Organic semiconductors: optical magnetic and electrical properties of 1-methyl-3-propylimidazolium 7,7,8,8-tetracyano-p-quinodimethane

Electrical conductivity and spectral properties (UV VIS absorption and especially the temperature dependence of IR absorption) are studied for the simple salt 1-methyl-3-propyl-imidazolium 7,7,8,8-tetracyano-p-quinodimethane (MPI⁺ TCNQ⁻. The temperature dependence of the IR absorption coefficient for the bands due to activation of the mode A_g is discussed in terms of changes in energy level population, geometry, and electron interactions. The temperature dependence of the absolute number of the TCNQ dimers in the triplet state is measured independently using the EPR method. The temperature dependences of the ground (singlet) state population of the TCNQ dimers and of the singlet—triplet energy separation J(T) = [(0.18 ± 0.01)-(2.5 ± 0.5) × 10⁻⁴ T] eV were determined from this measurement. These values lead to an unrealistically large value of the linear temperature expansion coefficient within the framework of the simple isolated model of dimers. Therefore, the weakly interacting model of dimers should be preferred. The activation energy of the triplet state exchange frequency. E_W = 0.27 eV, and the room temperature jumping frequency of the exciton along the TCNQ stacks, ν_j = 5 × 10¹⁰ s⁻¹, were determined from EPR measurements of the width of triplet lines.     

Conformational study of 1,2-dithiacyclononane

The temperature dependence of the Raman spectrum of 1,2-dithiacyclononane (1,2-DTCN) in the SS stretching region has been used to infer the existence of a conformational equilibrium with ΔH⁰ = 5.0 ± 0.8 kJ/mol. Molecular mechanics calculations predict a (2 2 5)-C₂ lowest energy conformation in equilibrium with a (2 3 4) structure. The fully decoupled ¹³C NMR spectrum at −80°C and the Raman spectra are consistent with this postulate. The temperature dependence of the ¹H NMR spectrum of 1,2-DTCN is characteristic of the ring inversion process. A crude lineshape analysis allows us to calculate ΔG⁰ = 49.0 ± 1.2 kJ/mol.     

Molecular beam chemiluminescence XI: kinetic and internal energy dependence of the NO + O3 → NO2*,→ NO23 reaction

Seeded supersonic NO beams were used to study the kinetic energy dependence of both the electronic (NO₂^*) and vibrational (NO₂³) chemiluminescence of the NO + O₃ reaction. In addition the electronic CL is found to be enhanced by raising the NO internal temperature. This is shown to be due to enhanced reactivity of the NO(²Π,_{$\text{3}\text{2}$}) fine structure component. By difference NO(²Π_{$\text{1}\text{2}$}) is concluded to yield predominantly groundstate NO₂³. The excitation function for NO₂^* formation from NO(²Π_{$\text{3}\text{2}$}) is of the form σ_{$\text{3}\text{2}$}(E) = C(E/E₀ - 1)ⁿ over the 3–6 kcal energy range where n = 2.4 ± 0.15, C = 0.163 Ų and E₀ = 3.2 ± 0.3 kcal/mole. Vibrational IR emission from NO₂³ has an energy dependence different from electronic NO₂^* emission, confirming that emitters are formed predominantly in distinct reaction channels rather than via a common precursor (either NO₂^* or NO₂³). The short wavelength cutoff of the CL spectra recorded at elevated collision energies E ? 15 kcal/mole corresponds to the total available energy. These and literature results are discussed in the light of general properties of the (generally unknown) ONO₃ potential energy surfaces. The formation of electronically excited NO₂^* rather than energetically preferred O₂ (¹ Δg) (Gauthier and Snelling) can be rationalized in terms of surface hopping near a known intersection of potential energy surfaces more easily than by vibronic interaction in the asymptotic NO₂ product.     

Laser isotope separation and the multiphoton dissociation of formic acid using a pulsed HF laser

The focussed beam from a single line [P₂ (5)] of a pulsed HF laser has been used to stimulate the decomposition of formic acid. The yield (Y is the number of product molecules per pulse / formic acid pressure) of the non-condensable (77 K) products, hydrogen and CO, has been studied as a function of laser radiant energy (from 25-115 mJ) and pressure (from 0.4-2.7 kPa). The intensity dependence of Y suggests that each dissociating formic acid requires the equivalent of at least 6 HF P₂(5) photons (260 kJ/mole). For pressures above about 0.6 kPa, Y_H2 = (?0.6 ± 1.7) × 10¹² + (2.4 ± 1.0) × 10¹² P and Y_CO = (?0.5 ± 6.1) × 10¹³ × (8.7 ± 3.7) × 10¹³ P. The linear dependerrce of yields indicates that a collisionally assisted decomposition process is important at these pressures. The efficiency of the conversion of photon energy to reaction products at a pressure of 2.7 kPa is ? 7% for CO and ? 0.2% for hydrogen. Selective excitation of HCOOH in equimolar mixtures of HCOOH/HCOOD, at a total pressure of 0.6 kPa, has provided a physically separated product, hydrogen gas, which is isotopically enriched in H versus D 25 fold as compared to the formic acid mixture. The degree of enrichment decreases as the total pressure of the mixture is increased. A possible mechanism accounting for isotope enrichment and the collisionally assisted dissociation is outlined.     

Temperature dependence of the probabilities of VV energy exchange between H2 and DCl

The temperature dependence of the removal of the vibrational energy of H₂ by DCl in H₂(1) + DCl(0) has been investigated over the range of 300–3000 K. The energy transfer probability of H₂(1) + DCl(0) → H₂(0) + DCl(1), where the vibrational energy of H₂(1) is removed by both the vibrational and rotational motions of DCl(0), is found to be strongly temperature dependent and increases with temperature closely following the relation log P α T^1/3. Over the temperature range it changes by two orders of magnitude. The probability of the near-resonant process H₂ (1) + DCl(O) → H₂(0) + DCl(2) is very close to that of the former at 300 K, but it increases only slightly as the temperature is raised to 3000 K. The sum of the probabilities of these two processes at 300 K is 3.4 × 10^?5, which agrees with the experimental value of 3.95 × 10^?5.     

Binding of anticancer drug Ru(η 6 -C6H5(CH2)2OH)Cl2(DAPTA) to DNA purine bases and amino acid residues: a theoretical study

The hydrolyzed Ru(η ⁶ -C₆H₅(CH₂)₂OH)Cl₂(DAPTA) (DAPTA = 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) binding to guanine(G), adenine (A), cytosine(C), cysteine (Cys), and histidine (His) residues were explored using the B3LYP hybrid functional and IEF-PCM solvation models. The computed activation barriers for the reactions of diaqua complex were lower than those of chloroaqua complex except for binding to cytosine. For the chloroaqua complex, the activation free energy was lowest when binding to cytosine (10.5 kcal/mol). Whereas, the substitution reaction of diaqua complex binding to cysteine showed the lowest activation free energy with 10.1 kcal/mol, closely followed by histidine (15.8 kcal/mol), adenine (20.1 kcal/mol), cytosine (20.7 kcal/mol), and guanine (24.4 kcal/mol) by turns. It could be deduced that the completely hydrolyzed Ru(η ⁶ -C₆H₅(CH₂)₂OH)Cl₂(DAPTA) compounds might preferentially bind to amino acids residues in vivo. In addition, to simulate the protein and DNA environment in vivo, a detailed investigation of the activation free energies for the substitution reactions in dependence of the dielectric constant ε (4, 24, and 78.39) was systematically performed as well. The calculated results demonstrated that the environmental effect had a little impact on these substitution reactions.     

Benchmark measurement of iodobenzene ion fragmentation rates

The unimolecular fragmentation rate of iodobenzene ion has been studied by variable residence time photoelectronphotoion coincidence techniques. The techniques employed variable wavelength with threshold photoelectron detection and fixed (58.4 nm) wavelength with variable energy photoelectron detection, respectively. Residence times of 1.0 = 0.25 or 5.9 ± 0.3 and 21 ± 1 or 57 ± 1 μs were employed. The four sets of measurements were independently analyzed using exact counting of harmonic oscillator states, taking into account the appropriate (and different) apparatus functions and the thermal energy distributions of the parent ions. The resulting rate-energy dependences and fragmentation threshold values were in excellent agreement with one another. The best-fit rate-energy dependence is proposed as a benchmark for calibration of future rate-energy measurements. The resulting ΔH_fD⁰ (C₆H₅⁺) = 1133 ± 5 kJ mol is in excellent agreement with earlier results based on a somewhat simpler method of analysis of chlorobenzene and bromobenzene fragmentation rates. Some remaining uncertainties regarding the transition-state model are discussed.     

Calculation of the nmr relaxation time of dilute 129 Xe gas

The spin-lattice relaxation time T₁ of ¹²⁹ Xe gas is calculated with the kinetic theory due to Chem and Snider. A Lennard-Jones (12,6) potential functions is employed as a model for the spherical potential while the transient spin-rotation interaction is assumed to be responsible for the relaxation of the nuclei. Cross sections for spin transitions on collisions are calculated either quantum mechanically or semiclassically depending on the relative energy. The temperature dependence of T₁ is determined in the range 200–450 K. The calculated value of T₁ at 298 K and 1 amagat is 2.8 x 0⁵ s while the value measured by Hund and Carr is (2.0 ± 0.2) x 10⁵s.     

Viscosity of concentrated solutions of polystyrene and poly(vinyl acetate) (empirical equations)

The viscosity of solutions of polystyrene with M _w from 2.8 × 10⁴ to 7.8 × 10⁵ in toluene and of poly(vinyl acetate) with M _w from 2 × 10⁴ to 1.4 × 10⁵ in butyl acetate at 30–80°C is measured. The dependence of the activation energy of the viscous flow of the solutions on the molecular weight of the polymers and solution concentration is examined. This dependence is approximated by a cubic polynomial for polystyrene solutions and by a quadratic polynomial for poly(vinyl acetate) solutions. The dependences of the solution viscosity on the concentration, molecular weight, and temperature are approximated by exponential equations in which the exponents are sums of polynomials. The coefficients of the polynomials are determined.     

Thermodynamic properties and oxygen stoichiometry of Ba2Cu3O5 + δ

The thermodynamic properties and oxygen stoichiometry of Ba₂Cu₃O_{5 + δ} are studied by means of the electromotive force (EMF) with a fluoride electrolyte, dissolution calorimetry, and thermogravimetry. It is shown that the temperature dependence of the Gibbs energy of the formation of barium cuprate from simple oxides and oxygen in the temperature range of 860–1120 K can be described by the polynomial Δ_{f, ox} G ^°(Ba₂Cu₃O_{5 + δ}) ± 0.1 (kJ/mol) = ?291.78 + 1.127T ? 0.13207 TlnT (kJ/mol).     

Effect of in impurity on crystallization kinetics of (Se.7Te.3)100−xInx system

The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se₇Te₃) have been studied by DTA measurements at different heating rates (α=5 deg·min^?1, 10 deg·min^?1, 15 deg·min^?1 and 20 deg·min^?1). From the heating rate dependence of the values ofT _g,T _c andT _p, the glass transition activation energy (E _t) and the crystallization activation energy (E _c) have been obtained for different compositions of (Se₇Te₃)_100?xIn_x (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence ofT _g and crystallization kinetics are discussed in terms of the modification of the structure of the Se?Te system.     

THE MECHANISM OF THE 9,10-DIBROMOANTHRACENE MEDIATED TRIPLET-SINGLET ENERGY TRANSFER IN THE TETRAMETHYL-1,2-DIOXETANE ENERGIZED RUBRENE LUMINESCENCE*

Abstract— The ternary chemiluminescent system consisting of tetramethyl-dioxetane (TMD), 9 ,10-dibromoanthracene (DBA) and rubrene (Ru) has been investigated in benzene solution and in polystyrene matrices. DBA has been found to mediate the energy transfer between excited triplet acetone (³K), generated from TMD, and rubrene resulting in the enhancement of the Ru emission and reduction in the DBA emission. A detailed kinetic analysis confirms that ca. 50% of the enhanced chemilumines-cence involves triplet-singlet (TS) energy transfer from ³K to DBA, followed by singlet-singlet (SS) energy transfer from DBA to Ru, the remainder ca. 50% being due to reabsorption of DBA fluorescence by rubrene. It is concluded that the TS energy transfer is of the resonance type, occurring with a rate of k^TS_K.DBA= (1.4 ± 0.4) ± 10⁹M^-1s^-1 and an efficiency of ø^TS_K.DBA= 0.3 ± 0.1. As expected, the SS energy transfer is also of the resonance type, taking place at comparable rates in benzene solution and in polystyrene matrices, is. k^SS_DBARU= 1.5 ± 10¹⁰ M^-1 and (2.2 ± 0.2) ± 10¹⁰M^-1s^-1, respectively.     

Zeolite-supported tetramethyl-1,2-dioxetane: new pathways to chemiluminescence

The thermal decomposition of tetramethyl-1,2-dioxetane (TMD) sorbed into zeolite Y containing Eu³⁺ ions and 2,2'-bipyridine (samples abbreviated as ZYEBT) has been investigated. Decomposition of TMD yields, by energy transfer processes, chemiluminescence (CL) characteristic of the Eu³⁺ ion. At loading levels corresponding to an upper-limit average of 0.5, 1.0, and 2.0 TMD molecules per unit cell, the CL decay curves are nonexponential at short times; at longer times,roughly exponential curves are characterized by a unimolecular rate constant k. Analyses of the longtime decays based on an Arrhenius expression for the rate constant provide evidence for a kinetic compensation effect : plots of log k vs. the activation energy E_a as a function of TMD loading level are linear. Solution data (benzene, benzonitrile) fall on the same line, suggesting that TMD decomposes by a common rate-limiting mechanism in these various environments. The Arrhenius parameters (E_a and the pre-exponential factor A) are smaller than the solution values and increase with TMD loading. When TMD is sorbed to the extent of an upper-limit average of ~7 molecules per unit cell, CL decay curves are initially nearly flat and then show an increase in decomposition rate with time. Mechanistic implications of these results are discussed.     

Transition metal dichalcogenides (MoS2, MoSe2, WS2 and WSe2) exfoliation technique has strong influence upon their capacitance

Transition metal dichacogenides (TMD) represent an important class of layered compounds which are gaining lately an enormous interest in electrochemistry. Exfoliation of TMD materials to obtain single to few layer sheets is generally obtained through the intercalation of organolithium compounds. Here we investigated and compared the capacitive behavior of four representative TMD materials, i.e. MoS₂, MoSe₂, WS₂ and WSe₂ exfoliated with different organolithium intercalators, such as methyllithium (Me-Li), n-butyllithium (n-Bu-Li) and tert-butyllithium (t-Bu-Li). We found that both the metal/chalcogen composition and the type of intercalator strongly affect the capacitance of the exfoliated materials. These findings shall have profound implications on the construction of high-performance energy storage devices based on TMD.     

Electrical characterization of LiCo3/5Fe2/5VO4 ceramics

LiCo_3/5Fe_2/5VO₄ has been synthesized by solution-based chemical method. X-ray diffraction study at room temperature reveals an orthorhombic phase of the compound. Electrical properties are studied using complex impedance spectroscopy (CIS) technique in a range of frequency and temperature. The complex impedance plots identify the grain interior, grain boundary and electrode–material interface contributions to electrical response in the material. Temperature dependence of a.c. and d.c. conductivity indicates that electrical conduction in the material is a thermally activated process. The value of activation energy computed from the Arrhenius plot of σ_dc with 10³/T is ～(0.356 ± 0.012) eV (25–275 °C). Frequency dependence of a.c. conductivity at different temperatures is found to obey Jonscher's universal law.     

Collisional de-excitation of the metastableD-states of Ba+ by He,Ne, N2 and H2

The rate constants 〈σ · υ〉 for collisional de-excitation of the metastable 5D states of Ba⁺ ions have been determined in an ion trap experiment. TheD-states are selectively populated by pulsed laser excitation of the 6P _1/2 or 6P _3/2 state and the decay at different background pressures is monitored by the change in fluorescence intensity of the excited ions. From the pressure dependence of the decay constants we calculate the de-excitation rate constants for different collision partners, averaged over the velocity distribution of the trapped ion cloud. For He, Ne, H₂ and N₂ we obtain in the c.m. energy range of 0.1–0.5 eV: 〈σ·υ〉 (He)=3.0±0.2·10^?13cm³/s, 〈σ·υ〉 (Ne)=5.1±0.4·10^?13cm³/s, 〈σ·υ〉 (H₂)=3.7±0.3·10^?11cm³/s, 〈σ·υ〉 (N₂)=4.4±0.3·10^?11cm³/s. The results can be understood qualitatively by a consideration of the ion-atom and ion-molecules interaction potential.     

Carbon monoxide molecules in an argon matrix: empirical evaluation of the Ar·Ar,C·Ar and O·Ar potential parameters

A potential force field has been evaluated for the calculation of the properties of the solid CO-Ar system. The CO·Ar potential energy has been expressed as a sum of the C·Ar and O·Ar interatomic interactions. The (6-exp) Buckingham form of the atom—atom potential, ? = ?Ar^?6 + B exp (?αr), has been used (r is the interatomic distance). The values of the A, B and α numerical parameters for the C·Ar and O·Ar potential have been obtained from those for the C·C, O·O, and Ar·Ar potentials using known combining rules. These values are the following: A_C·Ar = 3379 kJ/mol A⁶, B_C·Ar = 3.12 × 10⁵ kJ/mol, α_C·Ar = 3.493 A^?1, A_O·Ar = 2737 kJ/mol A⁶, B_O·Ar = 3.28 × 10⁵ kJ/mol, α_O·Ar = 3.706 A^?1. The three parameters of the Ar·Ar potential function (A_Ar·Ar = 6554 kJ/mol A⁶, B_Ar·Ar = 3.27 × 10⁵ kJ/mol, α_Ar·Ar = 3.305 A^?1) have been fitted to a set of experimental data for the Ar crystal (zero-temperature lattice spacing and energy, and the value of the isothermal compressibility). The CO·Ar potential surface has been calculated showing the most favourable position of an Ar atom near the CO molecule and the orientational dependence of the CO·Ar interactions. The CO·Ar separation distance at the potential minimum and the depth of the potential well are equal to 3.63 A and ?1.321 kJ/mol, respectively. Comparison has been made of the derived Ar·Ar and Co·Ar potential functions with other such functions available in the literature.     

Gas/gas and gas/wall average energy transfer from very low-pressure pyrolysis

It is shown that data obtained using very low-pressure pyrolysis (VLPP) on the pressure and temperature dependence of unimolecular rate coefficients of reactants with several reaction channels yield average energies transferred in gas/gas and gas/wall collisions (the wall being seasoned quartz at 800–1200 K). The downward average energy transferred, «ΔEå, for chlorocyclobutane/ethylene collisions is found to be 1600 cm^?1 at 970 K; «ΔEå for chlorocyclobutane/wall collisions varies from 5000 cm^?1 (wall efficiency β_w = 0.8) at 930 K to 3500 cm^?1 (β_w = 0.4) at 1150 K; similar values are found from published data on cycloheptatriene and cyclopropane-d₂. This indicates that the assumption of unit wall efficiency usually used in fitting VLPP experiments to RRKM theory needs revision.     

Frequency dependence of intermolecular proton spin-lattice relaxation rate and pair-diffusion constant in neat acetonitrile -d2

Frequency dependence of intermolecular proton spin-lattice relaxation rate [(1/T₁)inter(ω)] in neat acetonitrile-d₂ was studied. From (1/T₁)inter(ω) pair-diffusion constants were determined to be 0.281 × 10^?5 and 0.237 × 10^?5 cm² s^?1 at 22 and ?32.6°C, respectively. These values differ greatly from the self-diffusion constants.     

Charge-transfer transitions in crystalline anthracene and their role in photoconductivity

Electric-field modulated absorption spectra of polycrystalline anthracene layers delineate existence of a series of five charge-transfer bands that can be assigned to transitions within the ab crystal plane. The energy versus distance relationship is coulombic (e = 3.2) yielding an optical band gap E_g^opt = 4.4±0.05 eV. Absorption coefficients are about one order of magnitude lower than calculated by Bounds et al. and indicate a coupling constant A ～ 0.15 for interaction between CT and Frenkel exciton states. Previous data for intrinsic free-carrier production, in particular the energy dependence of the “thermalization” distance, can be consistently interpreted in terms of dissociation of CT pairs if the assumption is made that the vibrational CT energy (0.3 eV) can fully or in part be used for additional separation of the electron-hole pair. The adiabatic (electrical) band gap is E_g^e1 = 4.1±1 eV.