Hysteresis Photomodulation within photochromic assemblies of [Dy(Tp2-py)F]+ Single-Molecule Magnets : Influence of the supramolecular magnetic couplings.

A 1D coordination compound made of a photochromic dithienylethene linker and [Dy(Tp2-py)F]+ units (with Tp2-py = tris(3-(2-pyridyl)pyrazolyl)hydroborate) and having tetrakis[3,5-bis(trifluoromethyl)phenyl]borate counterions is reported. Full photoconversion from the closed isomer to the open isomer of the dithienyethene within single crystals allow for monitoring of the transformation by photocrystallography. Magnetic slow relaxation as well as magnetic hysteresis are observed and can be both modulated upon light irradiation.

A novel combinatorial approach integrating experimental and computational analysis of antioxidant activity: Evaluating catechin and L-ascorbic acid in serum.

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality globally, with oxidative stress playing a pivotal role in its progression. Free radicals produced via oxidative stress contribute to lipid peroxidation, leading to subsequent inflammatory responses, which then result in atherosclerosis. Antioxidants inhibit these harmful effects through their reducing ability, thereby preventing oxidative damage.

The Many Facets of Ru(dppe) Acetylide Compounds.

In this contribution, we describe the various research domains in which Ru alkynyl derivatives are involved. Their peculiar molecular properties stem from a strong and intimate overlap between the metal centered d orbitals and the π system of the acetylide ligands, resulting in plethora of fascinating properties such as strong and tunable visible light absorption with a strong MLCT character essential for sensing, photovoltaics, light-harvesting applications or non-linear optical properties. Likewise, the d/π mixing results in tunable redox properties at low potential due to the raising of the HOMO level, and making those compounds particularly suited to achieve redox switching of various properties associated to the acetylide conjugated ligand, such as photochromism, luminescence or magnetism, for charge transport at the molecular level and in field effect transistor devices, or charge storage for memory devices.

Kinetic Delay in Cooperative Supramolecular Polymerization by Redefining the Trade-Off Relationship between H-Bonds and Van der Waals/π-π Stacking Interactions.

We here present how rebalancing the interplay between H-bonds and dispersive forces (Van der Waals/π-π stacking) may induce or not the generation of kinetic metastable states. In particular, we show that extending the aromatic content and favouring the interchain VdW interactions causes a delay into the cooperative supramolecular polymerization of a new family of toluene bis-amide derivatives by trapping the metastable inactive state.

A photochromic metallacycle with highly anisotropic Dy-F magnetic units.

A dinuclear metallacycle assembled from a bispyridyl dithienylethene linker and a highly anisotropic dysprosium based Single Molecule Magnet (SMM) shows magnetic hysteresis at 1.8 K together with photoisomerization in single crystals (SC). The impact of photoswitching on the SMM behavior is evidenced and related to the specific organization of the magnetic units.

Ytterbium(III) Complex with Photochromic Ruthenium(II) Acetylide Ligand: All Visible Light Photoswitching of NIR Luminescence.

We report a ruthenium(II) bisacetylide complex bearing a photochromic dithienylethene (DTE) acetylide arm and a coordinating bipyridyl on the acetylide unit. Its coordination with Yb(TTA) centers (TTA = 2-thenoyltrifluoroacetonate) produces a bimetallic complex in which the dithienylethene isomerization is triggered by both ultraviolet (UV) light absorbed by the DTE unit and 450 nm excitation in a transition of the organometallic moiety. The redox behavior arising from the ruthenium(II) bisacetylide system is fully investigated by cyclic voltammetry and spectroelectrochemistry, revealing a lack of stability of the DTE-closed oxidized state preventing effective redox luminescence switching.

Electronic transport through single-molecule oligophenyl-diethynyl junctions with direct gold-carbon bonds formed at low temperature.

We report on the first systematic transport study of alkynyl-ended oligophenyl-diethynyl (OPA) single-molecule junctions with direct Au-C anchoring scheme at low temperature using the mechanically controlled break junction technique. Through quantitative statistical analysis of opening traces, conductance histograms and density functional theory studies, we identified different types of junctions, classified by their conductance and stretching behavior, for OPA molecules between Au electrodes with two to four phenyl rings. We performed inelastic electron tunneling spectroscopy and observed the excitation of Au-C vibrational modes confirming the existence of Au-C bonds at low temperature and compared the stability of molecule junctions upon mechanical stretching.

Dual-gated single-molecule field-effect transistors beyond Moore's law.

As conventional silicon-based transistors are fast approaching the physical limit, it is essential to seek alternative candidates, which should be compatible with or even replace microelectronics in the future. Here, we report a robust solid-state single-molecule field-effect transistor architecture using graphene source/drain electrodes and a metal back-gate electrode. The transistor is constructed by a single dinuclear ruthenium-diarylethene (Ru-DAE) complex, acting as the conducting channel, connecting covalently with nanogapped graphene electrodes, providing field-effect behaviors with a maximum on/off ratio exceeding three orders of magnitude.

Tunable Symmetry-Breaking-Induced Dual Functions in Stable and Photoswitched Single-Molecule Junctions.

The aim of molecular electronics is to miniaturize active electronic devices and ultimately construct single-molecule nanocircuits using molecules with diverse structures featuring various functions, which is extremely challenging. Here, we realize a gate-controlled rectifying function (the on/off ratio reaches ∼60) and a high-performance field effect (maximum on/off ratio >100) simultaneously in an initially symmetric single-molecule photoswitch comprising a dinuclear ruthenium-diarylethene (Ru-DAE) complex sandwiched covalently between graphene electrodes. Both experimental and theoretical results consistently demonstrate that the initially degenerated frontier molecular orbitals localized at each Ru fragment in the open-ring Ru-DAE molecule can be tuned separately and shift asymmetrically under gate electric fields.

Metal complexes bearing photochromic ligands: photocontrol of functions and processes.

Metal complexes associated with photochromic molecules are attractive platforms to achieve smart light-switching materials with innovative and exciting properties due to specific optical, electronic, magnetic or catalytic features of metal complexes and by perturbing the excited-state properties of both components to generate new reactivity and photochemical properties. In this overview, we focus on selected achievements in key domains dealing with optical, redox, magnetic properties, as well as application in catalysis or supramolecular chemistry. We also try to point out scientific challenges that are still faced for future developments and applications.

Quantifying Image Charge Effects in Molecular Tunnel Junctions Based on Self-Assembled Monolayers of Substituted Oligophenylene Ethynylene Dithiols.

A number of factors contribute to orbital energy alignment with respect to the Fermi level in molecular tunnel junctions. Here, we report a combined experimental and theoretical effort to quantify the effect of metal image potentials on the highest occupied molecular orbital to Fermi level offset, ε, for molecular junctions based on self-assembled monolayers (SAMs) of oligophenylene ethynylene dithiols (OPX) on Au. Our experimental approach involves the use of both transport and photoelectron spectroscopy to extract the offsets, ε and ε, respectively.

Molecular Engineering onto Ru Bis(1,2-diphenylphosphinoethane) Synthon: Toward an Original Organometallic Gelator.

In this article, we report the successful molecular engineering of Ru bis-acetylides that led for the first time to a gelator and more specifically in aromatic solvents. By means of a nonlinear ligand and an extended aromatic platform, the bulky Ru bis-acetylides were able to self-assemble into lamellar structures as evidenced by scanning electron microscopy (SEM) in benzene, toluene, and - and -xylene, which in turn induced gelation of the solution with a critical gelation concentration of 30 mg/mL. Nuclear magnetic resonance (NMR), variable temperature (VT)-NMR, and Fourier transform infrared (FT-IR) spectroscopies evidenced that hydrogen bonds are mainly responsible for the self-organization.

Hysteresis Photomodulation via Single-Crystal-to-Single-Crystal Isomerization of a Photochromic Chain of Dysprosium Single-Molecule Magnets.

A one-dimensional coordination solid is synthesized by reaction of a bispyridyl dithienylethene (DTE) photochromic unit with the highly anisotropic dysprosium-based single-molecule magnet [Dy(Tp)F(pyridine)]PF. Slow magnetic relaxation characteristics are retained in the chain compound , and photoisomerization of the bridging DTE ligand induces a single-crystal-to-single-crystal transformation that can be monitored using photocrystallography. Notably, the resulting chain compound exhibits faster low-temperature relaxation than that of , which is apparent in magnetic hysteresis data collected for both compounds as high as 4 K.

Dual Light and Redox Control of NIR Luminescence with Complementary Photochromic and Organometallic Antennae.

With the help of a judicious association between dithienylethene (DTE) units, an ytterbium ion, and a ruthenium carbon-rich complex, we describe (i) the efficient (on/off) switching of pure NIR luminescence with a photochromic unit absorbing in the UV range and (ii) the association of electrochemical and photochemical control of this NIR emission in a single system with nondestructive readout.

Self-Assembled Monolayers of Redox-Active 4d-4f Heterobimetallic Complexes.

In this work, we report the preparation of functional interfaces incorporating heterobimetallic systems consisting in the association of an electroactive carbon-rich ruthenium organometallic unit and a luminescent lanthanide ion (Ln = Eu and Yb). The organometallic systems are functionalized with a terminal hexylthiol group for subsequent gold surface modification. The formation of self-assembled monolayers (SAMs) with these complex molecular architectures are thoroughly demonstrated by employing a combination of different techniques, including infrared reflection absorption spectroscopy, ellipsometry, contact angle, and cyclic voltammetry measurements.

Redox-driven porphyrin based systems for new luminescent molecular switches.

In this work, we explore the possibility of tuning the fluorescence intensity of two porphyrin systems through the electrochemical oxidation of an appended ruthenium acetylide bridge. Two electrochemically switchable systems, a dyad (ZnP-Ru, 3) and a triad (ZnP-Ru-P2H, 5), were prepared and investigated. In the ZnP-Ru dyad, the fluorescence of the zinc porphyrin was switched reversibly between the ON and OFF state upon the oxidation of the ruthenium unit, the most probable quenching process involved after oxidation being the electron transfer from the singlet excited state of ZnP to the oxidized ruthenium center.

HOMO Level Pinning in Molecular Junctions: Joint Theoretical and Experimental Evidence.

A central issue in molecular electronics in order to build functional devices is to assess whether changes in the electronic structure of isolated compounds by chemical derivatization are retained once the molecules are inserted into molecular junctions. Recent theoretical studies have suggested that this is not always the case due to the occurrence of pinning effects making the alignment of the transporting levels insensitive to the changes in the electronic structure of the isolated systems. We explore here this phenomenon by investigating at both the experimental and theoretical levels the I/ V characteristics of molecular junctions incorporating three different three-ring phenylene ethynylene derivatives designed to exhibit a significant variation of the HOMO level in the isolated state.

trans to cis photo-isomerization in merocyanine dysprosium and yttrium complexes.

We report the synthesis of two lanthanide complexes including a chelating merocyanine (MC) ligand obtained from the reaction of a bis(pyridinemethyl)amine substituted spiropyran with yttrium(iii) or dysprosium(iii) triflate salts, whose structures were confirmed both in the solid state and in solution by single crystal X-ray diffraction studies and NMR investigations. The obtained merocyanine metal complexes can reversibly undergo a photo-triggered transformation consisting of a partial isomerization of the trans-merocyanine ligand to its cis isomer (cis-MC) providing complexes in which the metal-phenolate bond is retained. SQUID magnetometry experiments in combination with ab initio calculations were used to evidence and rationalize the single-molecule magnet behavior of the dysprosium complex and to probe the changes in the dysprosium ion local environment upon photo-isomerization.

A Terminal Fluoride Ligand Generates Axial Magnetic Anisotropy in Dysprosium Complexes.

The first dysprosium complexes with a terminal fluoride ligand are obtained as air-stable compounds. The strong, highly electrostatic dysprosium-fluoride bond generates a large axial crystal-field splitting of the J=15/2 ground state, as evidenced by high-resolution luminescence spectroscopy and correlated with the single-molecule magnet behavior through experimental magnetic susceptibility data and ab initio calculations.

Ruthenium Carbon-Rich Group as a Redox-Switchable Metal Coupling Unit in Linear Trinuclear Complexes.

The preparation and properties of novel ruthenium carbon-rich complexes [(Ph-C≡C-)Ru(dppe)(-C≡C-bipyM(hfac))] (n = 1, 2; M = Cu, Mn; bipy = 2,2'-bipyridin-5-yl) characterized by single-crystal X-ray diffraction and designed for molecular magnetism are reported. With the help of EPR spectroscopy, we show that the neutral ruthenium system sets up a magnetic coupling between two remote paramagnetic Cu units. More specifically, these copper compounds are unique examples of bimetallic and linear heterotrimetallic compounds for which a complete rationalization of the magnetic interactions could be made for exceptionally long distances between the spin carriers (8.

Dual-Responsive Molecular Switches Based on Dithienylethene-Ru Organometallics in Self-Assembled Monolayers Operating at Low Voltage.

Two carbon-rich ruthenium complexes bearing a dithienylethene (DTE) unit and a hexylthiol spacer were designed to be attached on gold surfaces. Both compounds display photochemically driven switching properties, allowing reversible conversion from open to closed forms of the DTE units upon irradiation in solution. In contrast, only the bimetallic complex undergoes an efficient electrochemical ring closure at low potential, (0.

Modulation of Eu(III) and Yb(III) Luminescence Using a DTE Photochromic Ligand.

In this work, we show that a dithienylethene (DTE) modified dipicolinic amide ligand can be a versatile tool to modulate Eu(III) and Yb(III) luminescence using light as an external stimulus. The nature of the modulation depends on the lanthanide emitter: with the europium ion, the DTE ligand quenches the red luminescence upon ring closure, whereas with the ytterbium ion, ring closure can be used to turn on the luminescence in the NIR range.

Highly Axial Magnetic Anisotropy in a N O Dysprosium(III) Coordination Environment Generated by a Merocyanine Ligand.

A spiropyran-based switchable ligand isomerizes upon reaction with lanthanide(III) precursors to generate complexes with an unusual N O coordination sphere. The air-stable dysprosium(III) complex shows a hysteresis loop at 2 K and a very strong axial magnetic anisotropy generated by the merocyanine phenolate donor.

NIR Electrofluorochromic Properties of Aza-Boron-dipyrromethene Dyes.

The photophysical properties of near-infrared (NIR) emissive aza-boron-dipyrromethene (aza-BDP) dyes incorporating nitrofluorene and alkoxy decorations were intensively investigated. Their highly reversible one-electron reduction process showed characteristic electrofluorochromic (EF) properties in the NIR range, depending on the substituents. The nitrofluorene ethynyl-substituted (Type I) dyes showed smaller EF effects than the alkoxy-containing (Type II) dyes because of the difference in their intrinsic fluorescence contrast between the neutral and reduced states (radical anion).

Ruthenium Carbon-Rich Complexes as Redox Switchable Metal Coupling Units.

With the help of EPR spectroscopy, we show that the diamagnetic [Ru(dppe)2(-C≡C-R)2] system sets up a magnetic coupling between two organic radicals R, i.e., two nitronyl nitroxide or two verdazyl units, which is stronger than that of related platinum organometallic systems.