Redox-addressable single-molecule junctions incorporating a persistent organic radical

The integration of radical (open-shell) species into single-molecule junctions at non-cryogenic temperatures is a key to unlocking the potential of molecular electronics in further applications. While many efforts have been devoted to this issue, in the absence of a chemical or electrochemical potential the open-shell character is lost when in contact with the metallic electrodes. Here, the organic 6-oxo-verdazyl radical, which is stable at ambient temperatures and atmosphere, has been functionalised by aurophilic 4-thioanisole groups at the 1,5-positions and fabricated into a molecular junction using the scanning tunnelling microscope break-junction technique. The verdazyl moiety retains open-shell character within the junction even at room temperature, and electrochemical gating permits in-situ reduction of the verdazyl to the closed-shell anionic state in a single-molecule transistor configuration. In addition, the bias-dependent alignment of the open-shell resonances with respect to the electrode Fermi levels gives rise to purely electronically-driven rectifying behaviour. The demonstration of a verdazyl-based molecular junction capable of integrating radical character, transistor-like switching behaviour, and rectification in a single molecular component under ambient conditions paves the way for further studies of the electronic, magnetic, and thermoelectric properties of open-shell species.

The scalable production of high-quality nanographite by organic radical-assisted electrochemical exfoliation.

One of the promising ways to produce graphene is the technology of graphite splitting or exfoliation, both by physical or mechanical and chemical, including electrochemical methods. The product of electro exfoliation is nanographite, which is transformed into multigraphene at the subsequent stage of liquid-phase mechanical and ultrasonic disintegration. This approach demonstrates a successful method of obtaining multigraphene from available graphite raw materials. Since, already at a potential of 1.23V, during the electrolysis of water on a graphite anode, the hydroxyl anion is discharged with the formation of a very active hydroxyl radical oxidizer, it is not surprising that when the graphite electro exfoliation process is overvolted at 10V, graphite oxidation products are formed. In order to control the defectiveness of the graphene lattice by oxidation products, we carried out processes of graphite exfoliation in the presence of both a number of reducing agents ascorbic acid, sodium borohydride, hydrazine hydrate, and in the presence of industrial antioxidants radical traps (2,2,6,6-tetramethylpiperidine-1-il)oxyl (TEMPO), (2,2,6,6-tetramethyl-4 oxo-piperidine-1-yl)oxyl (IPON), a mixture of 5,8,9-bis isomers[(2,2,6,6-tetramethyl - 4 oxo-piperidine-1-yl)]-{5,8,9-[1,1’- bi(cyclopentylidene)]-2,2’,4,4’- tetraene}(YARSIM-0215). It should be noted, that the best result of preventing the oxidation of nanographite in electro exfoliation technology in our studies is the ratio of carbon to oxygen (C/O) about 69.

Origin of the p-type characteristics of organic semiconductors

Organic semiconductors (OSC) are generally considered intrinsic (undoped), an assumption which underpins our understanding of the charge transport in this promising class of materials. However, this premise conflicts with a variety of experimental observations, that suggest the presence of excess holes carriers in OSCs at room temperature. Here, using a low-power plasma de-doping method, we report that trace amounts (~1015 cm-3) of oxygen-induced organic radical cations (OIORCs) are inherent in the lattice of OSCs as innate hole carriers, and that this is the origin of the p-type characteristics exhibited by the majority of these materials. This finding clarifies previously unexplained organic electronics phenomena and provides a foundation upon which to re-understand charge transport in OSCs. Furthermore, the de-doping method can eliminate the trace OIORCs, resulting in the complete disappearance of p-type behavior, while re-doping (under light irradiation in O2), reverses the process. These methods can precisely modulate key electronic characteristics (e.g., conductivity, polarity, and threshold voltage) in a nondestructive way, expanding the explorable charge transport property space for all known OSC materials. Accordingly, we conclude that our tailorable OIORC doping strategy, requiring only off-the-shelf equipment and a glovebox, will become a core technology in the burgeoning organic electronics industry.

Structural and Magnetic Studies on Nickel(II) and Cobalt(II) Complexes with Polychlorinated Diphenyl(4-pyridyl)methyl Radical Ligands

New magnetic metal complexes with organic radical ligands, [M(hfac)2(PyBTM)2] (M = NiII, CoII; hfac = hexafluoroacetylacetonato, PyBTM = (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical), were prepared and their crystal structures, magnetic properties, and electronic structures were investigated. Metal ions in [M(hfac)2(PyBTM)2] constructed distorted octahedral coordination geometry, where the two PyBTM molecules ligated in the trans configuration. Magnetic investigation using a SQUID magnetometer revealed that χT increased with decreasing temperature from 300 K in the two complexes, indicating an efficient intramolecular ferromagnetic exchange interaction taking place between the spins on PyBTM and M with J/kB of 21.8 K and 11.8 K for [NiII(hfac)2(PyBTM)2] and [CoII(hfac)2(PyBTM)2]. The intramolecular ferromagnetic couplings in the two complexes could be explained by density functional theory calculations, and would be attributed to a nearly orthogonal relationship between the spin orbitals on PyBTM and the metal ions. These results demonstrate that pyridyl-containing triarylmethyl radicals are key building blocks for magnetic molecular materials with controllable/predictable magnetic interactions.