Ethylenedithio--Tetrathiafulvalene--Helicenes: Electroactive Helical Precursors with Switchable Chiroptical Properties

International audienceElectroactive fused ethylenedithio-tetrathiafulvalene-[4]helicene and -[6]helicenes have been synthesized through a strategy involving the preparation of 2,3-dibromo-helicene derivatives as intermediates. The dihedral angles between the terminal helicenes, as determined by single crystal X-ray analyses, amount to 22.7° and 50.7° for the [4]helicene and [6]helicene, respectively. The solid state architectures show interplay between S···S and ··· intermolecular interactions. The chiroptical properties of the enantiopure EDT-TTF-[6]helicene derivatives have been investigated and supported by TD DFT calculations. Remarkable redox switching of the circular dichroism signal between the neutral and radical cation species has been achieved

Lanthanide-Based Metal–Organic Frameworks with Single-Molecule Magnet Properties

Lanthanide metal-organic frameworks (Ln-MOFs) showing single-molecule magnet (SMM) properties are an ever-growing family of materials where the magnetic properties can be tuned by various interrelated parameters, such as the coordinated solvent, temperature, organic linkers, lanthanide ions and their coordination environment. An overview of the general synthetic methodologies to access MOFs/Ln-MOFs and the peculiarities and parameters to control and/or fine-tune their SMM behavior is herein presented. Additionally, diverse challenging strategies for inducing SMM/SIM behavior in an Ln-MOF are discussed, involving redox activity and chirality. Furthermore, intriguing physical phenomena such as the CISS effect and CPL are also highlighted

Syntheses, Structures, and Photophysical Properties of Mono- and Dinuclear Sulfur-Rich Gold(I) Complexes

Sulfur-rich 1,2 dithiolene and neutral thione ligands were used for the synthesis of gold complexes, some of them exhibiting aurophilic interactions. Surprisingly, the closest Au···Au contact is observed in an unsupported dinuclear complex, which makes part of a supramolecular network. Photophysical studies, combined with DFT calculations, indicate that the participations of the Au···Au interactions have some relevance to the rich luminescence properties of these compounds

Stereospecific on-Surface Cyclodehydrogenation of Bishelicenes: Preservation of Handedness from Helical to Planar Chirality

Flattening helices while keeping the handedness: On-surface cyclodehydrogenation of bishelicene enantiomers leads stereospecifically to (M,M) and (P,P) chiral planar polyaromatic hydrocarbons. This is followed by their homochiral aggregation into a 2D conglomerate. Thermally induced cyclodehydrogenation proceeds stereospecifically to chiral, planar coronocoronene. Such a reaction is a special example of topochemistry in which enantiospecific conversion is supported by the alignment of the reactant by the surface

Highly Stereospecific On‐Surface Dimerization into Bishelicenes: Topochemical Ullmann Coupling of Bromohelicene on Au(111)

The on‐surface dimerization into bis(hexahelicene) on a gold(111) surface has been studied by means of scanning tunneling microscopy and time‐of‐flight secondary mass spectrometry. C−C Ullmann coupling of (rac)‐2‐bromo‐hexahelicene leads to formation of the (M,M)‐ and (P,P)‐diastereomers of 2,2’‐bis(hexahelicene), whilst formation of the (M,P)‐diastereomer is not observed. Upon cooling, the bis(hexahelicene) aggregates into an ordered two‐dimensional lattice with partly randomly distributed enantiomers. The highly specific diastereomeric coupling is explained by the surface alignment of educt in combination with the strong steric overcrowding in a possible surface‐confined (M,P)‐product

A Highly Conducting Tetrathiafulvalene-Tetracarboxylate Based Dysprosium(III) 2D Metal-Organic Framework with Single Molecule Magnet Behaviour

The synthesis and whole characterization by a multitechnique approach of an unprecedented dysprosium(iii) 2D metal organic framework (MOF), involving the redox-active tetrathiafulvalene (TTF)-based linker TTF-tetracarboxylate (TTF-TC), are herein reported. The single-crystal X-ray structure, formulated as [Dy6(TTF-TC)5(H2O)22]·21H2O (1), reveals a complex 2D topology, with hexanuclear Dy6 clusters as secondary building units (SBUs) interconnected by five linkers, stacked almost parallel in each layer and eclipsed along the [111] direction, leading to the formation of 1D channels filled by water molecules. The mixed valence of the TTF units is confirmed by both bond distance analysis, Raman microscopy and diffuse reflectance spectroscopy, and further supported by band structure calculations, which also predict activated conductivity for this material. Thanks to efficient TTF stacking and partial oxidation, 1 shows semiconducting behavior, with, however, a record conductivity value of 1 mS cm−1 at room temperature, when compared to the previously reported TTF-based MOFs. Furthermore, temperature and magnetic field dependent ac (alternative current) magnetic susceptibility measurements demonstrate field induced slow relaxation of magnetization, accounting for two independent relaxation processes, with an energy barrier (Ueff/K) of around 12 K, typical for dysprosium carboxylate complexes. The herein reported 2D Dy-MOF provides a valuable master plan for coexistence of conducting π-TTF stacks and highly anisotropic DyIII SMM properties

Thiophenyl Anilato-Based NIR-Emitting Lanthanide (LnIII = Er, Yb) Dinuclear Complexes

By combining ErIII and YbIII ions with 3,6-dithiophene-anilate (Th2An) and scorpionate hydrotris(pyrazol-1-yl)borate (HBpz3−) ligands new luminescent dinuclear complexes are obtained. The two materials formulated as [((HB(pz)3)2Yb)2(μ-th2An)]·4DCM·1.3H2O 1Yb and [((HB(pz)3)2Er)2(μ-th2An)]·4DCM·1.8H2O 1Er, respectively, have been structurally characterized by SC-XRD and PXRD studies. This study presents a comprehensive investigation of the photophysical properties of the Th2An ligand for the first time. Our findings reveal the crucial role of the thiophene anilate as an effective optical antenna, which sensitizes near-infrared (NIR)-emitting lanthanide ions, specifically ErIII and YbIII. The significant impact of vibrational quenching on the LnIII NIR emission efficiency has been also highlighted

In Search of Chiral Molecular Superconductors: κ-[(S,S)-DM-BEDT-TTF]2ClO4 Revisited

The relationship between chirality and superconductivity is an intriguing question. The two enantiomeric crystalline radical cation salts κ-[(S,S)-DM-BEDT-TTF]2ClO4 and κ-[(R,R)-DM-BEDT-TTF]2ClO4, showing κ-type arrangement of the organic layers, are investigated in search for superconducting chiral molecular materials following a 1992 report indicating the occurrence of a superconducting transition in the former compound. While the initial interpretation is presently challenged through in-depth temperature and pressure dependent single crystal resistivity measurements combined with band structure calculations, the two chiral conductors show metal like behavior with room temperature conductivities of 10-30 S cm−1 at ambient pressure and stabilization of the metallic state down to the lowest temperatures under moderate pressures. Moreover, their structural and theoretical investigations reveal an original feature, namely the existence of two different κ layers with 1D and 2D electronic dimensionality, respectively, as a consequence of an interlayer charge transfer. The resistivity drop observed for one sample below 1 K and insensitive to magnetic field, possibly results from mixing in-plane and out-of-plane contributions to the measured resistance and suggests current induced charge order melting. This feature contradicts the occurrence of superconductivity in these chiral molecular conductors and leaves open the discovery of the first chiral molecular superconductors

Hybrid mesoporous electrodes evidence CISS effect on water oxidation

Controlling product selectivity is essential for improving the efficiency of multi-product reactions. Electrochemical water oxidation is a reaction of main importance in different applications, e.g., renewable energy schemes and environmental protection, where H2O2 and O2 are the two principal products. In this Communication, the product selectivity of electrochemical water oxidation was controlled by making use of the chiral induced spin selectivity (CISS) effect at mesoporous-TiO2 on the molecule-modified Au substrate. Our results show a decrease in H2O2 formation when using chiral hetero-helicene molecules adsorbed on the Au substrate. We propose a mechanism for this kinetic effect based on the onset of CISS-induced spin polarization on the Au-helicene chiral interface. We also present a new tunable substrate to investigate the CISS mechanism.Fil: Vensaus, Priscila. Universidad Nacional de San Martin. Instituto de Nanosistemas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Liang, Yuehwei. Ecole Polytechnique Federale de Lausanne. Max Planck-epfl Center For Molecularnanosciencie And Technology; FranciaFil: Zigon, Nicolas. Ecole Polytechnique Federale de Lausanne; FranciaFil: Avarvari, Narcis. Ecole Polytechnique Federale de Lausanne; FranciaFil: Mujica, Vladimiro. Centre National de la Recherche Scientifique; FranciaFil: Soler Illia, Galo Juan de Avila Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martin. Instituto de Nanosistemas; ArgentinaFil: Lingenfelder, Magalí Alejandra. Ecole Polytechnique Federale de Lausanne. Max Planck-epfl Center For Molecularnanosciencie And Technology; Franci

Combining chirality and hydrogen bonding in methylated ethylenedithio- tetrathiafulvalene primary diamide precursors and radical cation salts

Methyl- and dimethyl-ethylenedithio-tetrathiafulvalene ortho-diamide donors Me-EDT-TTF(CONH2)2 (1a) and DM-EDT- TTF(CONH2)2 (1b) have been prepared by the direct reaction of the corresponding diester precursors with aqueous ammonia solutions. The neutral (rac)-1a, (R)-1a, and (S,S)-1b donors have been characterized by single crystal X-ray diffraction. In the three compounds, which crystallized in the non-centrosymmetric monoclinic space group P21, the amide groups are disordered, yet they form the classical intra-molecular hydrogen bond for such an ortho-diamide motif. Electro- crystallization experiments afforded the mixed valence radical cation salts[(S,S)-1b]2XO4 and [(R,R)-1b]2XO4 (X = Cl, Re) containing four independent donors in the asymmetric unit, with the positive charge localized essentially on two donors, while the two others are neutral. The topology of the organic layer is of β′-type. Single crystal resistivity measurements show semiconducting behavior for [(S,S)-1b]2ClO4 and [(R,R)-1b]2ReO4, with a room temperature conductivity of 5 × 10−5 S cm−1 and activation energies Ea ≈ 3000 K. Tight-binding band structure calculations of extended Hückel type in combination with density functional theory calculations are in agreement with the semiconducting behavior and suggest a localized Mott type semiconductor rather than a band gap semiconductor