Rational design of a material for rapid colorimetric Fe2+ detection

We report on the rational design of a novel TiO2 based screen-printed material suitable for sensitive and selective detection of iron ions in water. This includes the synthesis and characterization of large mesoporous TiO2 nanostructures, screen-printing of thick titania films on glass surfaces and their functionalization with 2,2':6',2″-terpyridin-4'-ylphosphonic acid (terpy). The ultra-high affinity between iron ions and the TiO2-anchored terpy receptor makes this system potentially applicable to the analysis of iron in environmental, food, biological, and biomedical systems by a readily quantifiable colour change. Rapid (<30 s) colour change of the material from white to magenta permits easy detection of as low as 0.3 ppm of Fe2+ by the naked eye. The intensity of the colour change depends on the nature of the nanoparticles, the overall TiO2 film thickness, and the Fe2+ concentration. The material was characterized using profilometry, diffuse reflectance UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) before and after treatment with aqueous solutions of Fe2+. The designed material shows colour reversibility upon treatment with EDTA solutions, which allows for multiple reuses of the same film with no effect on sensitivity

Layer-by-Layer Assemblies of Coordinative Surface-Confined Electroactive Multilayers: Zigzag vs Orthogonal Molecular Wires with Linear vs Molecular Sponge Type of Growth

Surface-anchored coordination-based molecular assemblies (CBMA) are very powerful tools for the design of modern materials. The CBMAs were created using bis-terpyridine–iron coordination chemistry by the alternation of linear or bent bis-terpyridine ligands and Fe­(II) metal centers. The coordination of the bent ligand results in the formation of zigzag structures that experience linear growth with each successive deposition step. Interestingly, the deposition of the linear ligand has two distinct steps. During the first four deposition cycles, the thickness and iron uptake (surface coverage) of the multilayer change similarly to ones of the bent ligand based multilayer. However, during the following deposition cycles, the linear ligand based multilayer demonstrates significantly higher growth rate. This unusual behavior might be attributed with the reorganizational transformations leading to a higher organizational level of the assembly. As a result, a part of templating layer molecules, which due to sterical reasons cannot seed a molecular wire growth, and successfully formed molecular wires begin acting as by-holders or molecular sponges able to trap extra metal ions and provide these ions to the system during the next deposition step, thus speeding up the growth of the molecular wires. Indeed, incubation of linear assemblies in solutions of Zn­(II) or Cd­(II) demonstrates significant trapping abilities for the ions. During electrochemical cycling, both assemblies show high stability, fast response times, and sufficient coloration efficiencies that make them valuable building blocks for the design of novel electrochromic materials

Terpyridine-Based Monolayer Electrochromic Materials

Novel electrochromic (EC) materials were developed and formed by a two-step chemical deposition process. First, a self-assembled monolayer (SAM) of 2,2′:6′,2″-terpyridin-4′-ylphosphonic acid, L, was deposited on the surface of a nanostructured conductive indium–tin oxide (ITO) screen-printed support by simple submerging of the support into an aqueous solution of L. Further reaction of the SAM with Fe or Ru ions results in the formation of a monolayer of the redox-active metal complex covalently bound to the ITO support (Fe–L/ITO and Ru–L/ITO, respectively). These novel light-reflective EC materials demonstrate a high color difference, significant durability, and fast switching speed. The Fe-based material shows an excellent change of optical density and coloration efficiency. The results of thermogravimetric analysis suggest high thermal stability of the materials. Indeed, the EC characteristics do not change significantly after heating of Fe–L/ITO at 100 °C for 1 week, confirming the excellent stability and high EC reversibility. The proposed fabrication approach that utilizes interparticle porosity of the support and requires as low as a monolayer of EC active molecule benefits from the significant molecular economy when compared with traditional polymer-based EC devices and is significantly less time-consuming than layer-by-layer growth of coordination-based molecular assemblies