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1. It was established by the method of pulse radiolysis of solutions of naphthalene and anthracene in liquid cyclododecane with optical recording of the intermediate particles formed that cyclododecyl radicals form adducts ArH...R (in the absence of oxygen) and ArH...O2...R (in the presence of oxygen) with naphthalene and anthracene, respectively. 2. The rate constants of the formation of adducts ArH...R, their conversion to more stable particles in first-order reactions, as well as the destruction of the adducts ArH...O2...R in second-order reactions, were determined.

A kinetic study has been made of the attainment and decay of electrical conductivity excited in a polyimide irradiated with fast electron pulses (particle energy 8 MeV, 40 nsec and 2 μsec pulses). It has been found that the delayed component of the radiation induced electrical conductivity consists of fast (τ12=150 nsec) and slow (τ12=2 μsec) components. It is proposed that the fast component is related to a rearrangement of captured charges from shallow to deeper traps, while the slow component is responsible for the experimentally observed inhomogeneous character of the recombination of charge carriers created in the polyimide by irradiation. It is shown that relaxation of induced electrical conductivity after the cessation of irradiation is not a function of the electric field voltage. An estimate of the captured charge drift mobility at room temperature gives μdr=3·6×10−7 cm2/W·sec.

To determine specifics of aromatic polyimides as a new class of polymeric photoconductors, spectroscopic and photoelectric properties of two soluble aromatic polyimides were examined. These polyimides differ in the bridge group in the diimide fragments. The photoconductivity of polyimide films and its spectroscopic distribution, kinetic features of increase and decay of photocurrent were examined with continuous and impulse (third harmonic of a neodymium laser) light, according to light intensity, electric field strength and temperature. Possible mechanisms of forming and transferring charge carriers in polyimides were investigated.

In the field of triarylimidazoles and their derivatives, which are a promising class of organic compounds for the development of photosensitive materials, the authors have investigated the mechanism of photobleaching of 1,4-bis (4,5-diphenyl-2H-imidazol-2-ylidene)-2,5-cyclohexadiene (I) in solution at ca 20 degrees. The biradical form of (I) could not be detected by means of ESR, either with heating or with direct exposure to light in the region of the long-wave absorption band of (I), and the shift of the electronic absorption spectrum of (I) with temperature that is observed is due to a change in the intermolecular interaction of the modecules of (I) with the solvent.

The spectroscopic characteristics and the mechanism of the motion of solvated electrons in polar organic liquids are examined. It is shown that the part of the spectrum where solvated electrons absorb is determined by the polarity of microregions in the liquid. The intensity and half-width of the absorption band depend on the region of the spectrum in which absorption occurs. The theoretical concepts concerning the nature of the solvated electron and the mechanism of its motion are considered. The bibliography includes 65 references.

As a result of experimental investigations of radiation-induced conductivity in foamed dielectrics conducted in air and in vacuum at room temperature using an 8 MeV electron pulse (40 ns) source it is established that two distinctly different conduction mechanisms are responsible for induced conduction in these materials. While a common conduction process prevails in air irradiations (i.e. due to ionization of air leading to formation of free electrons and positive and negative ions) vacuum conductivity is attributed to hot secondary electrons (

Pulse radiolysis methods (50 nsec and 2.5 μs pulse durations) with simultaneous optical and electrical registration have been used in a study of temperature influence on mobility and reactions of the solvated electrons in hexamethylphosphortriamide (HMPA). Transient optical absorption spectra in HMPA were studied. A spectrum of e − solv in pure HMPA was observed up to 2000 nm. Activation energies of e − solv mobility, salt ions mobility (NaBr) and diffusion-controlled reaction between e − solv and induced acceptor (Cu2+) in HMPA were determined (1.6; 5 and 1.8 kcal/mole respectively). The reaction mechanism and migration process of e − solv are discussed on the basis of obtained results.

CONTENTS I. Introduction 736 II. Procedure 737 III. Electrical properties 737 IV. Electron spin resonance 739 V. Influence of impurities on the electrical properties 741 VI. Conduction mechanism 742 VII. Nature of the paramagnetism 744

Pulse radiolysis methods with simultaneous optical and electrical registration have been used in a study of transient charged species in pure hexamethylphosphortriamide (HMPA) and its solutions of alkaline metal salts. A number of transient optical absorption bands were observed, including the solvated electron (es ) spectrum. The experimental technique allowed one to establish some primary reactions in the radiolysis mechanism of HMPA and to determine mobility values of charged species. In case of salt solutions an increase of G(es ) up to the value of total ionization as a result of salt concentration increase (10−3−3:10−1 M) was observed. The possibility of thermalized electron stabilization by cations of alkaline metals is discussed. The concentration dependence of G(es ) is described by an analytical formula if one assumes that es is stabilized by metal cations in the form of a complex [M + …e − 2]. The transient absorption band observed in the near IR is ascribed to this complex. The time o...

Ferrocene in solution does not enter into a donor-acceptor interaction with more than one CBr4 molecule.

1. The absorption spectra and the kinetics of the decolorization of a photochromic film of a copolymer of indolinospiropyran with styrene have been studied in the short-time region. The decolorization mechanism in the film differs significantly from the mechanism in solution, since only the most stable stereoisomers of the colored form are formed owing to the greater viscosity. 2. A correlation has been discovered between the decolorization kinetics and the decay of the nonstationary dark conductivity. It is most likely that the nonstationary conductivity is due to the equilibrium concentration of the charge carriers in the colored film of the copolymer, which is higher than in the original film.

The action of light in the Cu(II) d-d transition region on systems containing polyvinyl alcohol and cupric ions leads to a decrease in the cupric ion concentration and the appearance of a new band. The system returns to the initial state in the dark.

1. Acceptor impurities on the surface of anthracene and in the presurface layer lead to the formation of regions with a high concentration of holes. 2. When an electrochemical reaction, which injects holes into anthracene, proceeds at the phase boundary, the existence of regions on the surface with a high concentration of holes leads to a pitting character of the corrosion, which indicates its autocatalytic character. 3. In the case where anthracene, excited by the pulses of low-energy electrons, exhibits a nonequilibrium conductivity, the existence of regions with a high concentration of holes is manifested in the appearance of the slow component of the hole conductivity and an increase in the efficiency of generating current carriers in the surface layer.

A large number of investigations has been devoted to the mechanism of conduction in organic semiconductors.The first step in the study of the mechanism of conduction is generally the determination of n and µ appearing in the expression for conductivity σ = enµ. In inorganic semiconductors, this is done by measuring the Hall effect. Then, by studying the dependence of µ and n on the temperature and other parameters, the mechanism of conduction in the material investigated is deduced.

At the present time, hundreds of new organic semiconducting materials have been obtained [1–3]. In this chapter we shall consider those characteristics of these materials that can be used in various branches of power engineering and radioelectronics [4].

A study has been made of the spectral characteristics and photoelectric sensitivity of many organic polymers with conjugated double bonds. In spite of the considerable number of papers devoted to photoelectric sensitivity, so far there has been no sufficiently well-founded theory of the mechanism of the photoexcitation of the current carriers and their transfer in the polymeric structure. Nevertheless, the characteristics of the photoconductivity of several polymers with conjugated bonds give grounds for considering these polymers as promising materials for practical use.

The question of the possibility of applying to biopolymers the ideas developed in the physics of the solid state has a fairly long history. In 1938 Jordan [1] and in 1941 Szent-Gyorgyi [2] suggested that proteins may possess the nature of semiconductors. Subsequent biophysical investigations of biopolymers at the molecular level led to the conviction that the phenomena taking place in ordered biological structures cannot be interpreted unless in some cases the biopolymer is considered as a solid body. This is explained, in the first place, by the fact that proteins consist of very large molecules with molecular weights reckoned in millions and, in the second place, by the fact that the enormous role played by the medium (for example, a solvent) in which the various processes take place is becoming ever clearer to chemists and biologists.

At the present time, numerous polymers have been synthesized which are stable at high temperatures and possess very diverse electrical and magnetic properties. Their catalytic activity in heterogeneous catalysis has been studied for the cases of the decomposition of hydrogen peroxide [1] and formic acid [2, 3], de-hydrogenation and dehydration reactions [3, 5, 6], and the decomposition of hydrazine and nitric oxide [6, 8].

There is no doubt that the surface properties of organic semiconductors are extremely important both for understanding the processes taking place at the boundary of separation of two phases and for more complete understanding of the processes taking place in the bulk of the semiconductor. The influence of the state of the surface and the processes taking place at the surface on the bulk properties is particularly strong when the semiconductors have a low intrinsic conductivity [1]. In the adsorption of gases on the surface of a semiconductor it has been found experimentally that some molecules are capable of increasing the concentration of electrons in the surface layer and others of decreasing it. The process of adsorption may be considered in two ways: either as a creation of donor (acceptor) impurities at the surface [2, 3] or as the formation of charge-transfer complexes [4].

One of the most important problems of present-day chemistry is the creation of new substances and materials possessing a series of valuable properties. Particularly great prospects have been opened up in the synthesis and study of organic compounds possessing delocalized electrons because of the presence in them of conjugated bonds or the formation of charge-transfer complexes. Such compounds have acquired the name of organic semiconductors. Starting in 1960, the volume of investigations on the chemistry and physics of these materials has risen to such an extent that the possibility has appeared of generalizing some basic achievements in this field [1, 2]. At the present time organic semiconductors include both low-molecular-weight compounds and polymers with a large number of conjugated bonds, charge-transfer complexes in which, owing to a definite structure, conditions are created for the delocalization of an electron, stable free radicals, and also some biopolymers (including proteins) the conductivity of which can be explained by a nonionic mechanism.

A template oxidative polymerization of aniline in aqueous solutions containing poly-(2-acrylamido-2-methyl-1-propanesulfonic acid) and ammonium persulfate yields a polyaniline complex with the polyacid soluble in water. According to the data of spectral measurements, the process of polymerization is of a pronounced autocatalytic nature. The consequences of this are both the formation of a nonuniform distribution of oxidized and nonoxidized fragments of the polymer chain and the formation of a macroscopic scale of redox nonuniformities in the reaction volume during the process of polymerization. The spectra of absorption of the polyaniline/polyacid films on transparent glass electrodes with a conductive layer of SnO2 and the data of potentiodynamic measurements in the potential region 0–1.0 V (Ag/AgCl) are typical for polyaniline with moderate electroconduction.

Various aspects of the kinetics of the radiation-induced conductivity in polymers, i.e. build-up and decay curves, non-linear dose rate effects, approach to the steady state are investigated by means of approximate analytical solutions as well as computer simulation for the case of exponential trap distribution (computer calculations are performed specifically for the case of dispersion parameter α = 0.5). The widest possible range of irradiation conditions is covered (pulse length 1 ns, 100 μs, 10 ps, 0.1 ms including the steady state; dose per pulse from zero to 105 Gy). The problem of the best choice of normalization parameters is also briefly discussed. Verschiedene Aspekte der Kinetik der strahlungsinduzierten Leitfahigkeit in Polymeren, d. h. die An-und Abklingkurven, nichtlineare Dosisrateneffekte, das Erreichen des stationaren Zustands, werden sowohl mittels analytischer Naherungslosungen als auch mit Computersimulation fur den Fall einer exponentiellen Haftstellenverteilung untersucht (die Computerberechnungen speziell fur einen Dispersionsparameter α = 0,5). Der weitestmogliche Bereich von Strahlungsbedingungen wird uberdeckt (Impulslange 1 ns, 100 ns, 10 ps, 0,1 ms einschlieslich des stationaren Zustands; Dosis pro Impuls reicht von Null bis 105 Gy). Das Problem der besten Wahl der Normierungs-parameter wird kurz diskutiert.

Radiation induced conductivity of PET and PS is investigated under pulse irradiation conditions in vacuum at room temperature. Main emphasis in these studies is laid on the pulse length, dose per pulse, and accumulated dose dependence of the induced conductivity. The observed sublinear dependence of induced conductivity on dose rate at high dose per pulse experiments is shown to arise by a trap-controlled bulk recombination and is well accounted for in terms of the conventional Rose-Fowler formalism. This same model is quite successful in interpretation of the accumulated dose effects. Die strahlungsinduzierte Leitfahigkeit von PET und PS wird unter Impulsbestrahlung im Vakuum bei Zimmertemperatur untersucht, wobei hauptsachlich die Abhangigkeit der induzlerten Leitfahigkeit von der Impulslange, Dosis pro Impuls und akkumulierter Dosis betrachtet wird. Es wird gezeigt, das die beobachtete sublineare Abhangigkeit der induzierten Leitfahigkeit von der Dosisrate bei hohen Dosen pro Impuls durch einen Haftstellen-gesteuerten Volumenrekombina-tionsmechanismus hervorgerufen wird und mit dem konventionellen Rose-Fowler-Formalismus gut erklart werden kann. Dasselbe Modell ist aueh erfolgreich bei der Interpretation des Einflusses der akkumulierten Dosis.

By using formal estimation methods, it is shown that heterogeneous redox structures, which are formed in the course of oxidation of vacuum evaporated thin polyaniline layers in the temperature range of 0–30°C, become more ordered with the increase in the oxidation temperature.

Cyanine dye electroluminescence was observed in single layer light-emitting diodes based on electron-hole conducting polymers. The appearance of light emission in the visible range depended on the reduction/oxidation potentials of the dyes used. In polymer systems, the electroluminescence of cyanine dye J-aggregate nanocrystalline phase was detected for the first time. J-aggregate/polymer composites exhibiting intense absorption band with a maximum in the red range were developed on the base of polyimides and a copolymer coformed from phenylacetylene and 4-methylcoumarin-4-pentynoate doped with the dye luminophores. Efficient electrolumunescence was revealed in these systems. It was demonstrated that J- aggregates play an active role in charge carrier transport in the composite materials. In particular, anthracene-containing polyimides exhibiting electron-hole transport appeared to be appropriate media for the generation of J-aggregate electroluminescence.

Pyrazolo[3,4-b]quinoline derivatives are found to have electron transport properties. A field dependent electron drift mobility, in the range of 10−6–3×10−5 cm2/(V s) at an electric field of (1–7)×105 V/cm, has been found from the pyrazolo[3,4-b]quinoline doped polystyrene specimen, which was measured using a conventional time-of-flight method. The results are fit well into a correlated disorder model for a dipole medium when energetic features of the transport molecules are also taken into account.

Build-up and decay of radiation-induced conductivity associated with the motion of free charge carriers in the presence of multiple trapping is treated theoretically for both, exponential and uniform trap distributions. Approximate analytical solutions describing its growth and decay are presented. These model considerations are shown to agree well with available experimental data. Aufbau und Abklingen der strahlungsinduzierten Leitfahigkeit, die mit der Bewegung von freien Ladungstragern unter Wirkung von Mehrfachtrapping verknupft sind, werden theoretisch fur eine exponentielle sowie fur eine gleichformige Trap-Verteilung untersucht. Analytische Naherungslosungen werden angegeben, die Wachstum und Abklingen beschreiben. Es wird gezeigt, das diese Modellbetrachtungen gut mit vorhandenen experimentellen Werten ubereinstimmen.

The theory of the temperature shift in the absorption spectrum of a solvated electron is discussed. The theory is based on the concept of the interaction of an electron bound in a zero-range potential with long-wavelength classical vibrations of the medium. The theory is compared with data for the absorption spectra of e–s in methyl alcohol measured over a wide range of temperatures. Satisfactory quantitative agreement has been found.