Electrospun Polymer Fibers for Electronic Applications

Nano- and micro- fibers of conjugated polymer semiconductors are particularly interesting both for applications and for fundamental research. They allow an investigation into how electronic properties are influenced by size confinement and chain orientation within microstructures that are not readily accessible within thin films. Moreover, they open the way to many applications in organic electronics, optoelectronics and sensing. Electro-spinning, the technique subject of this review, is a simple method to effectively form and control conjugated polymer fibers. We provide the basics of the technique and its recent advancements for the formation of highly conducting and high mobility polymer fibers towards their adoption in electronic applications

Thiol Functionalized Diphenyl Bithiophene for Monomolecular Bistable Layers

Diphenyl bithiophene derivatives (DPBTs), known for their electrical bistable behavior, have been used in bulk resistive memory cells. In this article, we present the design and synthesis of a ω-alkyl thiol functionalized 3,3′-diphenyl 2,2′-bithiophene; such functionalization confers the ability to anchor on a metal surface, which may be conveniently applied for the development of monomolecular bistable devices

Biradicaloid Character of Thiophene-Based Heterophenoquinones: The Role of Electron–Phonon Coupling

The quinoidal versus biradicaloid character of the ground state of a series of thiophene-based heterophenoquinones is investigated with quantum-chemical calculations. The role of the ground-state electronic character on molecular structure and vibrational properties is emphasized. The vibrational activities are experimentally determined and their analysis is performed by taking advantage of the definition of a collective vibrational coordinate (the P coordinate) maximizing the electron–phonon coupling, and connecting the quinoid and the aromatic biradicaloid resonance structures. The combined experimental and computational investigation supports the biradicaloid nature of the longer oligomers. The modulation of Raman intensities and frequency dispersion, experimentally observed by increasing the length of the chromophore, is shown to be reproduced well by model calculations on a single chromophore as a function of geometry displacements along the P-mode. These results underline the role of electron–phonon coupling in governing the structure–property relationship of highly conjugated organic compounds, underscoring the similarity of thiophene heterophenoquinone systems with other, more classical, oligophenylene and oligothiophene derivatives

n-Type Semiconducting Polymer Fibers

Defect-free bicomponent fibers of poly{[N,N′-bis(2-octyl-dodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}/poly(ethyleneoxide) P(NDI2OD-T2)/PEO are fabricated by means of electrospinning and rinsed with a selective solvent to afford pure P(NDI2OD-T2) while maintaining a fibrous morphology. The elongation strength applied on the spun jet by the high electrical field induces a preferential orientation of polymer chains. An electron mobility analogous to the best obtained with a thin film-based device is achieved in single fiber transistors, and the results are unaffected by the dielectric surface treatment

Raman spectroscopic characterization of a thiophene based active material for resistive organic nonvolatile memories

A combined theoretical and experimental Raman study is presented on a diphenyl bithiophene molecule known as a good candidate for organic nonvolatile memory devices. Spectroscopic markers suitable to distinguish the different stable conformers of the molecule have been predicted and detected, thus opening the way to the identification of the molecular isomers present in the thin film of the memory cell and finally of the active molecular species involved in the switching mechanism of the operating device

Solution Processed, Versatile Multilayered Structures for the Generation of Metal-Enhanced Fluorescence

We present an all-solution processed multilayered structure completely obtained via spin-coating, which can be used to study and optimize the phenomenon of metal-enhanced fluorescence. Indeed, the electromagnetic interactions occurring between fluorescent probes and localized surface plasmons typical of metal nanoparticles (NPs), which influence the fluorescence quantum yield, are strongly dependent on the nanoparticle/molecule distance. The platform proposed here offers unique advantages in terms of processability, allowing a fine-tuning of such a distance in a single deposition step. Fluorescence versus fluorophore/AuNP spacing curves are shown for two organic systems, namely, a perylene-based dye dispersed in a polymer matrix and a polyconjugated polymer (poly(3-hexylthiophene)), interacting with a nanostructured gold thin film. In both cases, optimal distances and enhancement factors have been measured

Electronic transport regimes through an alkoxythiolated diphenyl-2,2′-bithiophene-based molecular junction diodes: Critical assessment of the thermal dependence

The detailed understanding of electronic transport through a single molecule or an ensemble of self-assembled molecules embedded between two metallic leads is still a matter of controversy. Multiple factors influence the charge transport in the molecular junction, with particular attention to be given to the band states of the electrodes, molecular orbital energies, bias potential and importantly molecule-electrode electronic coupling. Moreover it is not trivial to disentangle molecular contributions from other possible conduction pathways directly coupling the opposite electrodes. We here investigate the electronic transport properties of an ensemble molecular junction embedding an alkylthiol derivative of a diphenol substituted bithiophene (DPBT) by means of current vs. voltage and temperature dependent measurements. We explored different junction configurations using: micropores (Au//DPBT//Au and Au//DPBT-polymer conductor//Au) and conductive-atomic force microscopy (c-AFM). In all cases, we found a transition voltage VT of ∼0.35 V. The consistent presence of a similar VT in all the tested configurations is a strong, but not conclusive, indication of a molecular signature in the charge transport, which we assessed and confirmed by temperature dependent measurements. We found a transition from an incoherent resonant tunneling at low biases and close to room temperature, where transport is thermally activated with an activation energy of ∼85 meV, to a coherent tunneling at voltages higher than VT. Unlike many other molecular junctions reported in the literature, resonant conditions commonly attributed to a hopping transport regime can be found already at room temperature and very low biases for a molecule only ∼1.5 nm long. This paper is the first report to clearly show temperature activated transport through a short and not fully conjugated molecule. Moreover, we could clearly identify a regime at low temperatures and low bias where the transport mechanism is controlled by the thermal conductivity of the metal electrodes rather than the molecule. © The Royal Society of Chemistry 2015