Triggering Two-Step Spin Bistability and Large Hysteresis in Spin Crossover Nanoparticles via Molecular Nanoengineering

The local entrapment of the spin crossover complex Fe­(II)-tris­[2-(2′-pyridyl)­benzimidazole] into the pluronic polymeric matrix (P123, PEG20–PPG70–PEG20, MW ∼ 5800) yielded the formation of magnetic nanoparticles of ∼26 nm (SCO-Np). Formation of SCO-Np was driven by the emergence of noncovalent interactions between the aromatic −NH group of the benzimidazole moieties present in Fe­(II)-tris­[2-(2′-pyridyl)­benzimidazole] with the aliphatic ether (−O−) groups of the pluronic polymeric matrix. The nanoparticles show spin crossover behavior, two-step spin bistability, and wide magnetic hysteresis, expressed in the temperature range of 170–280 K (Δ<i>T</i>_max = 38 K). The neat SCO molecules, Fe­(II)-tris­[2-(2′-pyridyl)­benzimidazole], on the contrary show only first-order spin transition and negligible hysteresis. The developed matrix-confinement approach of SCO molecules shown in this work yielded an unprecedented and significant improvement of the magnetic cooperativity compared to the neat spin crossover system, despite the decreased dimension of the magnetic domain in the nanosized architecture

Anodic Oxidation of 18 Halogenated and/or Methylated Derivatives of CB₁₁H₁₂^–

Anodic oxidation of [CB₁₁H₁₂]⁻ and 18 of its halogenated and/or methylated derivatives was examined. Reversible oxidation was found for four of the anions in liquid SO₂ and for four more in 1,1,1,3,3,3-hexafluoroisopropyl alcohol. The oxidation occurred at ∼1 V (for [CB₁₁Me₁₂]⁻) up to more than 4 V (for [1-H-(2–6)-F₅-(7–12)-(CF₃)₆-CB₁₁]⁻) relative to ferrocene/ferricinium. The anodic peak potentials are reproduced by a set of additive position-sensitive substituent increments

Hydrogenated Fluorographene: A 2D Counterpart of Graphane with Enhanced Nonlinear Optical Properties

We describe the benign wet chemical synthesis, characterization, and third-order nonlinear optical properties of hydrogenated fluorographene, namely, of a new 2D counterpart of hydrogenated graphene (graphane). The presence of hydrogen in hydrogenated fluorographene was confirmed using infrared spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis coupled with evolved gas analysis. The nonlinear optical properties of the derivative were investigated in the visible and infrared using picosecond laser excitation and were compared to those of graphene and fluorographene. All samples were found to exhibit important nonlinear optical response, with hydrogenated fluorographene exhibiting the largest response under visible excitation (ca. 1 order of magnitude higher compared to graphene and fluorographene). This is among the highest recorded effects ever observed for any graphene-based materials, including graphene oxide presented elsewhere. The results reveal the importance of the nature of the functional group and the degree of functionalization (i.e., fluorination and hydrogenation) on the nonlinear optical properties of graphenes. It is likely that highly polarized donor-π electron-acceptor regions within a layer result in such large optical nonlinearities

Functional Nanosheet Synthons by Covalent Modification of Transition-Metal Dichalcogenides

We report on the facile preparation of versatile MoS₂–thiobarbituric acid conjugates, which, in addition to excellent electrochemical behavior, can serve as nanosheet platforms for further functionalization in a multitude of applications. We show that chemically exfoliated MoS₂ was extensively modified with up to 50% surface coverage, while maintaining its metallic character, and that the strategy can be extended to MoSe₂, WS₂, and WSe₂. The covalent functionalization endowed the materials not only with good aqueous dispersibility, but also with improved hydrogen evolution reaction (HER) activity, as well as promise in the oxidative detection of DNA nucleobases in solution