oxocyclohexa-1,4-dien-1-olate), which was reported to exhibit vapochromic spin-state switching between high and low spin states, the chloranilato complex does not change its spin state even after the removal of coordinated vapour molecules. X-ray absorption fine structure (XAFS) analysis revealed that the six-coordinate geometry of {Ni(ca)(VM)2}n was maintained even after the removal of vapour molecules, in contrast to the [Ni(HLMe)2] complex. The unique vapochromism that follows the dimensional change between 1D and higher is influenced by the relatively weaker ligand field of the chloranilate ligand.

Transparent Ion-Exchange Membrane Exhibiting Intense Emission under a Specific pH Condition Based on Polypyridyl Ruthenium(II) Complex with Two Imidazophenanthroline Groups

The development and the photophysical behavior of a transparent ion-exchange membrane based on a pH-sensitive polypyridyl ruthenium(II) complex, [(bpy)2RuII(H2bpib)RuII(bpy)2](ClO4)4 (bpy = 2,2'-bipyridine, H2bpib = 1,4-bis([1,10]phenanthroline[5,6-d]-imidazol-2-yl)benzene), are experimentally and theoretically reported. The emission spectra of [(bpy)2RuII(H2bpib)RuII(bpy)2]@Nafion film were observed between pH 2 and pH 11 and showed the highest relative emission intensity at pH 5 (λmaxem = 594.4 nm). The relative emission intensity of the film significantly decreased down to 75% at pH 2 and 11 compared to that of pH 5. The quantum yields (Φ) and lifetimes (τ) showed similar correlations with respect to pH, Φ = 0.13 and τ = 1237 ns at pH 5, and Φ = 0.087 and τ = 1014 ns and Φ = 0.069 and τ = 954 ns at pH 2 and pH 11, respectively. These photophysical data are overall considerably superior to those of the solution, with the radiative- (kr) and non-radiative rate constants (knr) at pH 5 estimated to be kr = 1.06 × 105 s-1 and knr = 7.03 × 105 s-1. Density functional theory calculations suggested the contribution of ligand-to-ligand- and intraligand charge transfer to the imidazolium moiety in Ru-H3bpib species, implying that the positive charge on the H3bpib ligand works as a quencher. The Ru-Hbpib species seems to enhance non-radiative deactivation by reducing the energy of the upper-lying metal-centered excited state. These would be responsible for the pH-dependent "off-on-off" emission behavior.

Rapid preparation of a Nafion/Ag NW composite film and its humidity sensing effect

In this study, we present a novel humidity-responsive composite film based on the integration of two silver nanowire (Ag NW) layers deposited via the physical deposition process with an ionomer (Nafion) layer sandwiched between them. As a result of the ion migration inside the ionomer, the humidity to electrical transduction displays a fast response and high sensitivity in comparison with previous research. Meanwhile, the effects of the humidity gradient on the sensing response of the Nafion/Ag NWs composite film were investigated. Specifically, a higher humidity enables a faster response rate but a slower recovery rate, as compared to a lower humidity level. In addition, breathing tests are performed, which verified the opportunities for the design and fabrication of high-performance sensors for environment and biophysical monitoring. This research also revealed the potential applications in VOC (volatile organic compound) detection.

In this study, a novel electrical humidity-responsive composite film was presented based on the integration of two silver nanowire (Ag NW) layers deposited via the physical deposition process with a Nafion layer sandwiched between them.

Reversible solid-state thermochromism of a 2D organic–inorganic hybrid perovskite structure based on iodoplumbate and 2-aminomethyl-pyridine

An organic–inorganic hybrid solid [(PyCH₂NH₃)₆][Pb₅I₂₂]·3H₂O with a 2D inorganic layer exhibited a reversible color change from orange to red at 80 °C in the solid state.

Dehydration of Octacyanido-Bridged NiII-WIV Framework toward Negative Thermal Expansion and Magneto-Colorimetric Switching

An inorganic three-dimensional [Ni^II(H₂O)₂]₂[W^IV(CN)₈]·4H₂O (1) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase Ni^II₂[W^IV(CN)₈] (1d). The dehydration process induces changes in optical, magnetic, and thermal expansion properties. While 1 reveals typical positive thermal expansion of the crystal lattice, greenish-yellow color, and paramagnetic behavior, 1d is the first ever reported octacyanido-based solid revealing negative thermal expansion, also exhibiting a deep red color and diamagnetism. Such drastic shift in the physical properties is explained by the removal of water molecules, leaving the exclusively cyanido-bridged bimetallic network, which is accompanied by the transformation of the octahedral paramagnetic [Ni^II(H₂O)₂(NC)₄]^2- to the square-planar diamagnetic [Ni^II(NC)₄]^2- moieties.

Colorimetric Humidity and Solvent Recognition Based on a Cation-Exchange Clay Mineral Incorporating Nickel(II)-Chelate Complexes

Solvatochromic nickel(II) complexes with diketonato and diamine ligands were incorporated into a saponite clay by ion exchange, and their colorimetric humidity- and solvent-recognition properties were investigated. These powders exhibit color change from red to blue-green depending on humidity, and the detection range can be controlled by modifying the metal complex. The humidity response takes advantage of the humidity-dependent water content in clay and the coordination of water molecules to the metal complex in equilibrium. The addition of organic solvents to the powders causes a color change to occur, varying from red to blue-green depending on the donor number of the solvent, thereby enabling solvent recognition. In the clay, the affinity of less sterically hindered complexes to water or solvent molecules is decreased compared with that in solution because the cationic complexes interact with the anionic layers in the clay. Incorporating diethylene glycol into the materials produced thermochromic powders.

Silver nanoparticle based highly selective and sensitive solvatochromatic sensor for colorimetric detection of 1,4-dioxane in aqueous media

A silver nanoparticle based solvatochromic sensor that selectively and sensitively detects 1,4-dioxane in aqueous media has been developed. The nanoparticle surfaces generate ROS, which promote 1,4-dioxane degradation, causing a sharp colour change.