Bis(terpyridine) metal complex wires: Excellent long-range electron transfer ability and controllable intrawire redox conduction on silicon electrode

Design, Synthesis, and Characterization of Organometallic BODIPY-Ru(II) Dyads: Redox and Photophysical Properties with Singlet Oxygen Generation Capability†

A series of Ru(II)-acetylide complexes (Ru1, Ru2, and Ru1m) with alkynyl-functionalized borondipyrromethene (BODIPY) conjugates were designed by varying the position of the linker that connects the BODIPY unit to the Ru(II) metal center through acetylide linkage at either the 2-(Ru1) and 2,6-(Ru2) or the meso-phenyl (Ru1m) position of the BODIPY scaffold. The Ru(II) organometallic complexes were characterized by various spectroscopic methods, including nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, CHN, and high-resolution mass spectrometry (HRMS) analyses. The Ru(II)-BODIPY conjugates exhibit fascinating electrochemical and photophysical properties. All BODIPY-Ru(II) complexes exhibit strong absorption (εmax = 29,000-72,000 M-1 cm-1) in the visible region (λmax = 502-709 nm). Fluorescence is almost quenched for Ru1 and Ru2, whereas Ru1m shows the residual fluorescence of the corresponding BODIPY core at 517 nm. The application of the BODIPY-Ru(II) dyads as nonporphyrin-based triplet photosensitizers was explored by a method involving the singlet oxygen (1O2)-mediated photo-oxidation of diphenylisobenzofuran. Effective π-conjugation between the BODIPY chromophore and Ru(II) center in the case of Ru1 and Ru2 was found to be necessary to improve intersystem crossing (ISC) and hence the 1O2-sensitizing ability. In addition, electrochemical studies indicate electronic interplay between the metal center and the redox-active BODIPY in the BODIPY-Ru(II) dyads.

Crystalline Unipolymer Monolayer with High Modulus and Conductivity

The synthesis of crystalline polymer with a well-defined orientated state and a two-dimensional crystalline size beyond a micrometer will be essential to achieve the highest physical feature of polymer material but remain challenging. Herein, we show the synthesis of the crystalline unipolymer monolayer with an unusual ultrahigh modulus that is higher than the ITO substrate and high conductance by simultaneous electrosynthesis and manipulation. We find that the polymer monolayer has fully extended in the vertical and unidirectional orientation, which is proposed to approach their theoretically highest density, modulus, and conductivity among all aggregation formations of the current polymer. The modulus and current density can reach 40 and 1000 times higher than their amorphous counterpart. It is also found that these monolayers exhibit the bias- and length-dependent multiple charge states and asymmetrically negative differential resistance (NDR) effect, indicating that this unique molecular tailoring and ordering design is promising for multilevel resistive memory devices. Our work demonstrates the creation of a crystalline polymer monolayer for approaching the physical limit of polymer electronic materials and also provides an opportunity to challenge the synthetically iterative limit of an isolated ultra-long polymer.

Chemically Laminated 2D Bis(terpyridine)metal Polymer Films: Formation Mechanism at the Liquid–Liquid Interface and Redox Rectification

Recent studies on molecular 2D materials with high tunability of structure and function have focused mostly on the discovery of new precursors. Here, we demonstrate a facile one‐pot synthesis of laminated 2D coordination polymer films comprising bis(terpyridine)iron and cobalt at a water/dichloromethane interface. Cross‐sectional elemental mapping unveiled the stratum‐like structure of the film and revealed that the second layer grows to the dichloromethane side below the first layer. Cyclic voltammetry clarified that the bottom layer mediates charge transfer between the top layer and the substrate in a narrow potential region of mixed‐valence states. Furthermore, the bilayer film sandwiched by electrodes in a dry condition shows stable rectification character, and the barrier voltage corresponds to the redox potential difference between the two layers. This study introduces a new strategy for polymer design to explore the materials science of molecular 2D materials.

An alternating conduction-insulation "molecular fence" model from fluorinated metallopolymers

Introducing fluoroalkyl chains into metallopolymers is a prerequisite to studying the self-organization effect of fluoroalkyl chains and their structure-property relationship. In this work, we present a fluorinated metallopolymer to build an alternating conduction-insulation "molecular fence" model synthesized by the coordination of Ru(II) and a bis-terpyridine-end-capped-phenyl (BTP) ligand modified with fluoroalkyl chains. Taking advantage of scanning tunneling microscopy (STM), a well-aligned periodic linear layered structure is observed clearly, which provides the most direct visualization of the self-organization effect of fluoroalkyl chains for the first time. In addition, combining ultraviolet-visible (UV-vis) absorption spectroscopy and theoretical calculations, we find that fluoroalkyl chains demonstrate a septation effect between two adjacent metallopolymer chains and further restrain the occurrence of interchain charge-transfer transition (ICCT) due to their closed packed structure. This "molecular fence" model can provide a novel route for electron conduction in molecular networks and guide potential applications in the materials science field.

Ultralong π-Conjugated Bis(terpyridine)metal Polymer Wires Covalently Bound to a Carbon Electrode: Fast Redox Conduction and Redox Diode Characteristics

We developed an efficient and convenient electrochemical method to synthesize π-conjugated redox metal-complex linear polymer wires composed of azobenzene-bridged bis(terpyridine)metal (2-M, M = Fe, Ru) units covalently immobilized on glassy carbon (GC). Polymerization proceeds by electrochemical oxidation of bis(4′-(4-anilino)-2,2′:6′,2″-terpyridine)metal (1-M) in a water–acetonitrile–HClO₄ solution, affording ultralong wires up to 7400 mers (corresponding to ca. 15 μm). Both 2-Fe and 2-Ru undergo reversible redox reactions, and their redox behaviors indicate remarkably fast redox conduction. Anisotropic hetero-metal-complex polymer wires with Fe and Ru centers are constructed via stepwise electropolymerization. The cyclic voltammograms of two hetero-metal-complex polymer wires, GC/[2-Fe]–[2-Ru] (3) and GC/[2-Ru]–[2-Fe] (4), show irreversible redox reactions with opposite electron transfer characteristics, indicating redox diodelike behavior. In short, the present electrochemical method is useful to synthesize polymer wire arrays and to integrate functional molecules on carbon.

Neptunium(V) Isothiocyanate Complexes with 4'-Aryl-Substituted 2,2':6',2″-Terpyridines and N,N-Dimethylacetamide as Molecular Ligands

New complexes of neptunyl(V) isothiocyanate with 4'-aryl-substituted 2,2':6',2″-terpyridines (Terpy) and N,N-dimethylacetamide (DMA) were obtained: [(NpO₂)(4'-Ph-Terpy)(DMA)(NCS)]·DMA, [(NpO₂)(4'-(4-(CF₃)C₆H₄)-Terpy)(DMA)(NCS)]·2H₂O·DMA, [(NpO₂)(4'-(3-BrC₆H₄)-Terpy)(DMA)(NCS)]·DMA, and [(NpO₂)(4'-(2-(COOH)C₆H₄)-Terpy)(DMA)(NCS)]·DMA. The structures of the compounds were determined with X-ray diffraction analysis. The neptunium coordination polyhedra were found to be pentagonal bipyramids with O atoms of the NpO₂ groups in the apical positions and the equatorial planes formed by three N atoms of the terpyridine ligand, a N atom of the isothiocyanate anion, and an O atom of DMA. The influence of the substituents of the Ar group on the crystal structure is discussed. The IR spectra contain well-resolved bands of characteristic vibrations of all groups in the complex. The electronic absorption spectra are typical for neptunium(V) complexes and contain an intense narrow absorption band belonging to an f-f transition with a maximum of 988 nm and several long-wave satellites of lower intensity. The substituted terpyridines were shown to be efficient for the extraction of various valence forms of neptunium from the isothiocyanate solutions.

Immobilizing a π-Conjugated Catecholato Framework on Surfaces of SiO2 Insulator Films via a One-Atom Anchor of a Platinum Metal Center to Modulate Organic Transistor Performance

Chemical modification of insulating material surfaces is an important methodology to improve the performance of organic field-effect transistors (OFETs). However, few redox-active self-assembled monolayers (SAMs) have been constructed on gate insulator film surfaces, in contrast to the numerous SAMs formed on many types of conducting electrodes. In this study, we report a new approach to introduce a π-conjugated organic fragment in close proximity to an insulating material surface via a transition metal center acting as a one-atom anchor. On the basis of the reported coordination chemistry of a catecholato complex of Pt(II) in solution, we demonstrate that ligand exchange can occur on an insulating material surface, affording SAMs on the SiO₂ surface derived from a newly synthesized Pt(II) complex containing a benzothienobenzothiophene (BTBT) framework in the catecholato ligand. The resultant SAMs were characterized in detail by water contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and cyclic voltammetry. The SAMs served as good scaffolds of π-conjugated pillars for forming thin films of a well-known organic semiconductor C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), accompanied by the engagements of the C8-BTBT molecules with the SAMs containing the common BTBT framework at the first layer on SiO₂. OFETs containing the SAMs displayed improved performance in terms of hole mobility and onset voltage, presumably because of the unique interfacial structure between the organic semiconducting and inorganic insulating layers. These findings provide important insight into creating new elaborate interfaces through installing coordination chemistry in solution to solid surfaces, as well as OFET design by considering the compatibility between SAMs and organic semiconductors.

Terpyridine-metal complexes: effects of different substituents on their physico-chemical properties and density functional theory studies

A series of different substituted terpyridine (tpy)-based ligands have been synthesized by Kröhnke method. Their binding behaviour was evaluated by complexing them with Co(II), Fe(II) and Zn(II) ions, which resulted in interesting coordination compounds with formulae, [Zn(tpy)₂]PF₆, [Co(tpy)₂](PF₆)₂, [Fe(tpy)₂](PF₆)₂ and interesting spectroscopic properties. Their absorption and emission behaviours in dilute solutions were investigated in order to explain structure-property associations and demonstrate the impact of different aryl substituents on the terpyridine scaffold as well as the role of the metal on the complexes. Photo-luminescence analysis of the complexes in acetonitrile solution revealed a transition from hypsochromic to bathochromic shift. All the compounds displayed remarkable photo-luminescent properties and various maximum emission peaks owing to the different nature of the functional groups. Furthermore, the anti-microbial potential of ligands and complexes was evaluated with docking analyses carried out to investigate the binding affinity of terpyridine-based ligands along with corresponding proteins (shikimate dehydrogenase and penicillin-binding protein) binding sites. To obtain further insight into molecular orbital distributions and spectroscopic properties, density functional theory calculations were performed for representative complexes. The photophysical activity and interactions between chromophore structure and properties were both investigated experimentally as well as theoretically.

Ferrocene on Insulator: Silane Coupling to a SiO2 Surface and Influence on Electrical Transport at a Buried Interface with an Organic Semiconductor Layer

A silane coupling-based procedure for decoration of an insulator surface containing abundant hydroxy groups by constructing redox-active self-assembled monolayers (SAMs) is described. A newly synthesized ferrocene (Fc) derivative containing a triethoxysilyl group designated FcSi was immobilized on SiO₂/Si by a simple operation that involved immersing the substrate in a toluene solution of the Fc silane coupling reagent and then rinsing the resulting substrate. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the Fc group was immobilized on SiO₂/Si in the Fe(II) state. Cyclic voltammetry measurements showed that the Fc groups were electrically insulated from the Si electrode by the SiO₂ layer. The FcSi on SiO₂/Si structures were found to serve as a good scaffold for formation of organic semiconductor thin films by vacuum thermal evaporation of C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), which is well-known as an organic field-effect transistor (OFET) material. The X-ray diffraction profile indicated that the conventional standing-up conformation of the C8-BTBT molecules perpendicular to the substrates was maintained in the thin films formed on FcSi@SiO₂/Si. Further vacuum thermal evaporation of Au provided an FcSi-based OFET structure with good transfer characteristics. The FcSi-based OFET showed pronounced source-drain current hysteresis between the forward and backward scans. The degree of this hysteresis was varied reversibly via gate bias manipulation, which was presumably accompanied by trapping and detrapping of hole carriers at the Fc-decorated SiO₂ surface. These findings provide new insights into application of redox-active SAMs to nonvolatile OFET memories while also creating new interfaces through junctions with functional thin films, in which the underlying redox-active SAMs play supporting roles.

Spin-crossover in iron(II)-phenylene ethynylene-2,6-di(pyrazol-1-yl) pyridine hybrids: toward switchable molecular wire-like architectures

Luminescent oligo(p-phenylene ethynylene) (OPE) and spin-crossover (SCO) active Fe(II)-2,6-di(pyrazol-1-yl) pyridine (BPP) systems are prominent examples proposed to develop functional materials such as molecular wires/memories. A marriage between OPE and Fe(II)-BPP systems is a strategy to obtain supramolecular luminescent ligands capable of metal coordination useful to produce novel spin-switchable hybrids with synergistic coupling between spin-state of Fe(II) and a physical property associated with the OPE skeleton, for example, electronic conductivity or luminescence. To begin in this direction, two novel ditopic ligands, namely L¹ and L², featuring OPE-type backbone end-capped with metal coordinating BPP were designed and synthetized. The ligand L² tailored with 2-ethylhexyloxy chains at the 2 and 5 positions of the OPE skeleton shows modulated optical properties and improved solubility in common organic solvents relative to the parent ligand L¹. Solution phase complexation of L¹ and L² with Fe(BF₄)₂·6H₂O resulted in the formation of insoluble materials of the composition [Fe(L¹)] _n (BF₄)_2n and [Fe(L²)] _n (BF₄)_2n as inferred from elemental analyses. Complex [Fe(L¹)] _n (BF₄)_2n underwent thermal SCO centred at T _1/2  =  275 K as well as photoinduced low-spin to high-spin transition with the existence of the metastable high-spin state up to 52 K. On the other hand, complex [Fe(L²)] _n (BF₄)_2n , tethered with 2-ethylhexyloxy groups, showed gradual and half-complete SCO with 50% of the Fe(II)-centres permanently blocked in the high-spin state due to intermolecular steric interactions. The small angle x-ray scattering (SAXS) pattern of the as-prepared solid complex [Fe(L¹)] _n (BF₄)_2n revealed the presence of nm-sized crystallites implying a possible methodology towards the template-free synthesis of functional-SCO nanostructures.

Electronic Properties of Oxidized Cyclometalated Diiridium Complexes: Spin Delocalization Controlled by the Mutual Position of the Iridium Centers

Four cyclometalated diiridium complexes, with IrCp*Cl (Cp*=η⁵ -C₅ Me₅ ^- ) termini bridged by 1,4- and 1,3-bis(p-tolyliminoethyl)benzene (1, 2), or 1,4- and 1,3-bis(2-pyridyl)benzene (3, 4), were prepared and characterized by nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray diffraction (complexes 1, 2, and 4). The two iridium centers in complexes 1 and 3 are thus bound at the central benzene ring in the para-position (trans-Ir2), whereas those in complexes 2 and 4 are in the meta-position (cis-Ir2). Cyclic voltammograms of all four complexes show two consecutive one-electron oxidations. The potential difference between the two anodic steps in 1 and 3 is distinctly larger than that for 2 and 4. The visible-near-infrared (NIR)-short-wave infrared (SWIR) absorption spectra of trans-Ir2 monocations 1⁺ and 3⁺ are markedly different from those of cis-Ir2 monocations 2⁺ and 4⁺ . Notably, strong near-infrared electronic absorption appears only in the spectra of 1⁺ and 3⁺ whereas 2⁺ and 4⁺ absorb only weakly in the NIR-SWIR region. Combined DFT and TD-DFT calculations have revealed that (a) 1⁺ and 3⁺ (the diiridium-benzene trans-isomers) display the highest occupied spin-orbitals (HOSO) and the lowest unoccupied spin-orbital (LUSO) evenly delocalized over both molecule halves, and (b) their electronic absorptions in the NIR-SWIR region are attributed to mixed metal-to-ligand and ligand-to-ligand charge transfers (MLCT and LLCT). In contrast, cis-isomers 2⁺ and 4⁺ do not feature this stabilizing π-delocalization but a localized mixed-valence state showing a weak intervalence charge-transfer (IVCT) absorption in the SWIR region.

Synthesis of terpyridine-containing polycarbonates with post polymerization providing water-soluble and micellar polymers and their metal complexes

Carbon dioxide based polymers synthesized from the metal-catalysed copolymeriation of epoxides and CO₂ containing the terpyridine ligand as an end group are reported.

Terpyridine-metal complexes: Applications in catalysis and supramolecular chemistry

As an NNN-tridentate ligand, the 2,2':6',2"-terpyridine plays an important role in coordination chemistry. With three coordination sites and low LUMO, terpyridine and its derivatives are one of the typical Pincer ligand and/or non-innocent ligands in transition metal catalysis. Interesting catalytic reactivities have been obtained with these tpy-metal complexes targeting some challenging transformations, such as C-C bond formation and hydrofunctionalization. On the other hand, terpyridine ligands can form "closed-shell" octahedral complexes, which provide a linear and stable linkage in supramolecular chemistry. Numerous supramolecular architectures have been achieved using modified terpyridine ligands including Sierpiński triangles, hexagonal gasket and supramolecular rosettes. This review presents a summary of recent progress regarding transition metal-terpyridine complexes with the focus on their applications in catalysis and supramolecular structure construction. Facile synthesis of terpyridine derivatives is also described. We hope this article can serve to provide some general perspectives of the terpyridine ligand and their applications in coordination chemistry.

Crystal structure of dichlorido-([2,2′:6′,2′′-terpyridine]-4′-carboxylic acid-κ3 N,N′,N′′)copper(II) monohydrate, C16H13Cl2CuN3O3

C16H13Cl2CuN3O3, monoclinic, P21/c (no. 14), a = 11.2656(9) Å, b = 17.1737(14) Å, c = 8.7774(7) Å, β = 98.1940(10)°, V = 1680.8(2) Å3, Z = 4, R gt(F) = 0.0270, wR ref(F 2) = 0.0852, T = 298(2) K.

A nano-junction of self-assembled mixed-metal-centre molecular wires on transparent conductive oxides

The fabrication of stable, highly conductive molecular nano-junctions is one of the main research goals in the field of molecular electronics. In this paper we report on the self-assembly and functional characterisation of highly conductive molecular wires, based on mixed-metal polynuclear complexes, at the surface of a transparent conductive oxide. The adopted synthetic approach involves metal-coordination reactions on oxide surfaces, pre-functionalised with a monolayer of terpyridine moieties that are used as anchoring sites for the integration of ditopic, redox-active ruthenium-bisterpyridine molecules through iron(ii) centres. By the stepwise iteration of the iron-coordination reaction, molecular wires of the desired length can be prepared, which alternate iron and ruthenium centres in the wire backbone. The stepwise assembly of the wires at the transparent conductive oxide surface was characterised by means of UV-Vis spectroscopy and, at the nanoscale, by means of ToF-SIMS measurements. The electrical characteristics of the wires were obtained by the liquid-metal eutectic-gain nano-junction technique, with results that show good electron transport capabilities along the wires. The demonstrated feasibility of the integration of these metal-polypyridinic, redox-active, conductive wires at the surface of a transparent and conductive oxide, and the evidence for good electrical conduction indicates prospective applications in the field of nanoscale molecular optoelectronics.

A combination of super-resolution fluorescence and magnetic resonance imaging using a Mn(ii) compound

Two manganese(ii) complexes supported by terpyridyl-based ligands were synthesized; they showed an enhanced fluorescence, including a two-photon signal and magnetic contrast, and were used in multi-modal imaging.

Diruthenium(ii)-capped oligothienylethynyl bridged highly soluble organometallic wires exhibiting long-range electronic coupling

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with -C[triple bond, length as m-dash]C-H termini have been successfully synthesized through stepwise Pd(0)/Cu(i)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(ii) diacetylide complexes (O1-Ru2, O3-Ru2, O5-Ru2 and O7-Ru2, respectively) have been prepared by the reaction of cis-Ru(dppe)2Cl2 and NaPF6 in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(ii)-Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(ii)-C[triple bond, length as m-dash]C-Ph]-capped diacetylide organometallic wires (O1-Ru2-Ph, O3-Ru2-Ph, O5-Ru2-Ph and O7-Ru2-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(ii)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(ii)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(ii) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.

A computational study on a multimode spin conductance switching by coordination isomerization in organometallic single-molecule junctions

Single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through molecular design. Here, we focus on a family of organometallic complexes with a conjugated curved buckybowl as the ligand. Using first-principles calculations, a multi-mode reversible spin switching based on the CpFe·corannulene complex is predicted by the temperature control of the CpFe+ coordination position in corannulene. The different spin conductance states for three coordinated modes are ascribed to the different electronic spin states of the organometallic complex due to crystal field effects. The predicted relative stabilities of isomers and the energy barriers of isomerization reactions can ensure that the conversion among the three isomers can occur quickly and, at a specific temperature, a dominant isomer has a higher proportion than the other two isomers. This provides a new framework for understanding transport in organometallic complexes with localized d states. This presents an exciting opportunity for exploiting junctions involving molecular spin switching.

Designing Optoelectronic Properties by On-Surface Synthesis: Formation and Electronic Structure of an Iron-Terpyridine Macromolecular Complex

Supramolecular chemistry protocols applied on surfaces offer compelling avenues for atomic-scale control over organic-inorganic interface structures. In this approach, adsorbate-surface interactions and two-dimensional confinement can lead to morphologies and properties that differ dramatically from those achieved via conventional synthetic approaches. Here, we describe the bottom-up, on-surface synthesis of one-dimensional coordination nanostructures based on an iron (Fe)-terpyridine (tpy) interaction borrowed from functional metal-organic complexes used in photovoltaic and catalytic applications. Thermally activated diffusion of sequentially deposited ligands and metal atoms and intraligand conformational changes lead to Fe-tpy coordination and formation of these nanochains. We used low-temperature scanning tunneling microscopy and density functional theory to elucidate the atomic-scale morphology of the system, suggesting a linear tri-Fe linkage between facing, coplanar tpy groups. Scanning tunneling spectroscopy reveals the highest occupied orbitals, with dominant contributions from states located at the Fe node, and ligand states that mostly contribute to the lowest unoccupied orbitals. This electronic structure yields potential for hosting photoinduced metal-to-ligand charge transfer in the visible/near-infrared. The formation of this unusual tpy/tri-Fe/tpy coordination motif has not been observed for wet chemistry synthetic methods and is mediated by the bottom-up on-surface approach used here, offering pathways to engineer the optoelectronic properties and reactivity of metal-organic nanostructures.

Photoactive Molecular Dyads [Ru(bpy)3-M(ttpy)2] n+ on Gold (M = Co(III), Zn(II)): Characterization, Intrawire Electron Transfer, and Photoelectric Conversion

We propose in this work a stepwise approach to construct photoelectrodes. This takes advantage of the self-assembly interactions between thiol with a gold surface and terpyridine ligands with first-row transition metals. Here, a [Ru(bpy)₃]²⁺ photosensitive center bearing a free terpyridine group has been used to construct two linear dyads on gold (Au/[Zn^II-Ru^II]⁴⁺ and Au/[Co^III-Ru^II]⁵⁺). The stepwise construction was characterized by electrochemistry, quartz crystal microbalance, and atomic force microscopy imaging. The results show that the dyads behave as rigid layers and are inhomogeneously distributed on the surface. The surface coverages are estimated to be in the order of 10^-11 mol cm^-2. The kinetics of the heterogeneous electron transfer is determined on modified gold ball microelectrodes using Laviron's formula. The oxidation rates of the terminal Ru(II) subunits are estimated to be 700 and 2300 s^-1 for Au/[Zn^II-Ru^II]⁴⁺ and Au/[Co^III-Ru^II]⁵⁺, respectively. In the latter case, the rate is limited by the kinetics of electron transfer between an intermediate Co(II) center and the gold surface. For Au/[Zn^II-Ru^II]⁴⁺, the Zn-bis-terpyridine center is not involved in the electron-transfer process and the oxidation of the Ru(II) subunit occurs through a superexchange process. In the presence of a tertiary amine in solution, the electrodes at a bias of 0.12 V behave as photoanodes when subjected to visible light irradiation. The magnitude of the photocurrent is around 10 μA cm^-2 for Au/[Co^III-Ru^II]⁵⁺ and 5 μA cm^-2 for Au/[Zn^II-Ru^II]⁴⁺, proving the importance of an electron relay on the photon-to-current conversion. The results suggest an efficient conversion for Au/[Co^III-Ru^II]⁵⁺, since each bound dyad, once excited, injects an electron around 10 times per second.

Bridged cyclometalated diruthenium complexes for fundamental electron transfer studies and multi-stage redox switching

Four bridged cyclometalated diruthenium systems are highlighted in this Frontier article, including strongly-coupled diruthenium complexes with a short phen-1,4-diyl or a planar pyren-2,7-diyl bridge, redox asymmetric diruthenium complexes characterized by different terminal ligands on the two ends, diruthenium complexes with a urea bridge that allows modulating the degree of electronic coupling, and those with a redox-active amine bridge with varying electronic structures. These complexes posess redox couples with low potentials and intense intervalence charge transfer absorptions in the near-infrared region in the one-electron-oxidized mixed-valent state. They are appealing not only for providing a platform for fundamental electron transfer studies but also as molecular materials with multi-stage redox switching properties.

Synthesis, crystal structures, one/two-photon optical properties and bioimaging application of two organic molecules with D–A and D–π–A models containing 6-phenyl-2,2′-bipyridine

The structures, one/two-photon optical properties and bioimaging application of two organic molecules with D–A and D–π–A models containing 6-phenyl-2,2′-bipyridine were studied.

Covalently Assembled Monolayers of Homo- and Heteroleptic FeII -Terpyridyl Complexes on SiOx and ITO-Coated Glass Substrates: An Experimental and Theoretical Study

Well-defined Fe^II -terpyridyl monolayers were fabricated on SiO_x and conductive ITO-coated glass substrates through covalent-bond formation between the metallo-organic complexes and a preassembled coupling layer. Three different homo- and heteroleptic complexes with terminal pyridyl, amine, and phenyl groups were tested. All the films were found to be densely packed and homogeneous, and consist of molecules standing upright. They exhibited high thermal (up to ≈220 °C) and temporal (up to 5 h at 100 °C) stability. The UV/Vis spectra of the monolayers showed pronounced metal-to-ligand charge-transfer bands with a significant redshift compared with the solution spectra of the metallo-ligands with a pendant pyridyl group quaternized with the coupling layer, whereas the shift was significantly smaller when the coupling layer was bonded to the primary amine (-NH₂ ) group of the complex. Cyclic voltammograms of the monolayers showed reversible, one-electron redox behavior and suggested strong electronic coupling between the confined molecules and the underlying substrate. Analysis of the electrochemistry data allowed us to estimate the charge-transfer rate constant between the metal center and the substrate. Additionally, detailed quantum-chemical calculations were performed to support and rationalize the experimentally observed photophysical properties of the Fe^II -terpyridyl complexes both in the solution state and when bound to a SiO_x -based substrate.

Structural origins of the cohesive energy in metal-terpyridine oligomer thin-films

Fe^II-terpyridine based oligomers have attracted considerable interest as key constituents for the realization of highly robust, ultra-thin ordered layers of metal center oligomers (MCOs) for organic electronics applications. By using molecular simulations and nanotribology investigations, we report on the origins of the surprisingly high mechanical and thermal stability in this type of MCO layers, which finds its expression in nanowear resistance values of up to 1.5 μN for the MCO films, as well as in a thermal stability of two-terminal MCO junctions to temperatures up to ∼100 °C under electrical load. A theoretical analysis of the fundamental cohesive forces among the constituents within the context of an electrostatic model reveal that the cohesive energy is essentially based on Coulomb interactions among the ionic constituents of the oligomers, leading to an estimated cohesive energy per molar mass of 0.0132 eV mol g^-1 for MCO layers that advantageously compare to the 0.0061 eV mol g^-1 reported for pentacene crystals.

Thermoresponsive Memory Behavior in Metallosupramolecular Polymer-Based Ternary Memory Devices

Thermal-sensitive materials, such as metallosupramolecular polymers, have been integrated into devices for a broad range of applications. However, the role of these materials is limited to temperature sensing and the lack of a memory function. Herein, we present novel [PolyCo-L1_xL2_y-PF₆]-based organic resistive memories (ORMs) possessing both a thermal response and ternary memory behavior with three electrical resistance states [high (HRS), intermediate (IRS), and low (LRS)]. Furthermore, the thermal behavior can be memorized by the Al/[PolyCoL1_xL2_y-PF₆]/indium-tin oxide devices. Heating and cooling the devices at a LRS results in a switch from the LRS to a HRS and further to a LRS, indicating that the thermal behavior can be efficiently memorized. Following the heating and cooling process, devices at a HRS retain their ternary memory behavior, while an unstable resistance variation behavior is observed at the IRS. We propose a possible mechanism for the thermoresponsive memory behavior, and this finding provides a guide for the design of future thermoresponsive ORMs.