Magnetic and Electrochemical Properties of a TEMPO‐Substituted Disulfide Diradical in Solution,in the Crystal,and on a Surface

A study of the magnetic and electrochemical properties of a TEMPO‐substituted disulfide diradical in three different environments was carried out: in solution, in the crystal, and as a self‐assembled monolayer (SAM) on an Au(111) substrate, and the relationship between them was explored. In solution, this flexible diradical shows a strong spin‐exchange interaction between the two nitroxide functions that depends on the temperature and solvent. Structural, dynamic, and thermodynamic information has been extracted from the EPR spectra of this dinitroxide. The magnetic interactions in the crystal include intra‐ and intermolecular contributions, which have been studied separately and shown to be antiferromagnetic in both cases. Finally, we demonstrate that both the magnetic and electrochemical properties are preserved upon chemisorption of the diradical on a gold surface. The resulting SAM displayed anisotropic magnetic properties, and angle‐resolved EPR spectra of the monocrystal allowed a rough determination of the orientation of the molecules in the SAM.     

A new multifunctional ferrocenyl-substituted ferrocenophane derivative: optical and electronic properties and selective recognition of Mg2+ ions

The synthesis, characterisation, and X-ray structure of a new strained asymmetric diferrocene derivative (2) is reported. Compound 2 acts as a highly specific electrochemical and optical Mg(2+) ion sensor, as revealed by spectroscopic and electrochemical techniques. Thus, in the presence of Mg(2+), a new redox peak appears in the cyclic voltammogram (CV) that is anodically shifted compared to the E(1/2) of the free receptor (DeltaE(1/2)=340 mV). Diferrocene derivative 2 also gives a highly visual response upon addition of Mg(2+), namely a change of colour from orange to deep purple. In addition, compound 2 does not show any significant sensing activity in the presence of Ca(2+) or alkaline ions. On protonation, it is converted into the stable diferrocenylcarbenium salt 4, in which two different modes of stabilisation of the alpha-carbocationic centre are clearly demonstrated by a combination of (1)H NMR and (57)Fe M?ssbauer spectroscopic measurements. Finally, by a partial (chemical or electrochemical) oxidation, compound 2 forms the asymmetric mixed-valence species 2(+), which can be isolated as the solid salt 6 by using CF(3)SO(3) (-) as a counterion. This mixed-valence species shows a fast intramolecular electron-transfer process, as ascertained by several spectroscopic techniques.     

An unusually stable trinuclear manganese(II) complex bearing bulk carboxylic radical ligands

A trinuclear MnII cluster based on the versatile polychlorinated triphenylmethyl carboxylic radical ligand has been characterized by X-ray crystallography and magnetic measurements, representing a rare example of a MnII trinuclear linear structure with six open-shell ligands.     

A new valence tautomerism example in an electroactive ferrocene substituted triphenylmethyl radical

A new molecular system combining an open-shell organic radical that acts as an acceptor group, different from an o-quinone moiety, covalently linked to a ferrocene moiety, acting as the donor group, is shown to exhibit valence tautomerism.     

An Electrically Driven and Readable Molecular Monolayer Switch Based on a Solid Electrolyte

The potential application of molecular switches as active elements in information storage has been demonstrated through numerous works. Importantly, such switching capabilities have also been reported for self‐assembled monolayers (SAMs). SAMs of electroactive molecules have recently been exploited as electrochemical switches. Typically, the state of these switches could be read out through their optical and/or magnetic response. These output reading processes are difficult to integrate into devices, and furthermore, there is a need to use liquid environments for switching the redox‐active molecular systems. In this work, both of these challenges were overcome by using an ionic gel as the electrolyte medium, which led to an unprecedented solid‐state device based on a single molecular layer. Moreover, electrochemical impedance has been successfully exploited as the output of the system.     

Grafting of monocarboxylic substituted polychlorotriphenylmethyl radicals onto a COOH-functionalized self-assembled monolayer through copper (II) metal ions

A monocarboxylic substituted polychlorotriphenylmethyl radical (PTMCOOH) has been grafted onto a COOH-functionalized SAM (mercaptohexadecanoic acid, MHDA SAM), using copper (II) metal ions as linkers between the carboxyl groups of the SAM and the ligand. The metal-radical adlayer has been characterized thoroughly using different surface analysis techniques, such as contact angle, IRRAS, XPS, SPR, ToF-SIMS, SFM, and NEXAFS. The magnetic character was confirmed by EPR. The density of unoccupied states was investigated using X-ray absorption spectroscopy. A low-energy peak in the NEXAFS spectrum directly revealed the presence of partially occupied electronic levels, thus proving the open-shell character of the grafted ligands. SEM measurements on a laterally patterned sample prepared by muCP of MHDA in a matrix of hexadecane thiolate (a CH 3-terminated SAM) was performed to demonstrate that the metal-assisted anchoring of the open-shell ligand occurs selectively on the COOH terminated SAM. These results represent an easy and new approach to anchor organic radicals on surfaces and constitute a first step toward the growth of magnetic metal-organic radical-based frameworks on solid substrates.     

Self-assembled monolayers of electroactive polychlorotriphenylmethyl radicals on Au(111)

Two new polychlorotriphenylmethyl (PTM) derivatives bearing a thioacetate and a disulfide group have been synthesized to anchor on gold substrate. On the basis of these molecules, three strategies were followed to prepare self-assembled monolayers (SAMs) of electroactive PTMs. The resulting SAMs were fully characterized by contact angle, atomic force microscopy (AFM), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The high coverage surface and stability of the SAMs were demonstrated by cyclic voltammetry. In addition, the electrochemical experiments proved that these SAMs are bistable since it is possible to reversibly switch between the PTM radical state to the corresponding anion. The magnetic response was investigated by electron paramagnetic resonance. We observed that when the PTM SAMs are in their radical form they confer magnetic functionality to the surface, whereas when they are in the anionic state, the surface is diamagnetic. Thus, the PTM-modified substrates are multifunctional surfaces since they combine magnetic and electroactive properties. The reported results show the high potential of these materials for the fabrication of surface molecular devices.     

Highly selective chromogenic and redox or fluorescent sensors of Hg2+ in aqueous environment based on 1,4-disubstituted azines

Two new chemosensors that exhibit high affinity and high selectivity for Hg2+ in aqueous environment which operate through two different channels, optic/redox and optic/fluorescent, are reported. The optical change in sensing can be used even for a "naked-eye" detection of Hg2+ ions, whereas the fluorescent response can be modulated by varying the solvent polarity.