Terminal Redox-Site Effect on the Long-Range Electron Conduction of Fe(tpy)2Oligomer Wires on a Gold Electrode

Asymmetrically Functionalized 1,3-Di(2-pyridyl)benzenes: Synthesis and Photophysical Studies

A convenient synthetic approach to asymmetrically functionalized 1,3-di(2-pyridyl)benzenes starting from 3-(3-bromophenyl)-1,2,4-triazines using sequential aza-Diels-Alder reactions and Stille cross-coupling is reported. Photophysical properties of the obtained compounds are studied.

Development of a universal conductive platform for anchoring photo- and electroactive proteins using organometallic terpyridine molecular wires

The construction of an efficient conductive interface between electrodes and electroactive proteins is a major challenge in the biosensor and bioelectrochemistry fields to achieve the desired nanodevice performance. Concomitantly, metallo-organic terpyridine wires have been extensively studied for their great ability to mediate electron transfer over a long-range distance. In this study, we report a novel stepwise bottom-up approach for assembling bioelectrodes based on a genetically modified model electroactive protein, cytochrome c553 (cyt c553) and an organometallic terpyridine (TPY) molecular wire self-assembled monolayer (SAM). Efficient anchoring of the TPY derivative (TPY-PO(OH)2) onto the ITO surface was achieved by optimising solvent composition. Uniform surface coverage with the electroactive protein was achieved by binding the cyt c553 molecules via the C-terminal His6-tag to the modified TPY macromolecules containing Earth abundant metallic redox centres. Photoelectrochemical characterisation demonstrates the crucial importance of the metal redox centre for the determination of the desired electron transfer properties between cyt and the ITO electrode. Even without the cyt protein, the ITO-TPY nanosystem reported here generates photocurrents whose densities are 2-fold higher that those reported earlier for ITO electrodes functionalised with the photoactive proteins such as photosystem I in the presence of an external mediator, and 30-fold higher than that of the pristine ITO. The universal chemical platform for anchoring and nanostructuring of (photo)electroactive proteins reported in this study provides a major advancement for the construction of efficient (bio)molecular systems requiring a high degree of precise supramolecular organisation as well as efficient charge transfer between (photo)redox-active molecular components and various types of electrode materials.

Sensitised lanthanide luminescence using a RuII polypyridyl functionalised dipicolinic acid chelate

A visible light absorbing [RuII(tpy)2]2+-type chromophore appended with a dipicolinic acid LnIII chelator has been prepared and complexed with several differing lanthanide cations to form the corresponding heterobimetallic d-f assemblies. The subseqent solution speciation analysed by 1H NMR spectroscopy revealed an unexpected decrease in the LnIII chelate complex stability, in particular for the 1 : 3 complex, when compared to the parent dipicolinic acid. As a result, the desired Ln(ML)3 complexes could not be isolated, and the 1 : 1 LnIII-ML complexes were instead characterised and investigated using steady state absorption and emission spectroscopy. Sensitised NIR emission from the YbIII, NdIII and ErIII complexes was observed upon 1MLCT excitation of the RuII based metalloligand in the visible region at ca. 485 nm. Investigations using transient absorption spectroscopy revealed essentially quantitative intersystem crossing to form the 3MLCT excited state, as expected, which then acts as the energy donor for the metalloligand based antennae effect, facilitating sensitisation efficiencies of 4.8, 17.0 and 37.4% respectively for the YbIII, ErIII and NdIII cations.

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.

A fast-switching electrochromic device with a surface-confined 3D metallo-organic coordination assembly

Demonstrated herein is a fast (<1 s)-switching solid-state electrochromic device (t = 0.49 s for coloration and 0.90 s for bleaching), fabricated with a novel imidazolium-linked [Fe(terpyridine)2]2+ chromophore-based surface-confined three dimensional metallo-organic coordination assembly. The device also exhibits promising electrochromic attributes such as high coloration efficiency (η = 275 cm2 C-1), moderate operating voltage (from -2 V to +3.2 V) and transmittance contrast (ΔT = 40%), and high cycling stability (up to 4500 cycles).

Systematic investigation of the antiproliferative activity of a series of ruthenium terpyridine complexes

Due to acquired resistance or limitations of the currently approved drugs against cancer, there is an urgent need for the development of new classes of compounds. Among others, there is an increasing attention towards the use of Ru(II) polypyridyl complexes. Most studies in the literature were made on complexes based on the coordination of N-donating bidentate ligands to the ruthenium core whereas studies on 2,2':6', 2″-terpyridine (terpy) coordinating ligands are relatively scare. However, several studies have shown that [Ru(terpy)2]²⁺ derivatives are able bind to DNA through various binding modes making these compounds potentially suitable as chemotherapeutic agents. Additionally, light irradiation of these compounds was shown to enable DNA cleavage, highlighting their potential use as photosensitizers (PSs) for photodynamic therapy (PDT). In this work, we present the systematic investigation of the potential of 7 complexes of the type [Ru(terpy)(terpy-X)]2+ (X = H (1), Cl (2), Br (3), OMe (4), COOH (5), COOMe (6), NMe2 (7)) as potential chemotherapeutic agents and PDT PSs. Importantly, six of the seven complexes were found to be stable in human plasma as well as photostable in acetonitrile upon continuous light irradiation (480 nm). The determination of the distribution coefficient logP values for the 7 complexes revealed their good water solubility. Complex 7 was found to be cytotoxic in the micromolar range in the dark as well as to have some phototoxicity upon light exposure at 480 nm in non-cancerous retinal pigment epithelium (RPE-1) and cancerous human cervical carcinoma (HeLa) cells. SYNOPSIS: The systematic investigation of the potential of 7 complexes of the type [Ru(terpy)(terpy-X)]²⁺ (terpy: 2,2':6', 2″-terpyridine; X = H (1), Cl (2), Br (3), OMe (4), COOH (5), COOMe (6), NMe2 (7)) as potential chemotherapeutic agents and photosensitizers for photodynamic therapy is presented.

Luminescent properties of a 3,5-diphenylpyrazole bridged Pt(ii) dimer

We report the synthesis, electrochemistry, photophysics and electroluminescence of a highly luminescent pyrazolate-bridged platinum(ii) complex. Light-emitting electrochemical cells (LEECs) of this dimer complex were among the brightest and most efficient LEECs from dinuclear compounds to date.

π-Conjugated bis(terpyridine)metal complex molecular wires

Bottom-up approaches have gained significant attention recently for the creation of nano-sized, ordered functional structures and materials. Stepwise coordination techniques, in which ligand molecules and metal sources are reacted alternatively, offer several advantages. Coordination bonds are stable, reversible, and self-assembling, and the resultant metal complex motifs may contain functionalities unique to their own characteristics. This review focuses on metal complex wire systems, specifically the bottom-up fabrication of linear and branched bis(terpyridine)metal complex wires on electrode surfaces. This system possesses distinct and characteristic electronic functionalities, intra-wire redox conduction and excellent long-range electron transport ability. This series of comprehensive studies exploited the customizability of bis(terpyridine)metal complex wires, including examining the influence of building blocks. In addition, simple yet effective electron transfer models were established for redox conduction and long-range electron transport. A fabrication technique for an ultra-long bis(terpyridine)metal complex wire is also described, along with its properties and functionalities.

Rapid Electron Transport Phenomenon in the Bis(terpyridine) Metal Complex Wire: Marcus Theory and Electrochemical Impedance Spectroscopy Study

The authors reported previously that bis(terpyiridne)iron(II) complex oligomer wires possess outstanding long-range intrawire electron transport ability. Here, molecular arrays of gold-electrode-bis(terpyridine)iron(II)-ferrocene are constructed by stepwise coordination as simple models of the oligomer wire system. The fast electron transfer between the terminal ferrocene and the gold electrode through the bis(terpyiridne)iron(II) complex unit is studied by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS). Tafel plots derived from PSCA are analyzed based on Marcus theory. The plots reveal greater first-order electron transfer rate constant, weaker electronic coupling between the terminal ferrocene and the gold electrode, and smaller reorganization energy than shown by a conventional ferrocenylalkanethiol self-assembled monolayer. The electron transfer rate constants estimated by EIS agree with the PSCA results.

Electron transport dynamics in redox-molecule-terminated branched oligomer wires on Au(111)

Dendritic bis(terpyridine)iron(II) wires with terminal ferrocene units were synthesized on a Au(111) surface by stepwise coordination using a three-way terpyridine ligand, a ferrocene-modified terpyridine ligand, and Fe(II) ions. Potential-step chronoamperometry, which applied overpotentials to induce the redox of the terminal ferrocene, revealed an unusual electron-transport phenomenon. The current-time profile did not follow an exponential decay that is common for linear molecular wire systems. The nonexponentiality was more prominent in the forward electron-transport direction (from the terminal ferrocene to the gold electrode, oxidation) than in the reverse direction (from the gold electrode to the terminal ferrocenium, reduction). A plateau and a steep fall were observed in the former. We propose a simple electron transport mechanism based on intrawire electron hopping between two adjacent redox-active sites, and the numerical simulation thereof reproduced the series of "asymmetric" potential-step chronoamperometry results for both linear and branched bis(terpyridine)iron(II) wires.