Perylene Radical Cation Salts Research Articles

Temperature dependence of intra-stack defect spin–conduction-electron spininteraction in fluoranthene and perylene radical cation salts

The electron spin resonance line-width anisotropy and intensity areanalysed for the quasi-one-dimensional organic conductors (fluoranthene)2PF6and (perylene)2PF6·2/3tetrahydrofurane in the metallic phase above the Peierls transition temperature.Based on the bottleneck model of relaxation, the temperature dependence of theintra-stack exchange constant between conduction-electron spins and localizeddefect spins is derived and discussed.

Magnetic susceptibility and electrical conductivity of Perylene radical cation salts

Conduction electron properties of the quasi-one-dimensional conductors (PE)2XF6 X 2/3 THF, X = P, As and (PE)4(SbF6)3 (PE = perylene, THF = tetrahydrofurane) were investigated by measuring magnetic susceptibility and microwave conductivity in the temperature range from 10 K to 300 K. For quantitative analysis of the measurements a microscopic model was developed.

X-ray diffuse scattering and magnetic resonance: a study of structural phase transitions in perylene radical cation salts

The quasi-one-dimensional organic conductors di-perylene hexafluorophosphate and -antimonate undergo three and two structural phase transitions below room temperature, respectively. The unequivocal structural proof of the Peierls transition at T p in both compounds is provided by X-ray diffuse scattering experiments. The characterization of the structural phase transitions above T p is done using the analysis of X-ray patterns together with previously known ESR results. The combined techniques offer new insight into the relative displacements and rotations of the perylene stacks. The relationship between the Peierls transition and the precursor transitions is discussed.

Magnetic susceptibility and electrical conductivity of Perylene radical cation salts

The minority model was introduced to study the competition between agents with limited information. It has the remarkable feature that, as the number of strategies available to the agents increases, the collective gain made by the agents is reduced. This crowd effect arises from the fact that only a minority can profit at each moment, while all agents make their choices using the same input. We show that the properties of the model change drastically if the agents make choices based on their individual stories, keeping all remaining rules unaltered. This variation reduces the intrinsic frustration of the model, and improves the tendency towards cooperation and self organization. We finally study the stable mixing of individual and collective behavior.

Structure and phase transitions of perylene radical cation salts

The quasi-one dimensional conductors (PE) 2X · 2/3THF (PE = perylene, X = PF 6, AsF 6;THF = tetrahydrofurane) and (PE) 4 (SbF 6) 3 were studied by X-Ray scattering. For the PF 6 and AsF 6-salts the Peierls and two further structural transitions are characterized by fixed film-fixed crystal exposures. (PE) 4(SbF 6) 3 shows modulated diffuse sheets of high intensity in reciprocal space. Perylene and anion molecules form parallel separated stacks. Due to weak correlation of neighbouring anion stacks a Peierls transition is prevented.

How small can a Peierls dimerized chain be?

We predict that the minimum size of a Peierls dimerized chain with weak electron-phonon coupling can be in (sub)micrometer range and be there-fore detectable in mesoscopic systems. We suggest perylene radical cation salts as possible materials and the non-linear optical absorption as a possible technique of experimental observation.

How to measure diffusion constant and absolute susceptibility of charge carriers at the same time

Multiple spin echos can be excited for spin-1/2 systems by two radiofrequency pulses with tipping angles unequal to 180°, if the absolute magnetization is sufficiently large. If a magnetic field gradient is applied, the attenuation of the primary echo reveals the diffusion constant of these spins, whereas the ratio of primary and secondary echo amplitudes indicates the absolute magnetic susceptibility of the resonating spins. This potentiality is examined here numerically and by application of nuclear magnetic resonance to liquid samples containing protons. We analyse the complications that have to be overcome, if this technique is used for the study of the charge and spin carriers in low-symmetry quasi-one-dimensional organic conductors. Reasonable accuracy is obtained for the parameters derived for the conduction electrons of perylene radical cation salts.

Perylene radical cation salts with a five-eighths-filled conduction band: An ESR analysis.

Perylene radical cation salts with a five-eighths-filled conduction band: An ESR analysis.

The Peierls transition of Perylene radical cation salts with 2:1 stoichiometry containing tetrahydrofuran

Crystal structure, microwave conductivity and static magnetic susceptibility were analyzed for the conducting perylene (PE) radical cation salts of nominal composition (PE)2(PF6)1−x(AsF6) x ·2/3 THF for 0≦x≦1. Crystallographic phase transitions in the high-temperature metal phase were also characterized by differential scanning calorimetry and electron spin resonance. The Peierls transition occuring at 100–120 K (depending onx) and the opening of the energy gap in the semiconductor phase were determined from the magnetic data. The dependence of these properties on the size of the complex anions and the packing of the PE molecules is discussed.

Peierls Instability and Charge-Density-Wave Transport in Fluoranthene and Perylene Radical Cation Salts

Fluoranthene and perylene radical cation salts are quasi-one-dimensional conductors, which show a Peierls transition to a charge-density-wave ground state. Radical cation salts with different stoichiometries composed of the aromatic donor molecules fluoranthene (Fa = C16H10) or perylene (Per = C20H12) and the counterion X — = PF fi were investigated. We find that the temperature dependence of the electrical conductivity and the properties in the charge-density-wave ground state strongly depend on the composition of the crystals. When fluoranthene is replaced by perylene, the Peierls transition is shifted from 180 K to 120 K and the ground state energy gap decreases from values of 120-180 meV to 60-80 meV. In the charge-density-wave ground state the threshold field for nonlinear conductivity varies between 0.1 and 1 V/cm for different systems. Our results indicate that disorder, three-dimensional coupling and commensurability effects play an important role for the transport properties of these systems.

Peierls transition of perylene radical cation salts with five-eighth filled conduction band

The Peierls transition of Perylene (PE) radical cation salts ( PE) 2X 1 · 2 3 THF (nominal composition, X = (PF 6) 1− x (AsF 6) x , 0 ⪯ x ⪯ 1, THF = tetrahydrofuran) was analysed by static magnetic susceptibility (χ), radiofrequency and microwave electron spin resonance (ESR), (g-factor, line width ΔB), and microwave conductivity (σ). According to crystal structure analyses, these salts have a five-eighth filled conduction band. The opening of the energy gap at 100 – 120 K (depending on x) was determined by the analysis of χ(T). Additional phase transitions were observed and analysed by the different experimental techniques (χ(T), σ(T), g(T)). Due to the narrow ESR line in the metallic phase ( ΔB pp ≅ 15 mG), a reorientation of the PE-stacks at 162 K can be derived precisely via the g-anisotropy. In the low-temperature phase the angular and frequency dependence of the ESR lines' boardening is used in order to analyse the interaction between thermally activated conduction electrons and localized defects in these quasi-onedimensional conductors.

Restricted diffusion, relaxation and absolute magnetic susceptibility of the conduction electrons in quasi one-dimensional organic conductors

Abstract Pulsed electron spin resonance (ESR) is conveniently used for the analysis of spin dynamics in organic conductors - e.g. the derivation of spin-spin ( T 2 ) and spin-lattice ( T 1 ) relaxation times. If, in addition to the homogeneous magnetic field, a field gradient is applied, the diffusion constant ( D ) of the conduction electrons can be determined from the analysis of the echo decay. We show that restricted diffusion can be identified by analysis of the echo decay with help of Neuman's equations. An average diffusion length of 95.8μ m has been obtained for a Fluoranthene radical cation salt. For appropiate choice of the tipping angles, multiple spin echos can be observed after two excitation pulses, caused by the nonlinearity of the Bloch equations. We show for Fluoranthene and Perylene radical cation salts that their quantitative analysis allows the derivation of the conduction electrons' absolute magnetic susceptibility without sensitivity calibration of the spectrometer.

Ring-strain-modified properties of substituted perylene radical cation salts. A solid-state carbon-13 CPMAS NMR study

The authors have considered the stereochemical distortions of the molecular building blocks as a way to control the structure to properties relationships of organic conductive solids. 1,2,7,8-Tetrahydrodicyclopenta (cd,lm)perylene (CPP) and 3,4,9,10-tetramethylperylene (TMP), bearing sterically hindered substituents that involve strain-induced distortions of the perylene skeleton, have been synthesized. Two conductive radical-cation salts, CPP{sub 2}PF{sub 6}{center dot}CH{sub 2}Cl{sub 2} and TMP{sub 2}PF{sub 6}{center dot}CH{sub 2}Cl{sub 2}, have been prepared from these two strained donors by galvanostatic electrocrystallizations at {minus}20C in CH{sub 2}Cl{sub 2}. These two salts are isostructural (monoclinic, space group C{sub 2/m}). The structures consist of similar regular stacks of the almost planar donors (the bond lengths and angle values being distorted as expected) along the crystallographic c axis. The refinements of the structures have been difficult because of the disorder of the counterions and of the solvent contained in the channels between the organic stacks. Solid-state {sup 13}C CPMAS NMR, has been used to study both salts. They exhibit two different locally resolved {sup 13}C conduction electron Knight shift sets.