Modern History of Organic Conductors: An Overview

Single-Ion Magnetism of the [DyIII(hfac)4]- Anions in the Crystalline Semiconductor {TSeT1.5}●+[DyIII(hfac)4]- Containing Weakly Dimerized Stacks of Tetraselenatetracene

The oxidation of tetraselenatetracene (TSeT) by tetracyanoquinodimethane in the presence of dysprosium(III) tris(hexafluoroacetylacetonate), DyIII(hfac)3, produces black crystals of {TSeT1.5}●+[DyIII(hfac)4]- (1) salt, which combines conducting and magnetic sublattices. It contains one-dimensional stacks composed of partially oxidized TSeT molecules (formal averaged charge is +2/3). Dimers and monomers can be outlined within these stacks with charge and spin density redistribution. The spin triplet state of the dimers is populated above 128 K with an estimated singlet-triplet energy gap of 542 K, whereas spins localized on the monomers show paramagnetic behavior. A semiconducting behavior is observed for 1 with the activation energy of 91 meV (measured by the four-probe technique for an oriented single crystal). The DyIII ions coordinate four hfac- anions in [DyIII(hfac)4]-, providing D2d symmetry. Slow magnetic relaxation is observed for DyIII under an applied static magnetic field of 1000 Oe, and 1 is a single-ion magnet (SIM) with spin reversal barrier Ueff = 40.2 K and magnetic hysteresis at 2 K. Contributions from DyIII and TSeT●+ paramagnetic species are seen in EPR. The DyIII ion rarely manifests EPR signals, but such signal is observed in 1. It appears due to narrowing below 30 K and has g4 = 6.1871 and g5 = 2.1778 at 5.4 K.

Computational demonstrations of density wave of Cooper pairs and paired-electron liquid in the quarter-filled band-A brief review

There has been strong interest recently in the so-called Cooper pair density wave, subsequent to the proposition that such a state occurs in the hole-doped cuprate superconductors. As of now, there is no convincing demonstration of such a state in the cuprate theoretical literature. We present here a brief but complete review of our theoretical and computational work on the paired-electron crystal (PEC), which has also been experimentally seen in the insulating phase proximate to superconductivity (SC) in organic charge-transfer solid (CTS) superconductors. Within our theory, SC in the CTS does indeed evolve from the PEC. A crucial requirement for the finding of the PEC is that the proper carrier density of one charge carrier per two sites is taken into consideration at the outset. Following the discussion of CTS superconductors, we briefly discuss how the theory can be extended to understand the phase diagram of the cuprate superconductors that has remained mysterious after nearly four decades of the discovery of SC in this family.

Radical Cation Salts of Hetera-Buckybowls: Polar Crystals, Negative Thermal Expansion and Phase Transition

Radical cation salts of π-conjugated polycycles are rich in physical properties. Herein, two kinds of hetera-buckybowls, ethoxy-substituted trithiasumanene (3SEt) and triselenasumanene (3SeEt), are synthesized as electron donors. Galvanostatic oxidation of them affords radical cation salts (3SEt)5 (TTFMPB)3 , (3SeEt)5 (TTFMPB)3 , (3SEt)4 PMA, and (3SeEt)4 PMA, where PMA is Keggin-type phosphomolybdate and TTFMPB is tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate. In these salts, 3SEt/3SeEt are partially charged and show distinct conformation change with the site charge and counter anions. In TTFMPB salts, (TTFMPB)- forms hexagonal channels that accommodate the packing columns of 3SEt/3SeEt. In particular, (3SEt)5 (TTFMPB)3 adopts the R3c space group and is a polar crystal with the columns of 3SEt all in the up-bowl direction. The PMA salts of 3SEt/3SeEt are polar crystals (C2 space group) with 3SEt/3SeEt being planar and forming columnar stacks. (3SeEt)4 PMA shows a structural modulation below 200 K, namely, negative thermal expansion (NTE) of the unit cell volume and enlargement of the intermolecular distances between neighboring 3SeEt molecules. The four salts are semiconductors with an activation energy of 0.18-0.38 eV. The conductivity of (3SeEt)4 PMA shows a reversible transition upon cooling and heating, in accordance to the NTE structural modulation. This work paves the way toward conducting materials based on hetera-buckybowls.

A triad molecular conductor: simultaneous control of charge and molecular arrangements

Molecular and charge arrangements in the solid state were controlled by a new building block: a triad molecule. Owing to the appropriate flexibilities in both molecular structure and electron distribution of the triad, the apparently simple salt exhibits an unstable metallic phase, which is promising for superconducting transitions.

Non-Conjugated Poly(Diphenylene Phthalide)-New Electroactive Material

In organic electronics, conjugated conductive polymers are most widely used. The scope of their application is currently very wide. Non-conjugated polymers are used much less in electronics and are usually used as insulation materials or materials for capacitors. However, the potential of non-conjugated polymers is much wider, due to the fact that new electronic materials with unique electronic properties can be created on the basis of non-conjugated polymers, as well as other inorganic dielectrics. This article demonstrates the possibilities of creating electrically conductive materials with unique electronic parameters based on non-conjugated polymers. The results of the study of the sensory properties of humidity are given as examples of the practical application of the structure. The abnormal electronic properties are realized along the interface of two polymer dielectrics with functional polar groups. The submicron films of polydiphenylenephthalide were used as a dielectric. It is shown that a quasi-two-dimensional electronic structure with abnormally large values of conductivity and mobility of charge carriers occurs along the interface. These structures are often called quasi-two-dimensional electron gas (Q2DEG). This article describes the manufacturing processes of multielectrode devices. Polymer films are deposited via the spin-coating method with polymer solutions in cyclohexanone. The metal electrodes were manufactured through thermal deposition in a vacuum. Three types of metal electrodes made of aluminum, copper and chromium were used. The influence of the electron work function of contacting metals on the electronic parameters of the structure was studied. It was established that the work function decrease leads to an increase in the conductivity and mobility of charge carriers. The charge carrier parameters were estimated based on the analysis of the current-voltage characteristics within the space-charge-limited current technique. The Richardson-Schottky thermionic emission model was used to evaluate values a potential barrier at metal/organic interfaces. It was established that the change in ambient humidity strongly affects the electronic transport properties along the polymer/polymer interface. It is demonstrated that the increase in conductivity with an increase in humidity occurs due to an increase in the mobility of charge carriers and a decrease in the height of the potential barrier at the three-dimensional metal contact with two-dimensional polymer interface. The potential barrier between the electrode and the bulk of the polymer film is significantly higher than between the electrode and the quasi-two-dimensional polymer structure.

Gentle Patterning Approaches toward Compatibility with Bio-Organic Materials and Their Environmental Aspects

Advances in material science, bioelectronic, and implantable medicine combined with recent requests for eco-friendly materials and technologies inevitably formulate new challenges for nano- and micropatterning techniques. Overall, the importance of creating micro- and nanostructures is motivated by a large manifold of fundamental and applied properties accessible only at the nanoscale. Lithography is a crucial family of fabrication methods to create prototypes and produce devices on an industrial scale. The pure trend in the miniaturization of critical electronic semiconducting components has been recently enhanced by implementing bio-organic systems in electronics. So far, significant efforts have been made to find novel lithographic approaches and develop old ones to reach compatibility with delicate bio-organic systems and minimize the impact on the environment. Herein, such delicate materials and sophisticated patterning techniques are briefly reviewed.

Organic Conductors

Since the pioneering work concerning organic semiconductors in the middle of the 1900s. [...]

Theoretical Model for a Novel Electronic State in a Dirac Electron System Close to Merging: An Imaginary Element between Sulphur and Selenium

Topological materials with Dirac electron systems have been extensively studied. Organic crystalline materials form a unique group of such compounds with well-defined crystal structures. While most organic compounds require high pressures to exhibit Dirac-cone-type band structures, the title compound, α-STF2I3, has garnered increasing interest due to its Dirac-cone-type band structure under ambient pressure. Various experiments have been conducted under ambient pressure; their results can be compared with those of theoretical calculations to obtain insights into Dirac electron systems. However, structural disorder peculiar to the STF molecules in the solid-state has prevented any type of theoretical calculation of the states. In this study, we report a new method for calculating intermolecular interactions in disordered systems based on the extended Hückel approximation. This method enables band calculations, suggesting that this material is a rare example of a system close to merging. The obtained band structure indicates that the characteristic disorder in the STF solids distributed electrons equally on the sulphur and selenium atoms as if they belong to an imaginary element between sulphur and selenium and are arranged without disorder.

Large electric piezoresistance of the flexible molecular semiconductive crystal Q(TCNQ)2 during bending

Elastic and plastic molecular crystals that exhibit electrical conductivity have attracted much attention. Flexible molecular semiconductors exhibiting significant piezoresistivity can be utilized in mechanical sensors in which the application of...