Synthesis, Surface Morphology, Gas Sensor, DSC Technique and Third-Order Behavior of Conducting Polymer.

The compound polyaniline (Poly-ANI) with different concentrations of (H2SO4) sulfuric acid has been synthesized by the chemical polymerization method. The prepared compounds have been characterized using number of techniques including FTIR, FE-SEM, EDS and DSC. Additionally, UV-Vis spectroscopy employed for studying the linear optical properties of polymer with different acid concentrations. Third order optical nonlinearity was characterized using Z-scan at 532 nm. The results showed that the nonlinear refractive index has a negative sign. It was observed that the nonlinear refractive index changes in different ratios of H2SO4. The high value of nonlinear refractive index ([Formula: see text]) obtained along Z-axis is [Formula: see text] cm2/W, and the corresponding [Formula: see text] is 21.5 × 10-5 esu. Also, the Poly-ANI film shows the response to NH3 gas sensing in the range 20 ppm-250 ppm and can be used for NH3 sensing application.

The Applications of Solid-State NMR to Conducting Polymers. The Special Case on Polyaniline.

Polyaniline is one of the most well studied conducting polymers due to its advanced electrical, chemical, redox and morphological properties. The high conductivity of regular polyaniline, when partially oxidized and doped under acidic conditions, has been associated with the formation of unique electronic states known as polarons and bipolarons. Alternative aniline oxidation products and interesting nanotube and nanorod forms have been observed as the synthesis conditions are varied. Solid-state NMR has offered great opportunities for structural investigations and the determination of molecular dynamics in such a complex and diverse material. This review summarizes various applications of solid-state NMR techniques to polyaniline and its derivatives and the information that can be obtained by solid-state NMR.

Doping-Induced Absorption Bands in P3HT: Polarons and Bipolarons.

In this work, we focus on the formation of different kinds of charge carriers such as polarons and bipolarons upon p-type doping (oxidation) of the organic semiconductor poly(3- hexylthiophene-2,5-diyl) (P3HT). We elucidate the cyclic voltammogram during oxidation of this polymer and present spectroscopic changes upon doping in the UV/Vis/near-IR range as well as in the mid-IR range. In the low-oxidation regime, two absorption bands related to sub-gap transitions appear, one in the UV/Vis range and another one in the mid-IR range. The UV/Vis absorption gradually decreases upon further doping while the mid-IR absorption shifts to lower energy. Additionally, electron paramagnetic resonance (EPR) measurements are performed, showing an increase of the EPR signal up to a certain doping level, which significantly decreases upon further doping. Furthermore, the absorption spectra in the UV/Vis range are analyzed in relation to the morphology (crystalline vs. amorphous) by using theoretical models. Finally, the calculated charge carriers from cyclic voltammogram are linked together with optical transitions as well as with the EPR signals upon p-type doping. We stress that our results indicate the formation of polarons at low doping levels and the existence of bipolarons at high doping levels. The presented spectroscopic data are an experimental evidence of the formation of bipolarons in P3HT.

Support of polaronic states and charge carrier concentrations of YBa2Cu3O7 -y ceramics by oxygen and Mn2O3 impurity.

The influence of oxygen and Mn2O3 impurity addition intervals 0.01 ≤ x ≤ 0.30 on the basic electrical conductivity, stabilization, crystallinity quality, grain boundary couplings, structural, orbital hybridization mechanisms, and superconducting properties of YBa2Cu3O7-yMnx ceramics has extensively been analyzed by electrical resistivity, X-ray diffraction investigations, and related theoretical results. It has been found that there is a strong link between the production conditions and fundamental characteristic features. All the results deduced have enabled us to discuss the variation of electron-electron and electron-phonon interactions, order parameter for super-electrons and cooper-pairs, organization of Cu-O coordination, homogeneities of oxidation states, microscopic structural problems, electronic density states, and grain boundary couplings between the adjacent layers in the YBa2Cu3O7-y ceramics. Similarly, we have discussed the change in the formation of pairing mechanisms and bipolarons in the polarizable lattices in the microdomain clusters. The results have shown that both the presence of oxygen and optimum manganese impurity of x = 0.07 led to the enhancement in the fundamental characteristic features related to the basic physical, quantum mechanical, and thermodynamics features. Thus, the material produced at the most ideal conditions has exhibited the best orthorhombic crystal structure with the distortion degree of 6.419 × 10-3, paring mechanism, and crystallinity quality due to the development of orthorhombicity and oxygen ordering degree. Namely, the addition of optimum manganese impurity has organized the Cu-O coordination and stabilized the crystal structure as much as possible. Numerically, the sample prepared with x = 0.07 Mn ions has displayed the largest crystallite size, c-axis length, residual resistivity ratio, onset, and offset critical temperatures of 10.977, 11.723 Å, 73 nm, 98.320 K, and 100.504 K, respectively. Conversely, the same material has demonstrated the smallest oxygen ordering degree of 6.714, strain of 44.015 × 10-3, and a- and b-axis lengths of 3.792 and 3.841 Å. On the other hand, the oxygen-free annealing condition and excess manganese impurity have completely damaged the whole mechanism because of the phase transition from orthorhombic to tetragonal (structural O-T transition) crystal structure. To sum up, the oxygen and optimum manganese impurity have encouraged the YBa2Cu3O7-y superconductors to use in much more application fields. RESEARCH HIGHLIGHTS: The presence of oxygen and an optimal level of Mn2O3 impurity in YBa2Cu3O7-y superconductors improved superconducting properties. The optimal level of Mn2O3 impurity promotes standard metallic characteristics. Ideal process conditions lead to the formation of super-electrons and cooper-pairs, expanding the superconducting energy gap. Optimal conditions lead to the expansion of orthorhombic distortion symmetry and average crystallite size. The excess manganese impurity results in a metal-to-insulator transition.

Multiple reduction of 2,5-bis(borolyl)thiophene: isolation of a negative bipolaron by comproportionation.

The 2,5-bis(borolyl)thiophene 2, a conjugated acceptor-π-acceptor system, can be reduced to the monoradical anion [2](.-) , the dianion [2](2-) , and the tetraanion [2](4-) . The dianion [2](2-) was also prepared by a comproportionation reaction and features an absorption maximum in the near-IR region (λmax =800 nm), which is characteristic of a bipolaron with a quinoidal structure.

Enhancement of Electrochromic Properties of Polyaniline Induced by Copper Ions.

Driven by the urgent need for adaptive infrared (IR) electrochromic devices, the improvement in electrochromic performance based on polyaniline (PANI) conducting polymers has become an outstanding challenge. In recent years, the acid doping strategy has been proven to increase the IR modulation ability of PANI, in particular for the Bronsted acid doping. Herein, the effects of copper ions, a Lewis acid, on the structure and electrochromic properties of polyaniline were investigated. Compared to pure polyaniline, the Cu-doped PANI porous films show better IR modulation ability. With the increasing concentration of copper ions, the Cu-doped PANI porous films exhibit a trend in volcanic patterns for the emittance variation (∆ε), depending on the number of polarons and bipolarons. The optimal IR emissivity (ε) modulation obtained on Cu-doped PANI films shows the ∆ε modulation of 0.35 and 0.3 in the wavelength range of 8-14 µm and 2.5-25 µm, superior to previously reported pure sulfuric acid-doped PANI. Furthermore, a flexible IR electrochromic device was fabricated with the present Cu-doped PANI porous films. The modulation of the emittance variation varied between 0.513 and 0.834 (∆ε = 0.32 in ranges of wavelength 8-12 µm), suggesting the great potential for applications in military camouflage and intelligent IR thermal management. We believe that the results in this work will provide a novel perspective and avenue for improving the IR modulation ability of electrochromic devices based on polyaniline conducting polymers.

Driving Force and Optical Signatures of Bipolaron Formation in Chemically Doped Conjugated Polymers.

Molecular dopants are often added to semiconducting polymers to improve electrical conductivity. However, the use of such dopants does not always produce mobile charge carriers. In this work, ultrafast spectroscopy is used to explore the nature of the carriers created following doping of conjugated push-pull polymers with both F4 TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and FeCl3 . It is shown that for one particular push-pull material, the charge carriers created by doping are entirely non-conductive bipolarons and not single polarons, and that transient absorption spectroscopy following excitation in the infrared can readily distinguish the two types of charge carriers. Based on density functional theory calculations and experiments on multiple push-pull conjugated polymers, it is argued that the size of the donor push units determines the relative stabilities of polarons and bipolarons, with larger donor units stabilizing the bipolarons by providing more area for two charges to co-reside.

An Organic Borate Salt with Superior p-Doping Capability for Organic Semiconductors.

Molecular doping allows enhancement and precise control of electrical properties of organic semiconductors, and is thus of central technological relevance for organic (opto-) electronics. Beyond single-component molecular electron acceptors and donors, organic salts have recently emerged as a promising class of dopants. However, the pertinent fundamental understanding of doping mechanisms and doping capabilities is limited. Here, the unique capabilities of the salt consisting of a borinium cation (Mes2B+; Mes: mesitylene) and the tetrakis(penta-fluorophenyl)borate anion [B(C6F5)4]- is demonstrated as p-type dopant for polymer semiconductors. With a range of experimental methods, the doping mechanism is identified to comprise electron transfer from the polymer to Mes2B+, and the positive charge on the polymer is stabilized by [B(C6F5)4]-. Notably, the former salt cation leaves during processing and is not present in films. The anion [B(C6F5)4]- even enables the stabilization of polarons and bipolarons in poly(3-hexylthiophene), not yet achieved with other molecular dopants. From doping studies with high ionization energy polymer semiconductors, the effective electron affinity of Mes2B+[B(C6F5)4]- is estimated to be an impressive 5.9 eV. This significantly extends the parameter space for doping of polymer semiconductors.

Stability conditions of armchair graphene nanoribbon bipolarons.

Graphene nanoribbons are 2D hexagonal lattices with semiconducting band gaps. Below a critical electric field strength, the charge transport in these materials is governed by the quasiparticle mechanism. The quasiparticles involved in the process, known as polarons and bipolarons, are self-interacting states between the system charges and local lattice distortions. To deeply understand the charge transport mechanism in graphene nanoribbons, the study of the stability conditions for quasiparticles in these materials is crucial and may guide new investigations to improve the efficiency for a next generation of graphene-based optoelectronic devices. Here, we use a two-dimensional version of the Su-Schrieffer-Heeger model to investigate the stability of bipolarons in armchair graphene nanoribbons (AGNRs). Our findings show how bipolaron stability is dependent on the strength of the electron-phonon interactions. Moreover, the results show that bipolarons are dynamically stable in AGNRs for electric field strengths lower than 3.0 mV/Å. Remarkably, the system's binding energy for a lattice containing a bipolaron is smaller than the formation energy of two isolated polarons, which suggests that bipolarons can be natural quasiparticle solutions in AGNRs. Graphical Abstract Charge localization of bipolarons in armchair garphene nanoribbons.