Double-Gate Light-Emitting Electrochemical Transistor: Confining the Organic p–n Junction

In conventional light-emitting electrochemical cells (LECs), an off-centered p–n junction is one of the major drawbacks, as it leads to exciton quenching at one of the charge-injecting electrodes and results in performance instability. To combat this problem, we have developed a new device configuration, the double-gate light-emitting electrochemical transistor (DG-LECT), in which the location of the light-emitting p–n junction can be precisely defined via the position of the two gate terminals. Based on a planar LEC structure, two gate electrodes made from an electrochemically active conducting polymer are employed to predefine the p- and n-doped area of the light-emitting polymer. Thus, a p–n junction is formed in between the p-doped and n-doped regions. We demonstrate a homogeneous and centered p–n junction as well as other predefined junction patterns in these DG-LECT devices. Additionally, we report an electrical model that explains the operation of the DG-LECTs. The DG-LECT device provides a new tool to study the fundamental physics of LECs, as it dissects the key working process of LEC into decoupled p-doping, n-doping, and electroluminescence

Organic Reprogrammable Circuits Based on Electrochemically Formed Diodes

We report a method to construct reprogrammable circuits based on organic electrochemical (EC) p–n junction diodes. The diodes are built up from the combination of the organic conjugated polymer poly­[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] and a polymer electrolyte. The p–n diodes are defined by EC doping performed at 70 °C, and then stabilized at −30 °C. The reversible EC reaction allows for in situ reprogramming of the polarity of the organic p–n junction, thus enabling us to reconfigure diode circuits. By combining diodes of specific polarities dedicated circuits have been created, such as various logic gates, a voltage limiter and an AC/DC converter. Reversing the EC reaction allows in situ reprogramming of the p–n junction polarity, thus enabling reconfiguration of diode circuits, for example, from an AND gate to an OR gate. The reprogrammable circuits are based on p–n diodes defined from only two layers, the electrodes and then the active semiconductor:electrolyte composite material. Such simple device structures are promising for large-area and fully printed reconfigurable circuits manufactured using common printing tools. The structure of the reported p–n diodes mimics the architecture of and is based on identical materials used to construct light-emitting electrochemical cells (LEC). Our findings thus provide a robust signal routing technology that is easily integrated with traditional LECs

Guanine and 8‑Azaguanine in Anomeric DNA Hybrid Base Pairs: Stability, Fluorescence Sensing, and Efficient Mismatch Discrimination with α‑d‑Nucleosides

The α-anomers of 8-aza-2′-deoxyguanosine (<b>αG</b>_<b>d</b>*) and 2′-deoxyguanosine (<b>αG</b>_<b>d</b>) were site-specifically incorporated in 12-mer duplexes opposite to the four canonical DNA constituents dA, dG, dT, and dC. Oligodeoxyribonucleotides containing <b>αG</b>_<b>d</b>* display significant fluorescence at slightly elevated pH (8.0). Oligodeoxyribonucleotides incorporating β-anomeric 8-aza-2′-deoxyguanosine (<b>G</b>_<b>d</b>*) and canonical dG were studied for comparison. For <b>αG</b>_<b>d</b>* synthesis, an efficient purification of anomeric 8-azaguanine nucleosides was developed on the basis of protected intermediates, and a new <b>αG</b>_<b>d</b><b>*</b> phosphoramidite was prepared. Differences were observed for sugar conformations (<i>N</i> vs <i>S</i>) and p<i>K</i>_a values of anomeric nucleosides. Duplex stability and mismatch discrimination were studied employing UV-dependent melting and fluorescence quenching. A gradual fluorescence change takes place in duplex DNA when the α-nucleoside <b>αG</b>_<b>d</b><b>*</b> was positioned opposite to the four canonical β-nucleosides. The strongest fluorescence decrease appeared in duplexes incorporating <b>αG</b>_<b>d</b>*-<b>C</b>_<b>d</b> base pair matches. Decreasing fluorescence corresponds to increasing <i>T</i>_m values. For mismatch discrimination, the α-anomers <b>αG</b>_<b>d</b>* and <b>αG</b>_<b>d</b> are more efficient than the corresponding β-nucleosides. Duplexes with single “purine–purine” <b>αG</b>_<b>d</b>*-<b>αG</b>_<b>d</b>* or <b>αG</b>_<b>d</b>-<b>αG</b>_<b>d</b> base pairs are significantly more stable than those displaying β-d configuration. CD spectra indicate that single mutations by α<b>-</b>anomeric nucleosides do not affect the global structure of B-DNA

Spatial Control of p–n Junction in an Organic Light-Emitting Electrochemical Transistor

Low-voltage-operating organic electrochemical light-emitting cells (LECs) and transistors (OECTs) can be realized in robust device architectures, thus enabling easy manufacturing of light sources using printing tools. In an LEC, the p–n junction, located within the organic semiconductor channel, constitutes the active light-emitting element. It is established and fixated through electrochemical p- and n-doping, which are governed by charge injection from the anode and cathode, respectively. In an OECT, the electrochemical doping level along the organic semiconducting channel is controlled via the gate electrode. Here we report the merger of these two devices: the light-emitting electrochemical transistor, in which the location of the emitting p–n junction and the current level between the anode and cathode are modulated via a gate electrode. Light emission occurs at 4 V, and the emission zone can be repeatedly moved back and forth within an interelectrode gap of 500 μm by application of a 4 V gate bias. In transistor operation, the estimated on/off ratio ranges from 10 to 100 with a gate threshold voltage of −2.3 V and transconductance value between 1.4 and 3 μS. This device structure opens for new experiments tunable light sources and LECs with added electronic functionality

Pd(II)-Directed Encapsulation of Hydrogenase within the Layer-by-Layer Multilayers of Carbon Nanotube Polyelectrolyte Used as a Heterogeneous Catalyst for Oxidation of Hydrogen

A metal-directed assembling approach has been developed to encapsulate hydrogenase (H₂ase) within a layer-by-layer (LBL) multilayer of carbon nanotube polyelectrolyte (MWNT-PVPMe), which showed efficient biocatalytic oxidation of H₂ gas. The MWNT-PVPMe was prepared via a diazonium process and addition reactions with poly­(4-vinylpyridine) (PVP) and methyl iodide (MeI). The covalently attached polymers and organic substituents in the polyelectrolyte comprised 60–70% of the total weight. The polyelectrolyte was then used as a substrate for H₂ase binding to produce MWNT-PVPMe@H₂ase bionanocomposites. X-ray photoelectron spectra revealed that the bionanocomposites included the elements of Br, S, C, N, O, I, Fe, and Ni, which confirmed that they were composed of MWNT-PVPMe and H₂ase. Field emission transmission electron microscope images revealed that the H₂ase was adsorbed on the surface of MWNT-PVPMe with the domains ranging from 20 to 40 nm. Further, with the use of the bionanocomposites as nanolinkers and Na₂PdCl₄ as connectors, the (Pd/MWNT-PVPMe@H₂ase)_<i>n</i> multilayers were constructed on the quartz and gold substrate surfaces by the Pd­(II)-directed LBL assembling technique. Finally, the as-prepared LBL multilayers were used as heterogeneous catalysts for hydrogen oxidation with methyl viologen (MV²⁺) as an electron carrier. The dynamic processes for the reversible color change between blue-colored MV⁺ and colorless MV²⁺ (catalyzed by the LBL multilayers) were video recorded, which confirmed that the H₂ase encapsulated within the present LBL multilayers was of much stronger stability and higher biocatalytic activity of H₂ oxidation resulting in potential applications for the development of H₂ biosensors and fuel cells

Fig 16 -

Spatial and temporal evolution of fracture point of similar material test block: (a) ratio 1 (b) ratio 2 (c) ratio 3.</p

Inversion of sandstone fracture point based on acoustic emission energy.

Inversion of sandstone fracture point based on acoustic emission energy.</p

Mechanical performance parameters of similar materials with different proportions.

Mechanical performance parameters of similar materials with different proportions.</p

Force and displacement in sandstone uniform loading.

Force and displacement in sandstone uniform loading.</p

Fig 7 -

Force and displacement in variable lower limit step loading of similar materials: (a) ratio 1 (b) ratio 2 (c) ratio 3.</p