Nonsymmetric 6π-electron (“oxidized”) 6-oxoverdazyls have been synthesized for the first time. After formal incorporation of a hydrogen atom, the corresponding 7π-electron neutral verdazyl radical is generated. The 7π radical can undergo a further electrochemically reversible reduction to an 8π anion. Both redox processes occur at more moderate potentials than the parent verdazyl, tuning the accessible potential windows of 6π, 7π, and 8π verdazyl species.

Molecular electronics is a scientific endeavour that, for 60 years, has offered the promise of new technologies in which molecules integrate with, if not entirely replace, semiconductor electronics. En route to the attainment of these ambitious goals, central aspects underpinning the pursuit of this science have proven critical to the development of related technologies, including organic photovoltaics (OPV) and organic light-emitting diodes (OLEDs). Looking ahead, new opportunities in the field abound, from the study of molecular charge transport and the elucidation of molecular reaction mechanisms, to the development of biocompatible and degradable electronics, and the construction of novel chemical sensors with exquisite sensitivity and specificity. This article reviews historical developments in molecular electronics, with a particular focus on Australia’s contributions to the area. Australia’s current activity in molecular electronics research is also summarised, highlighting the capacity to both advance fundamental knowledge and develop new technologies. Scientific aspects considered include capabilities in: single molecule and molecular–monolayer junction measurement; spectroscopic analysis of molecular components and materials; synthetic chemistry; computational analysis of molecular materials and junctions; and the development of theoretical concepts that describe the electrical characteristics of molecular components, materials and putative device structures. Technological aspects considered include various aspects of molecular material design and implementation, such as: OPV and OLED construction, sensing technologies and applications, and power generation from heat gradients or friction. Missing capabilities are identified, and a future pathway for Australian scientific and technological development envisaged.

The reaction of 2,2 '-diiodo-1,1 '-biphenyl (1a) with ethynyl ferrocene (2) gave trace amounts of the expected 2,2 '-bis(ferrocenylethynyl)-1,1 '-biphenyl (3) together with 9-(ferrocenyl(ferrocenylethynyl)methylene)-9H-fluorene (4), formed via a cyclization process during the Sonogashira cross-coupling reaction, as the major product. In contrast, a similar reaction of the 2,2 '-diiodo-1,1 '-diphenyl ether analogue with 2 gave the anticipated 2,2 '-bis(ferrocenylethynyl) substituted product (11). Reaction of 11 with tetracyanoethylene gave its bis-[2 + 2] cycloaddition product in high yield (12), while the alkynyl motif in fluorenylidene 4 proved to be inert towards such reactions. Studies of the mechanism leading to formation of 4 using a Pd/dppf (dppf = 1,1 '-bis(diphenylphosphino)ferrocene) catalyst combination allowed for isolation of a {C = C(Fc)-PdI(dppf)} intermediate (13), which was structurally characterized by single crystal X-ray diffraction. Electrochemical investigations of 4, 11, 12 and 13 revealed a series of essentially ferrocene-based oxidation processes, which in the case of 4 and 11 could be better resolved using a non-coordinating anion based electrolyte. Electronic structure studies at the DFT level (B3LYP/def2-TZVP/CPCM(CH2Cl2) suggest that the first oxidation event in 4 can be assigned to the vinyl-bonded ferrocenyl moiety.

Reaction of [RuCl(dppe)Cp*] with the propargylic alcohols HC CC(OH)(R)Me [R = Ph (A), 4-pyridyl (B), and 4-NO2-C6H4 (C)] in the presence of NH4PF6 in MeOH, followed by treatment with base (t-BuOK) and workup under air, resulted in the unanticipated formation of the dinuclear bis(acetylide) species [{Ru(dppe)Cp*}(2){mu-C CC(R)=HC-CH=C(R)C C}] [R = Ph (2a), 4-py (2b), 4-NO2-C6H4 (2c)]. The dimeric complexes 2 containing an octa-3,5-diene-1,7-diyndiyl bridging ligand are formed through a sequence of reactions involving formation of the methyl allenylidene complexes [Ru{C=C=C(R)Me}(dppe)Cp*](+) and deprotonation to give the transient alkenylacetylide species [Ru{C CC(R)=CH2}(dppe)Cp*] (1). Oxidation of 1 affords the radical cation [1](+), which homocouples to give the dimeric ethane-bridged bis(allenylidene) [{Ru(dppe)Cp*}(2){mu-C=C=C(R)CH2-CH2C(R)=C=C}](2+) [(2-H-2)(2+)] and is deprotonated to give 2. Examples of these various intermediates have been spectroscopically observed and isolated through stoichiometric reactions and the reaction pathway mapped by in situ electrochemical (cyclic voltammetry, CV) and infrared-spectroelectrochemical (IR-SEC) measurements. The bimetallic complexes 2a-c each undergo two sequential oxidation events at low potentials, giving species characterized by IR-SEC as a strongly delocalized mixed-valence radical cations [2a-c](+) and the dicationic bis(allenylidene) species [{Ru(dppe)Cp*}(2){mu-C=C=C(R)HC=CH-C(R)=C=C}](2+) [(2a-c)(2+)]. Chemical oxidation of 2a with one or two equivalents of [FeCp2]PF6 allowed for isolation of the monocation [2a]PF6 and dication [2a][PF6](2), respectively.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Recent research progress in biodegradable materials and green processing for green electronics is comprehensively reviewed by Prashant Sonar, Aung Ko Ko Kyaw, and co-workers in article number 2001591. The biodegradable materials used for different functional layers and green/nontoxic processing for solar cells, organic field-effect transistors, light-emitting devices, and other devices are discussed in detail. Future development and a perspective of green electronics are also proposed and presented.

There is little question that the "electronic revolution" of the 20th century has impacted almost every aspect of human life. However, the emergence of solid-state electronics as a ubiquitous feature of an advanced modern society is posing new challenges such as the management of electronic waste (e-waste) that will remain through the 21st century. In addition to developing strategies to manage such e-waste, further challenges can be identified concerning the conservation and recycling of scarce elements, reducing the use of toxic materials and solvents in electronics processing, and lowering energy usage during fabrication methods. In response to these issues, the construction of electronic devices from renewable or biodegradable materials that decompose to harmless by-products is becoming a topic of great interest. Such "green" electronic devices need to be fabricated on industrial scale through low-energy and low-cost methods that involve low/non-toxic functional materials or solvents. This review highlights recent advances in the development of biodegradable materials and processing strategies for electronics with an emphasis on areas where green electronic devices show the greatest promise, including solar cells, organic field-effect transistors, light-emitting diodes, and other electronic devices.

The methyl substituents in the cationic allenylidene complexes trans-[Ru{C=C=C(Me)R}Cl(dppe)(2)]OTf ([1a-f]OTf) are readily deprotonated to give the corresponding alkenyl acetylide complexes trans-[Ru{C CC(=CH2)R}Cl(dppe)(2)] (3; R = Me (a), Ph (b), 'C5H10 (c), 4-MeS-C6H4 (a), 'C4H3S (e), 'C5H4N (f)). Similar chemistry is also observed from [Ru{C=C=C(Me)Ph}(dppe)Cp*]PF6 ([2b]PF6) and [Ru{C=C=C(Me)(4-MeS-C6H4)}(dPPe)CP*]PF6([2b]PF6), chosen to broaden the reaction scope, giving [Ru{C CC(=CH2)Ph}(dppe)Cp*] (4b) and [Ru{C CC(=CH2)(4-MeS- C6H4)}(dppe)Cp*] (4d). In turn, reactions of 3b,d and 4b,d with the [BF4](-) salt of the electrophilic tritylium [CPh3](+) cation give the functionalized allenylidene complexes trans-[Ru{C=C=C(CH2CPh3)- R}Cl(dppe)(2)]BF4 ([5b,d]BF4) and [Ru{C=C=C(CH2CPh3)R}(dppe)Cp*]BF4 ([6b,d] BF4) formed by addition of the electrophile to the remote vinylic carbon (C(delta)). Although trans-[Ru{C=C=C(CH2CPh3)Me}Cl(dppe)(2)]BF4 ([5a]BF4) could not be successfully purified from reactions of 3a with [CPh3]BF4, deprotonation of the crude product gave the Zaitsev vinyl product trans-[Ru{C CC(=CHCPh3)Me}Cl(dppe)(2)] (7a) in good yield. The initial cycloheptatrienyl adducts formed from reactions of 3b,d and 4b,d with the tropylium salt [C7H7]BF4 undergo a ring-contraction process in chloroform solutions upon exposure to air, to give the styrene-like products trans-[Ru(C=C=C(R)C(H)=CHPh}Cl(dppe)(2)]BF4 ([10b,d]BF4) and [Ru{C=C= C(R)C(H)=CHPh}(dppe)Cp*]BF4 ([11b,d]BF4)(,) through what is believed to be a radical mechanism mediated by triplet oxygen.

The formation of ‘quinoidal cumulenes’ is inferred from a series of trapping reactions using ruthenium and iron vinylidene and alkynyl precursors with a variety of nucleophilic and electrophilic species. This is illustrated in the cover artwork (designed by Brady Johnston) by the transformation of a ruthenium vinylidene complex, wherein the terminal alkyne moiety reacts with water to give a corresponding acetyl group. This intriguing process is best rationalised by the formation of an intermediate extended quinoidal cumulene. More information can be found in the Full Paper by J. M. Lynam, P. J. Low, et al. on page 7226.

In spite of the growing interest in fluorine-containing compounds, and the improvements in materials, optical and biological properties that can arise from substitution of a phenyl ring by ferrocene within a molecular scaffold, synthetic strategies that allow the efficient preparation of fluoroferrocene derivatives are scarce. Following conversion of ferrocene to fluoroferrocene, we have developed routes to fluorine-containing di-, tri-, tetra- and penta-substituted ferrocene derivatives to extend the available chemical space. Our approach is based on the identification of suitable reagents and conditions to achieve fluorine-directed deprotometalation, and exploitation of the halogen 'dance' rearrangement in the ferrocene series.

Well-ordered, tightly-packed (surface coverage 0.97 × 10-9 mol cm-2) monolayer films of 1,4-bis((4-ethynylphenyl)ethynyl)benzene (1) on gold are prepared via a simple self-assembly process, taking advantage of the ready formation of alkynyl C-Au σ-bonds. Electrochemical measurements using [Ru(NH3)6]3+, [Fe(CN)6]3-, and ferrocenylmethanol [Fe(η5-C5H4CH2OH)(η5-C5H5)] redox probes indicate that the alkynyl C-Au contacted monolayer of 1 presents a relatively low barrier for electron transfer. This contrasts with monolayer films on gold of other oligo(phenylene ethynylene) derivatives of comparable length and surface coverage, but with different contacting groups. Additionally, a low voltage transition (Vtrans = 0.51 V) from direct tunneling (rectangular barrier) to field emission (triangular barrier) is observed. This low transition voltage points to a low tunneling barrier, which is consistent with the facile electron transport observed through the C-Au contacted self-assembled monolayer of 1.

Gold nanoparticle capped organometallic molecular junctions are prepared from a single source precursor by simple self-assembly and mild thermolysis.

Nascent molecular electronic devices based on linear 'all-carbon' wires attached to gold electrodes through robust and reliable C-Au contacts are prepared via efficient in situ sequential cleavage of trimethylsilyl end groups from an oligoyne, Me3Si-(C[triple bond, length as m-dash]C)4-SiMe3 (1). In the first stage of the fabrication process, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate, which ultimately serves as the bottom electrode, using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CSiMe3 (Au|C8SiMe3). In the second stage, treatment of Au|C8SiMe3 with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH (Au|C8H). The reactive terminal C[triple bond, length as m-dash]C-H moiety in Au|C8H can be modified by 'click' reactions with (azidomethyl)ferrocene (N3CH2Fc) to introduce a redox probe, to give Au|C6C2N3HCH2Fc. Alternatively, incubation of the modified gold substrate supported monolayer Au|C8H in a solution of gold nanoparticles (GNPs), results in covalent attachment of GNPs on top of the film via a second alkynyl carbon-Au σ-bond, to give structures Au|C8|GNP in which the monolayer of linear, 'all-carbon' C8 chains is sandwiched between two macroscopic gold contacts. The covalent carbon-surface bond as well as the covalent attachment of the metal particles to the monolayer by cleavage of the alkyne C-H bond is confirmed by surface-enhanced Raman scattering (SERS). The integrity of the carbon chain in both Au|C6C2N3HCH2Fc systems and after formation of the gold top-contact electrode in Au|C8|GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal-monolayer-metal devices Au|C8|GNP featuring 'all-carbon' molecular wires were characterised by sigmoidal I-V curves, indicative of well-behaved junctions free of short circuits.

Resumen del poster presentado a la Conferencia bienal Fuerzas y Tunel, celebrada en Jaca (Espana) del 27 al 29 de junio de 2018.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Bipyridinium-containing wires give rise to molecular junctions with distinct geometries and conductance values.

Metal complexes are receiving increased attention as molecular wires in fundamental studies of the transport properties of metal|molecule|metal junctions. In this context we report the single-molecule conductance of a systematic series of d8 square-planar platinum(ii) trans-bis(alkynyl) complexes with terminal trimethylsilylethynyl (C[triple bond, length as m-dash]CSiMe3) contacting groups, e.g. trans-Pt{C[triple bond, length as m-dash]CC6H4C[triple bond, length as m-dash]CSiMe3}2(PR3)2 (R = Ph or Et), using a combination of scanning tunneling microscopy (STM) experiments in solution and theoretical calculations using density functional theory and non-equilibrium Green's function formalism. The measured conductance values of the complexes (ca. 3-5 × 10-5G0) are commensurate with similarly structured all-organic oligo(phenylene ethynylene) and oligo(yne) compounds. Based on conductance and break-off distance data, we demonstrate that a PPh3 supporting ligand in the platinum complexes can provide an alternative contact point for the STM tip in the molecular junctions, orthogonal to the terminal C[triple bond, length as m-dash]CSiMe3 group. The attachment of hexyloxy side chains to the diethynylbenzene ligands, e.g. trans-Pt{C[triple bond, length as m-dash]CC6H2(Ohex)2C[triple bond, length as m-dash]CSiMe3}2(PPh3)2 (Ohex = OC6H13), hinders contact of the STM tip to the PPh3 groups and effectively insulates the molecule, allowing the conductance through the full length of the backbone to be reliably measured. The use of trialkylphosphine (PEt3), rather than triarylphosphine (PPh3), ancillary ligands at platinum also eliminates these orthogonal contacts. These results have significant implications for the future design of organometallic complexes for studies in molecular junctions.