Poster communications 46-90

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PC46

Optical and Dielectric Properties of New Diazobenzene Copolyethers Embedded in Polymer Matrices

M. Strat¹, Georgeta Strat², V. Scutaru³, S. Gurlui¹ and Irinel Grecu²

¹Department of Optics and Spectroscopy, ”Al.I. Cuza”, University of Iasi,

²Department of Physics, ”Gh. Asachi” Tehnical University of Iaşi, Romania

³Department of Electricity and Magnetism ”Al. I. Cuza” University, Romania

E-mail: mstrat@uaic.ro

In a series of previous works, the synthesis of some polyethers by phase transfer catalysis technique was presented . These polymers were obtained by a polycondensation reaction between 3, 3-bis (chloromethyl) oxetane ( BCMO) and various bisphenols, some of them evidencing a liquid crystalline ( LC) behavior .

The presence of the azobenzene units in the polymers’ structure confers on them important properties with practical applications in optics and optoelectronics.

If anisotropic foils are made of such a polymer, then the molecules of a nematic liquid crystal, which need not contain azobenzene units, that are in contact with the foil can be aligned by means of a process of photoisomerization of the diazobenzene units when linearly polarized Ar⁺ laser light is shown on the foil .

It is considered that the orientation of the liquid crystal molecules by the azobenzene units is mainly the result of specific molecular interactions between the photochromic units from the polymer layer and the liquid crystal molecules. These specific interactions depend on both the structure of the liquid crystal molecules and the area occupied by the azo units in the polymer surface layer.

In this work, the copolyethers, which contain diazobenzene groups in their molecular structure, are studied and, unlike the other situations, the azogroups are fixed within the polymeric chain.

Because the copolymer is a thermotropic LC with thermal transitions situated around 210 ⁰C, it is impossible to study the photoisomerism in the LC state * the cis-trans transitions is thermally activated). As a consequence, the copolymer was incorporated into a matrix foil. Thus the photochromic behavior can be studied at room temperature. Therefore, the obtaining of potential surface command by modification of the polymer matrix and diazobenzene concentration could be expected.

Reference.

N.Hurduc, V.Bulacovschi, D.Scutaru, V.Barboiu and C.I.Simionescu - Eur.Polym.J.,29, p.1333, (1993).

PC47

Cancelled, abstract not supplied

PC48

Non-dispersive Hole Transport in a 9,9-spirodifluorene

Dmitry Poplavskyy^a, Jenny Nelson^a

^a EXSS Group, Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2BZ, United Kingdom

Small molecules of Spiro-linked compounds, in particular 2,2’,7,7’-tetrakis-(N,N’-di-4-methoxyphenylamino)-9,9’-spirobifluorene (Spiro-OMeTAD), have proven to be very good and stable hole transporting materials in application to organic LEDs [1] and especially to solid-state dye-sensitized solar cells (SS-DSSC) [2]. However, despite the recent progress [3] in improving efficiency in SS-DSSC based on Spiro-OMeTAD, the basic hole transport properties, in particular the hole mobility, of this material remained unknown.

Here we present the result of studies of the hole transport in this material by three independent techniques: steady-state current-voltage (IV) characteristics, time-of-flight (ToF) transient method and dark-injection (DI) transient current method. It was found that PEDOT:PSS and oxygen-plasma-treated ITO both provide ohmic contacts to the material, as proven by observation of space-charge-limited DI current transient with a characteristic maximum. We also observed non-dispersive ToF transients that easily allowed to determine the mobility. The DI technique was applied in relatively thin samples (d < 1 m m) while the ToF method was used to measure mobilities in thick samples (d > 1 m m). Excellent agreement between the mobilities determined from the DI results and from the ToF results was observed for a wide range of thicknesses. No noticeable thickness-dependence of the mobility was observed in the thickness range from 0.16 m m to 4 m m.

The hole mobility followed Poole-Frenkel-like field dependence reaching the value of ~10^-4 cm²/Vs at an electric field of 10⁵ V/cm.

Also, excellent agreement was observed between the measured steady-state currents and those calculated from the measured transient (DI and ToF) mobilities using the Mott-Gurney expression.

[1] J. Salbeck et al, Synth. Met. 91, 209 (1997).

[2] U. Bach et al, Nature 395, 583 (1998).

[3] J. Krüger, R. Plass, Le Cevey, M. Piccirelli, M. Grätzel, APL 79, 2085 (2001).

PC49

DISPERSIVE AND NON-DISPERSIVE HOLE TRANSPORT IN POLYFLUORENE-ARYLAMINE COPOLYMERS

Dmitry Poplavskyy^a, Jenny Nelson^a, Donal D. C. Bradley^a

^a EXSS Group, Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2BZ, United Kingdom

Poly(9,9-dioctylfluorene) (PFO) and its copolymers are considered to be some of the most promising materials for use in polymeric light-emitting diodes (PLEDs). Recently a new family of PFO copolymers, dioctylfluorene-triarylamine conjugated polymers, was developed [1]. These materials, that show high hole mobilities reaching 10^-3 cm²/Vs combined with low ionisation potentials (~ 5.0-5.3 eV), have a good potential for application in PLEDs.

Here we present a comparative study of two representative polymers, poly(9,9-dioctylfluorene-co-bis-N,N’-(4-butylphenyl)-bis-N,N’-phenyl-1,4-phenylenediamine (PFB) and poly(9,9-dioctylfluorene-co-bis-N,N’-(4-butylphenyl)-bis-N,N’-phenylbenzidine (BFB), that exhibit non-dispersive and dispersive time-of-flight mobilities, respectively. A detailed study of the hole mobility in a wide range of spin-cast film thicknesses and applied electric fields is done by means of dark-injection space-charge limited transient currents. The results obtained by this method are also compared to the time-of-flight and steady-state current-voltage measurements. Mobilities are studied in samples as thin as 200 nm allowing to relate measured mobilities to those realised in real devices that usually have similar thicknesses. Effects of dispersion in hole transport are discussed by analysing the mobilities of the two materials, BFB and PFB, at different sample thicknesses.

[1] M. Redecker, D. D. C. Bradley, M. Inbasekaran, W. W. Wu, E. P. Woo, Adv. Mater. 11, 241 (1999).

PC50

Studies of host-guest thin films of corona-poled betaine-type polar molecules by Kelvin probe technique and atomic force microscopy

R. DOBULANS^a, D. Cepite^a, E. FONAVS^a, I. MUZIKANTE^a, A. TOKMAKOV^a, D. ERTS^b, B. POLAKOV^b

^aInstitute of Physical Energetics, Academy of Sciences of Latvia, Aizkraukles Str. 21, LV-1006 Riga, Latvia

^bInstitute of Chemical Physics, University of Latvia, Raina Blvd. 19, Riga LV-1586, Latvia

Organic dye-doped materials have received considerable attention because of their large dipole moments and optical nonlinearities. Amorphous dipole electrets for photonic applications contain chromophore dipoles, which consist of acceptor and donor groups linked by a bridge of delocalized -electron system. Non-linear and electret properties are obtained by dipole orientation of active units.

In this work betaine-type (IPB) molecule was investigated. As a result of the asymmetry of charge distribution, molecules posses in the ground state a considerable permanent dipole moment.

In our experiments, host-guest systems were chosen. Optically transparent polymer poly(methylmethacrylate) (PMMA) was used as host. The different solvents were used to deposit casted host-guest films onto gold and ITO electrodes. The high-electric field corona poling was used to generate dipole orientation of dye molecules in polymer matrices. The topography of the film surface was obtained by atomic force microscopy. In order to investigate the changes of the surface structure the samples were easured as-prepared, after corona poling and after thermal treatment as well.

IPB/PMMA films exhibited very smooth surface over range 1x1m. The evaluated roughness S_q was of 0.5-0.6nm. Some pinholes in as-prepared films were observed.

The value of the surface potential of host-guest films after poling increased from some mV to ~ -3.2V. The surface of the polymer films drastically changed and the roughness of the surface increased. After heating over the glass transition temperature the surface potential decreased close to as-prepared sample with randomly distributed polar molecules. The surface of the polymer films became more smooth again. The thermally stimulated surface potential dependences on poling temperature were investigated. The - and -relaxation processes of PMMA polymer influenced the value of the surface potential of the film.

PC51

GENERATION OF THE CHARGE CARRIERS PAIRS IN TETRACENE LAYERS

M. OBAROWSKA*, R. SIGNERSKI, J. GODLEWSKI

Department of Physics of Electronic Phenomena, Gdansk University of Technology, Narutowicza 11/12, 80-952 Gdansk, Poland,

^*e-mail: mabo@mif.pg.gda.pl

The photocurrent of both signs of single tetracene layers in a sandwich type arrangement with aluminum electrodes was studied as a function of excitation wavelength in the short wavelength region.

A different current dependence is observed between positive and negative charge carriers for various applied voltages. The positive photocurrent (j⁺) increases more rapidly with applied voltage than in the negative case (j^-). The values of j^- photocurrent are much smaller then those for j⁺. The relationship between the current density and the light intensity may be expressed by the formula: , where the power n is estimated from measurements to be in the range 0.5 to 1 for j^- and close to 1 for j⁺. This result for negative photocurrent indicates a disagreement with the predictions of the Onsager model for the charge carrier photogeneration mechanism [1]. According to this model, the photocurrent should depend linearly on the light intensity (n=1). The results also indicate that the recombination between holes and electrons does not fully control the electron production mechanism, as n would be smaller or equal to 0.5.

Based on these experimental results, it is concluded that there are different mechanisms responsible for hole and electron production in tetracene layers. The main process for positive-charge production is the ionization within the bulk. For negative photocurrent, not only the bulk generation can play an important role but also deep surface trapping and detrapping processes. The conclusions resulting from experimental measurements are complemented by a theoretical description, derived by us, based on the set of equations including the continuity and the Poisson formulas for steady state conditions.

References:

1. M. Pope, C. E. Swenberg, Electronic Processes in Organic Crystals and Polymers, New York, Oxford University Press, 1999.

PC52

ELECTRICAL PROPERTIES OF CONDUCTIVE COMPOSITES POLYETHYLENE / MODIFIED CARBON BLACK

S. PODHRADSKÁ^a, M. OMASTOVÁ^a, J. PROKEŠ^b, J. STEJSKAL^c

^a Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9,

SK-842 36 Bratislava, Slovak Republic

^b Charles University Prague, Faculty of Mathematics and Physics, Ke Karlovu 5,

CZ-121 16 Prague 2, Czech Republic

^c Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, CZ-162 06 Prague 6, Czech Republic

An addition of a conducting filler, such as metals particles, carbon black, short carbon fibres or graphite into conventional polymers enables the preparation of new materials with unique electrical properties. Carbon black has been widely used as a filler in various polymer matrices, e.g., polyolefins¹, rubbers², and others. The electrical and mechanical properties of composites are affected significantly by the way of composite preparation. Carbon black (CB) filled polymers are very attractive because of their numerous applications in industry. Nevertheless, all applications of conducting polymer composites depend on the stability of material properties.

The stability of electrical and mechanical properties of polymer composites, polyethylene (PE) filled with CB and with surface-modified CB by polypyrrole (PPy)³ or polyaniline (PANI), was investigated during slow heating-cooling cycling. A significant increase of conductivity was found in composites during the temperature cycling below the melting point of PE (T_m = 109°C). This effect can be explained by the re-crystallization processes in the non-conductive PE matrix during slow cooling. Crystallinity increase leads to the increased concentration of conductive filler in amorphous PE phase. The thermally treated composites showed the decrease of elongation at break and increase of the Young modulus. The modification of CB by conductive polymers influences thermal stability of composites. The conductivity of the composites containing modified CB increased also during the heating-cooling cycles above T_m of PE while the conductivity of PE composites containing pure CB rapidly decreased.

1. Z. S. Petrovic, B. Martinovic, V. Divjakovic, J. Budinski-Simendic, J. Appl. Polym. Sci. 49, 1659 (1993).
2. L. Slusarski, M. Zaborski, J. B. Donnet, Angew. Makromol. Chem. 222, 49 (1994).
3. M. Omastová, J. Prokeš, S. Podhradská, I. Chodák, Macromol. Symp. 170, 231 (2001).

Acknowledgement. The research was supported by the Grant Agency for Science of the Slovak Academy of Sciences (GAV-2/1060/21).

PC53

INFLUENCE OF SURFACTANTS ON PROPERTIES OF CHEMICALLY PREPARED POLYPYRROLE

M. OMASTOVÁ^a, M. TRCHOVÁ^b, J. PROKEŠ^b, J. KOVÁŘOVÁ^c

^a Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9,

842 36 Bratislava, Slovak Republic, e-mail: upolmaom@savba.sk

^b Charles University Prague, Faculty of Mathematics and Physics, V Holešovičkách 2, 180 00 Prague 8, Czech Republic

^c Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic

Polypyrrole (PPy) is one of the representatives of conducting polymers because of its good electrical conductivity, environmental stability and relative ease of synthesis. PPy can be prepared by electrochemical or chemical oxidation of pyrrole in various organic solvents and in aqueous media. In a chemical oxidative polymerization, many oxidizing agents have been used, i.e. ferric chloride or sulfate, ammonium peroxydisulfate, and ferric perchlorate being typical examples. The preparation conditions and the presence of various additives influence the properties of the final conducting polymer.

The effect of various surfactants introduced during the synthesis of PPy was investigated. PPy was prepared chemically using an oxidant Fe₂(SO₄)₃ and anionic, cationic or non-ionic surfactant. Elemental analysis and IR spectroscopy indicate that anionic surfactant, unlike the other types, is incorporated into PPy structure, similarly like the anion of an oxidant. The conductivity increase by 1–2 orders of magnitude was registered for PPy-containing anionic surfactant, compared to the PPy prepared with other surfactant types or without surfactants. The most stable behaviour and the smallest decrease in electrical conductivity during a heating–cooling cycling was observed for PPy prepared in the presence of sodium dodecylbenzenesulfonate. Thermal stability of PPy samples was investigated by thermogravimetrical analysis. The results showed that PPy prepared in the presence of anionic surfactant are much more stable compared with other PPy samples. While PPy prepared in the absence of surfactant or with a cationic or non-ionic surfactants is hygroscopic and looses about 7 wt % of mass during heating to 100°C, PPy containing an anionic surfactant is stable up to 300°C. The presence of anionic surfactant during chemical synthesis influences PPy morphology as demonstrated by scanning electron microscopy.

Acknowledgement. The research was supported by the Grant Agency for Science of the Slovak Academy of Sciences (GAV-2/1060/21).

PC54

MEASUREMENTS OF CHARGE CARRIERS MOBILITY USING PS. LASER IN HPLCP PANEL

J. MYSLIWIEC^a, S. BARTKIEWICZ^a, A. MINIEWICZ^a, B. SAHRAOUI^b, F. KAJZAR^c

^aInstitute of Physical and Theoretical Chemistry, Wroclaw University of Technology, 50 – 370 Wroclaw, Poland

^bUniversité d‘Angers, Laboratoire POMA CNRS UMR 6136 2, Bd Lavoisier 49045 Angers, France

^cCEA – LIST (Recherche Technologique), DECS/SE2M/LCO, CEA Saclay, 91191 Gif sur Yvette Cedex, France

We present studies of the photorefractive properties of hybrid: polymer – nematic liquid crystal panels (HPLCP) equipped with either one or two photconducting layers under short pulse (20 ps) laser illumination. Using a two – wave mixing technique with cw He – Ne laser we monitored the temporal evolution of intensity of the first – order diffraction after the pulse excitation. Knowledge of refractive index grating formation in HPLC and erasure dynamics under the ps laser shot, allows for evaluation of charge carrier mobilities (holes and electrons) in the photoconducting polymer layers. We analysed three different polymers such as poly (N-vinyl carbazole) doped with trinitrofluorenone molecules, and two copolymers: polybuthylthiophene with Disperse Red 1 and polydecylthiophene with Disperse Red 1.

Fig.1. Temporal response of light diffraction on index grating after the ps laser pulse excitation measured in function of tilt angle a . LC panel has two photoconducting electrodes (polybuthylthiophene + DR1). The two time constants t ₁and t ₂ were used to the charge carrier mobility evaluation.

PC55

PHOTOALIGNING PROPRIETIES AND SOLVATOCHROMIC BEHAVIOUR OF AZOBENZENE DERIVATIVE DISPERSE ORANGE 3

K. MATCZYSZYN¹, S. BARTKIEWICZ¹, J. MYSLIWIEC¹, O. YAROSHCHUK²

¹Institute of Physical and Theoretical Chemistry, Technical University of Wroclaw, Wyb.Wyspianskiego 27, 50-370 Wroclaw Poland matczyszyn@kchf.ch.pwr.wroc.pl

²Institute of Physics, NASU, prospect Nauki 46, 03028 Kyiv, Ukraine

Azobenzenes have recently attracted increasing attention due to their emerging applications in photonics. The molecules are characterised by a high photoinduced anisotropy (the photoinduced birefringence can be as high as 0.3 [1]), being excellent photoaligning substrates for liquid crystals (LC) [2] and highly efficient photorefractive media [3].

The solvatochromic behaviour of the 4-nitro-4’-aminoazobenzene (Disperse Orange 3, hereafter referred to as DO3) was studied in orger to select a solvent of an appropriate polarity for further experiments. The LC photoaligning properties and photochromism of azopolymers were associated to build and examine a novel photoactive system.

Cells were prepared, consisting of layers of polyamic acid – DO3 blend spin coated on conducting glass slides. The command surfaces prepared in such a way were irradiated with polarized UV light in order to generate LC easy axis in the direction parallel to the direction of rubbing. The cells were then filled with several types of nematic LC. A degenerate two wave mixing system based on He-Ne laser (P=25mW, l =632.8 nm) was realised. The dependencies of the diffraction efficiency on the incidence angle of the recording beams, grating period, applied voltage, as well as the dynamic characteristics of the gratings have been investigated. Periodic light dispersion causes the change of the orientation of the photochromic molecules in the polymer film. The placement of the azomolecules influences the position of the LC molecules near the surface and due to the elastic forces it is mapped on the LC volume in the sample.

1. O. Yaroshchuk, T. Sergan, J. Lindau, S.N. Lee, J. Kelly, L.-C. Chien, J.Chem.Phys., 2001,114, 5330.
2. W.Gibbons, P.Shannon, S.Shao-Tang, B.Swetlin, Nature, 1991, 351, 49.
3. S.Bartkiewicz, K.Matczyszyn, A.Miniewicz, F.Kajzar, Opt.Comm., 2001, 187, 257.

PC56

PROPERTIES OF OPTICALLY ADDRESSED LIQUID CRYSTAL SPATIAL LIGHT MODULATORS STUDIED BY MACH-ZEHNDER INTERFEROMETRY

KATARZYNA KOMOROWSKA, ANDRZEJ MINIEWICZ, JANUSZ PARKA*,

Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland

*Institute of Technical Physics, Military University of Technology, 00-908 Warszawa, Poland

It is well known that liquid crystal materials are attractive for many optical devices because of their high optical birefringence n= n_e - n_o Electrically addressed liquid crystal spatial light modulators (EA LC SLM) are widely used in modern optics [1]. These LC matrix displays have a discrete, well-defined, pixel structure, which limits optical resolution, because of diffraction of coherent beam on pixels [2]. Optically addressed liquid crystal spatial light modulators (OA LC SLM) were proposed in order to overcome these disadvantages [3]. OA SLM can be used as the self-adjusting nonlinear optical filter in which phase shift is a function of an externally applied voltage and an intensity of addressing light [4].

In this work we present the preliminary results of light-induced phase shifts in OA LC SLM observed in Mach-Zehnder interferometer. Experiments were performed in the panels filled with smectic and nematic liquid crystals. Optical addressing was realised by Ar⁺ laser beam at =514.5 nm. Reading beam was supplied from He-Ne laser (632.8 nm). Operation voltage for studied panels was in the range 4-20V. The general results achieved for panels: total phase shift under influence of addressing light: 1 - 6 , sensitivity to the addressing light (~W/cm² per 2 phase change), speed of response to the light (10 ms-30s), recovery time (0.5-120 s).

[1] J. Zmija, S.J. Klosowicz, J. Kedzierski, E. Nowinowski - Kruszelnicki, J. Zielinski, Z. Raszewski, A. Walczak, J. Parka, Optoelectron. Rev., 5 (1997) 93.

[2] G. Moddel, in: U.Efron (Ed.), Spatial Light Modulator Technology: Materials, Devices and Applications, Chap.6, Marcel Dekker, New York, (1994), 287.

[3] K. Komorowska, A. Miniewicz, J. Parka, Synthetic Metals, 109 (2000) 189.

[4] G. W. Carhart, M.A. Vorontsov and E.W. Justh, “ Opto-electronic Zernike filter for high-resolution wavefront analysis using a phase-only liquid crystal spatial light modulator”, Proc. SPIE, 4124 (2000) 138.

PC57

HOW USEFUL IS DSC TECHNIQUE IN STUDIES OF SOLID STATE REACTIONS IN PHOTOCHROMIC MATERIALS

E. ŚLIWIŃSKA, J. SWORAKOWSKI

Institute of Physical and Theoretical Chemistry, Wrocław University of Technology, Wybrzeże S. Wyspiańskiego 27, PL-50370 Wrocław, Poland

Differential Scanning Calorimetry (DSC) was employed to study the kinetics of reverse thermally driven reactions in polycrystalline samples of three photochromic compounds. Results obtained on two dihydropyridine derivatives (DHP and BDH) [1] were critically re-examined and compared with results of the experiments performed with an acridizinium salt (AS) [2]. Heat flow curves, measured on samples previously irradiated with UV, exhibited broad exothermic anomalies at elevated temperatures (above ca. 320 K for dihydropyridines and ca. 490 K for AS), observed only once after irradiation and attributed to bleaching reactions. Our results provide information about the enthalpy of the bleaching process and demonstrate that the thermal behaviour of the samples depends on conditions of preparation of the samples and of irradiation. The activation energies of bleaching reactions, determined from fractional heating experiments [3], amount to ca. 130 ± 30 kJ/mol (DHP and BDH) and to ca. 110 ± 10 kJ/mol (AS). Exact determination of the distribution of activation energies proved difficult due to uncertainties with a proper setting of baselines.

Experiments were carried out using equipment purchased by the Foundation for Polish Science and by the Centre of Advanced Materials and Nanotechnology of Wroclaw University of Technology. The work has been partly supported by the Polish State Committee for Scientific Research (grant No 3T09A 106 19).

[1] J. Sworakowski, S. Nešpůrek, J. Lipiński, E. Śliwińska, A. Lewanowicz, A. Olszowski, in: F. Kajzar and V.M. Agranovich (Eds.), Multiphoton and Light Driven Multielectron Processes in Organics: New Phenomena, Materials and Applications, pp.249-260, Kluwer Acad. Publ. Dordrecht, 2000.

[2] H. Ihmels, D. Leusser, M. Pfeiffer, D. Stalke, J. Org. Chem., 64(1999)5715.

[3] J. Sworakowski, S. Nešpůrek, Chem. Phys. 238(1998)343.

PC58

POLARIZED ELECTROLUMINESCENCE FROM BILAYER STRUCTURES

G. WANG^a, S. NEŠPÙREK^a, J. RAKUŠAN^b, M. KARÁSKOVÁ^b

^aInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic

^bResearch Institute of Organic Syntheses, 53218 Pardubice-Rybitví, Czech Republic

Poly[methyl(phenyl)silylene] (PMPSi) with significant electron delocalization along the chain and therefore with an effective charge carrier transport [1] shows an angular-dependent photoinduced cleavage of the Si-Si bonds, formation of polysiloxane structures and quasi-stable photogenerated ion-pairs preferentially within segments oriented along the light polarization [2]. These effects make it possible to use PMPSi as a hole-
-transporting structure for the preparation of oriented organic films. A PMPSi layer, 120 nm thick, was prepared by spin coating on ITO glass and, after drying, irradiated with linearly polarized UV light. Then water-soluble hydroxyaluminium phthalocyaninedisulfonate [Al(OH)Pc(SO₃Na)₂] was deposited by spin coating on PMPSi and on the top Al electrode was deposited. The cell showed a current-voltage characteristic typical of space-charge-limited (SCL) current with typical trap-filled-limit and trap-free regions (Fig. 1). For the applied voltages higher than 10 V, i.e. for the trap-free SCL current, a polarized electroluminescence (EL) was observed. Its spectral characteristic consisted of two peaks with maxima at about 320 and 700 nm (Fig. 2); their polarized anisotropies R_EL= F ï ê / F ^ are ca. 15 and 0.5, respectively.

[1] S. Nešpůrek, A. Eckhardt, Polym. Adv.Technol. 12, 427 (2001).

[2] A. Dyadyusha, S. Nešpůrek, Yu. Reznikov, A. Kadashchuk, J. Stumpe, B. Sapich, Mol. Cryst. Liq. Cryst. 359, 67 (2001).

PC59

FTIR SPECTROSCOPY OF THE PROTONATION OF POLYANILINE WITH AN EXPLOSIVE

M. TRCHOVÁ^a, I. SAPURINA^b, J. PROKEŠ^a, J. STEJSKAL^c

^aFaculty of Mathematics and Physics, Charles University Prague, V Holešo-vičkách 2, CZ-180 00 Praha 8, Czech Republic

^bInstitute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg 199004, Russia

^cInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-162 06 Praha 6, Czech Republic

The preparation of materials combining the features of conducting polymers and energetic compounds is demonstrated. The FTIR spectra are used to discuss changes in the molecular structure of product of protonation reaction between two non-conducting compounds, polyaniline (PANI) base and an explosive, 3-nitro-1,2,4-triazol-5-one (NTO). Three ways of preparation have been tested: the interaction of PANI base with NTO dissolved in water, the polymerization of aniline in the aqueous medium containing NTO, and solid-state blending of both components.

The reaction of non-conducting blue PANI base with an acid generally leads to a conducting green protonated PANI. It is thus expected that NTO forms a ”salt” also with PANI base (Scheme 1). From keto-enol tautomeric forms of NTO, the enol form is found in PANI protonated with NTO. The progress of protonation of PANI with NTO was assessed by the increase in conductivity.

Scheme 1. Polyaniline protonated with NTO.

Acknowledgement. The research was supported by the Grant Agency of the Czech Republic (202/02/0698).

PC60

POLYANILINE NANOFILMS PRODUCED BY SURFACE POLYMERIZATION OF ANILINE

S. FEDOROVA^a, I. SAPURINA^a, J. STEJSKAL^b

^aInstitute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg 199004, Russia

^bInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-162 06 Praha 6, Czech Republic

Polyaniline (PANI) is a typical representative of conducting polymers. It is prepared by the oxidation of aniline, e.g. with ammonium peroxydisulfate, in the aqueous acidic medium [1]. Any surface in contact with the reaction mixture becomes coated with a thin PANI film during the polymerization of aniline [2]. The typical film thickness on glass is ca 100–200 nm. The PANI chains are oriented preferentially perpendicularly to the surface producing morphology close to polymer brushes [3].

Polyaniline hydrochloride (PANI)

The polymerization at the surface, producing a PANI film, precedes the polymerization in the bulk, giving rise to a PANI precipitate. This is explained by the heterogeneous catalysis of chain initiation afforded by the surface. The catalytic effect of the surface is illustrated by the acceleration of PANI formation by the introduction of inert silica gel into reaction mixture [4]. Silica gel particles become coated with PANI. An overlayer of conducting polymer can similarly be deposited on various materials (polymers, polymer membranes, noble metals, glass, carbon, silicon, etc.). Inorganic microparticles, polymer microspheres and fibers are encapsulated in conducting polymer by this method.

Acknowledgment. The authors wish to thank the Academy of Sciences of the Czech Republic for financial support (K 4050111).

[1] J. Stejskal, P.Kratochvíl, A.D. Jenkins, Polymer 37, 367–368 (1996).

[2] J. Stejskal, I. Sapurina, J. Prokeš, J. Zemek, Synth. Met. 105, 195–202 (1999).

[3] I. Sapurina, A. Riede, J. Stejskal, Synth. Met. 123, 503–507 (2001).

[4] S. Fedorova, J. Stejskal, Langmuir, submitted.

PC61

TEMPERATURE AND HUMIDITY RELATED DEGRADATION OF POLYANILINE FILMS

E. TOBOLKOVÁ^a , J. PROKEŠ^a , I. KŘIVKA^a , M. TRCHOVÁ^a , J. STEJSKAL^b

^aCharles University Prague, Faculty of Mathematics and Physics, Ke Karlovu 5, CZ-12116 Praha 2, Czech Republic

^bInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-162 06 Praha 6, Czech Republic

Ageing of polyaniline hydrochloride films [1] in relation to elevated temperature and defined air humidity was investigated. Samples were placed for 85 hours at 90°C in an atmosphere of constant relative humidity (RH) ranging from 30% to 90%. Time dependence of dc conductivity s (t) was measured in situ (FIG.1- s ₀ is the conductivity measured at 25°C and 50% RH). Initially, a simple decrease of s (t) represents a response to the temperature step. Subsequently, the shape of s (t) strongly depends on RH. It reaches a constant value for low RH, while for higher RH it is growing. The decay of s can be explained in terms of degradation of granular structure [2] while the mechanism of regeneration due to water molecules absorbed in the film remains under discussion. FTIR study of degraded films shows higher degree of deprotonation for films aged at atmosphere of higher RH.

FIG.1 Ageing of PANI hydrochloride films at 90°C for different humidity levels

[1] Stejskal J, Sapurina I, Prokeš J, Zemek J, Synth. Met. 105 (1999) 195.

[2] Wolter A, Rannou P, Travers J P, Giles B, Djurado D, Phys. Rev. B 58 (1998) 7637.

Acknowledgement. The research was supported by the Grant Agency of the Czech Republic (202/02/0698).

PC62

CHARGE TRANSPORT IN POLYANILINE DOPED WITH 3-NITRO-1,2,4-TRIAZOL-5-ONE

O. STARYKOV^a, J. PROKEŠ^a, I. KŘIVKA^a, J. STEJSKAL^b

^aCharles University Prague, Faculty of Mathematics and Physics, Department of Macromolecular Physics, Ke Karlovu 5, CZ-12116 Praha 2, Czech Republic

^bInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nam. 2, CZ-16206 Praha 6, Czech Republic

Polyaniline (PANI) base was protonated in aqueous solutions of an organic acid, 3-nitro-1,2,4-triazol-5-one (NTO) [1]. PANI-NTO represents a new type of material combining the properties of conducting polymer, PANI, and the features of an explosive, NTO [1]. Such materials could possibly be ignited by the Joule heat evolved by passing electric current. DC conductivity of PANI-NTO was measured in the temperature range 100 – 320 K; its temperature dependence seems to correspond to the theory of variable range hopping in three dimensions [2]. The narrow temperature range does not allow making a clear statement about the dimensionality of the charge transport in the studied polymer. The dielectric response of PANI-NTO was measured in the frequency range 20 Hz – 1 MHz and temperatures 100 – 320 K. The frequency dependence of AC conductivity also reflects the hopping nature of mobile charges. The activation energy of relaxation frequency is close to that of DC conductivity, showing that AC response originates from charge movement, not from the polarization of permanent dipoles. The activation energy for the samples with protonation degree above 0.085 remains constant with increasing dopant NTO concentration and DC conductivity. The value of this constant may correspond to the energy needed for the ionization of dopant counterion. The fit of electric relaxation function to the stretched exponential function gives the stretch parameter about 0.35, which shows that the distribution of relaxation times is wide and indicates the high inhomogeneity in the distribution of a dopant.

1. J.Stejskal, I.Sapurina, M.Trchová, J.Prokeš, Chem. Mater., in press.

2. N.F.Mott, E.A.Davis, Electron Processes in Non-Crystalline Materials, 2^nd ed., Clarendon Press, Oxford, 1979.

PC63

OPTICAL SPECTROSCOPY OF POLYSILYLENE FILMS

Y. V. DEMCHENKO^a, J. KLIMOVIČ^a, S. NEŠPŮREK^b

^a Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, CZ-18000 Praha 8, Czech Republic

^b Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-16206 Praha 6, Czech Republic

Optical spectra of polysilylenes have been ascribed to transitions between energy states of the "s -conjugated " system of electrons of the silicon main-chain atoms. If the side groups of the polymer contain a p -electron system, the energy states contain a contribution of a mixture of pi and sigma orbitals. A strong condition for an effective p -conjugation is the stiffness of the backbone of the molecule (or the chromophore). An array of singly bonded silicon chain atoms in polysilylenes is different. Its conformation can change easily due to the possibility of relatively free rotation around the chain single bonds. The extent of s -conjugation is thus a function of both the length and the conformation state of the oligomer or the polymer chain segments.

Harrah and Zeigler [1] observed changes in optical spectra on cooling polysilylene solution and explained them by temperature changes in the conformational preferences of the chains. They also observed a considerable red spectral shift in stress-oriented polysilylene samples.

Here we report the changes of both absorption and luminescence spectra of polysilylene films caused by the change of temperature in the region from the room temperature down to several tens K. In this temperature region, the polymers are deep in their glassy state and only weak conformation change can occur.

In the absorption measurements were detected the relative changes in the transmission of the samples caused by the changes in their temperature, the fluorescence measurements were taken in the time-resolved regime.

The observed temperature shift of the absorption maxima and their broadening seem to imply that temperature motion, at least at low temperatures, can make the conjugation more effective. The observed spectral changes of fluorescence on heating the samples from low temperature upwards suggest a positive role of the rise of temperature on the effectivity of excitation energy transfer in this region.

[1] L.A.Harrah and J.M.Zeigler, Macromolecules 1987, 20, 601-608

(Electronic Spectra of Polysilanes)

PC64

THE ROLE OF MULTIBLOCK POLYETHER MICELLES DURING COPPER BRIGHT ELECTRODEPOSITION

N. TABAKOVA^a, V. MIRCHEVA^b, J. STEJSKAL^c, I. POJARLIEFF^a

^aInstitute of Organic Chemistry, The Bulgarian Academy of Sciences, Acad. Bonchev Str., Block 9, BG-1113 Sofia, Bulgaria

^bInstitute of Engineering Chemistry, The Bulgarian Academy of Sciences, Acad. Bonchev Str., Block103-В, BG-1113 Sofia, Bulgaria

^cInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovskeho nam. 2, CZ-162 06 Praha 6, Czech Republic

During copper (Cu) electrodeposition in the absence of multiblock polyethers (MBPE) or at MBPE concentrations below critical micelle concentration (CMC) we have obtained non-bright coatings with enhanced roughness while, at MBPE concentrations above the CMC, the resulting coatings were bright with over 88% levelling. In aqueous solutions, MBPE are known to form micelles with a core of poly(propylene oxide) segments and a crown of poly(ethylene oxide) segments. In the presence of metal cations, the crown forms complexes therewith, and if organic compounds are present, they are included in the core. The latter leads to considerable increase in the size of the micelle. In the studied electrolyte, we have established that there were two types of micelles: micelles of only MBPE, which comprised the greater portion, and a smaller number of micelles of MBPE, which contain in their cores nitrogen and sulphur compounds, captured from the electrolyte. The crowns of both types of micelles form complexes with the Cu cations and are directed to the uneven cathode surface. The larger micelles, loaded with the nitrogen and sulphur containing organic compounds are predominantly chemisorbed on the convexities of the cathode and therefore they remain there after deionisation and block Cu deposition at those sites. Auger analysis in the presence of CMC of MBPE has confirmed the presence of nitrogen and sulfur only on convex sites. On the other hand, the smaller MBPE micelles are allocated to the concavities and after deionisation they re-enter the electrolyte, form Cu complexes again, and transfer Cu to the cathode surface. The process is continuously repeated, conferring the controlled nature of deionisation, which ultimately results in the deposition of highly levelled, mirror-bright copper coating with good physical and mechanical properties.

PC65

PROPERTIES OF PPy/POLYURETHANE BLENDS CAST FROM WATER-BORNE LATICES

J.NIZIOL^1,2, M.CHOUIKI², G.BOITEUX², J.ULANSKI³

¹ Faculty of Physics & Nuclear Techniques, University of Mining and Metallurgy, al. Mickiewicza 30, 30-059 Kraków, Poland

² Laboratoire des Materiaux Polymeres et Biomateriaux, UMR 5627 CNRS – Claude Bernard Lyon1 University, 43, Bd. du 11 Novembre 1918, 69622 Villeurbanne, France

³ Department of Molecular, Technical University of Lodz, ul.Zeromskiego 116, 90-924 Lodz, POLAND

For more than 20 last years intrinsically conducting polymers has been extensively studied. Despite a lot of effort done, none of common solvents was found to be able to dissolve any of polymers of this type. One of routes which enable processing of intrinsically conducting polymers is preparation of their latices.

In this paper some recent investigations of PU water-borne latex covered with PPy layer (core-shell type) and its composites with pure PU latex is presented. The diameter of core-shell latex particles was measured 75 nm on average and the core thickness of about 5 nm. By electronic microscopy it was found that the conducting phase doesn’t coalesce to form continuous interpenetrating network similar to those observed, for example, in composites containing doped polyaniline cast from m-cresol. The actual network resembled well organised ”grape-like” structures.

The percolation threshold of electrical conductivity was found at about 20% (regarding the volume of conducting core-shell). However if one remember that PPy makes only a quarter of core-shell latex, the PPy content at the percolation threshold is equal to about 5%. It was also found that mechanical properties of such composites were not severely altered comparing to the properties of the matrix.

Finally, the electrical conductivity was measured in function of temperature and an appropriate model of the conduction mechanisms in such materials was proposed.

PC66

PYRAZOLOQUINOLINES – ALTERNATIVE CHROMOPHORES FOR ORGANIC LED FABRICATION

J.NIZIOL^1,4, P.ARMATYS¹, A.DANEL², J.SANETRA³, E.GONDEK³, G.BOITEUX⁴

¹ Faculty of Physics & Nuclear Techniques, University of Mining and Metallurgy, al. Mickiewicza 30, 30-059 Kraków, Poland

² Departament of Chemistry, Hugon Kollataj Agricultural University, al. Mickiewicza 24/28, 30-059 Kraków, Poland

³ Institute of Physics, Cracow University of Technology, ul. Podchorążych 1, 30-84 Kraków, Poland

⁴ Laboratoire des Materiaux Polymeres et Biomateriaux, UMR 5627 CNRS – Claude Bernard Lyon1 University, 43, Bd. du 11 Novembre 1918, 69622 Villeurbanne, France

The application of organic materials in light-emitting diodes LED has been recently an object of both scientific and industrial interest. Potentially, it could be possible to fabricate a low-cost full-colour RGB device. Good emission in one of three necessary colours – the green is already available. However, despite efforts done by different groups and a significant number of papers published, the problem of obtaining ”good” emission in the red and in the blue is still open.

In this poster we would like to propose some new chromophores which could be used in this purpose. They all belong to pyrazoloquinoline (PAQ) family (fig.1). Their emission properties were tuned by side groups substitution. All of them were characterized by absorption and photoemission spectroscopy. According to the emission wavelength observed and calculated quantum efficiency in solution, some of them were used (in dispersion in PVK matrix) as the emissive layer in LEDs. These LED were fully studied by I(V), L(V), C(V) methods. The impact of different parameters like doping level by PAQ, thickness, ITO treatment etc. on features of the fabricated LEDs are disscussed.

fig.1 General scheme of pyrazoloquinoline

PC67

irreversible chemical transformation modes of polysilanes. An overwiev

J. PospÍŠIl, S. NeŠPŮREK

Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague, Czech Republic

Sigma-conjugation of the Si-Si backbone substituted by alkyls, aryls or their combination is a basic condition for appropriate electrical properties of polysilanes (PSi). Semiconductive ability of PSi is based on delocalization of the σ-conjugated electron system. Any irreversible chemical or phototriggered change affecting or even breaking σ-conjugation results in changes in photophysical properties of PSi. The complex mechanism of degradation modes affecting the Si-Si backbone and transformations on the silicon atom are not exactly understood. Potential transformations on hydrocarbon side groups are considered as less important than irreversible formation of reactive species on silicon atom arising after absorption of light in the range 254-400 nm and mainly σ-σ^* excitation.

PSi are rather sensitive to environmental attack of heat and phototriggered reactions with oxygen. Inherent or adventitious impurities arising from PSi synthesis or migrating from environment, including active species arising in contact polymers and catalyzing or initiating degradation by intermolecular effects have to be considered. Photosensitivity of PSi is affected by the structure of PSi (linear or branched backbone, inductive effects of side groups), phase (solid, solution) and exposure conditions (wavelength of the radiation, surrounding atmosphere). Chain scission appears to be the principal process in PSi containing exclusively alkyl substituents. Substitution by an aryl enhances photostability against chain scission, in the solid state in particular. Photocrosslinking is preferred as a transformation mode. An overview is given on potential irreversible processes involving formation of terminal and in-chain silyl radicals by phototriggered homolysis, secondary processes including selfreractions of silyls (recombination, branching, crosslinking, disproportionation, cyclisation), and intermolecular reactions with reactive species such as oxygen, unsaturation or oxygenated structures in contact polymers. Processes accounting in formation of carbon-centered radicals on alkyl substituents are considered as a minority process resulting in C-C crosslinks or oxygenated structures.

Acknowledgement. Financial support by grant A1050901of Grant Agency of the Academy of Sciences of the Czech Republic and technical cooperation of Ms D. Dundrová are gratefully appreciated.

PC68

the influence of morphological and conformational changes on the molecular mobility of pEn

N. Zouzou^a, D. Colombini^b, J. J. Martinez-Vega^a

^a Laboratoire de Génie Electrique de Toulouse (UMR-CNRS 5003), Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, FRANCE.

^b Department of Polymer Science & Engineering, Center for Chemistry and Chemical Engineering, LUND University, Box 124, 22100 Lund, SWEDEN.

zouzou.nori@lget.ups-tlse.fr

ABSTRACT: Both dynamic electrical and dynamic mechanical analyses, DEA and DMA, were successfully combined to explore the relaxational process in amorphous and semi crystalline poly(ethylene 2,6 naphthalene dicarboxylate) (PEN) samples which are increasingly replacing some common dielectrics (polypropylene, poly ethylene terephthalate,…) in several electrical applications.

Several morphologies of the material were obtained using an isothermal crystallization from an amorphous glassy state. The differential scanning calorimetry (DSC) measurements were carried out to study the characteristic temperatures of the material and to calculate the crystallinity rates (c %). A sigmoïdal evolution of c , representative of the nucleation/growth processes of the crystalline entities, is evidenced. Conformational changes of polymer chains, due to the return to ambient temperature of the samples, have been analyzed by FT-IR spectroscopy. During the isothermal crystallization, the conformational transition from gauche to trans conformation takes place while crystallinity increases.

The electrical and mechanical responses of the samples confirm the existence of two secondary relaxations b and b *, the main relaxation a and the r -process. The molecular assignments of b , b * and a relaxations are mentioned.

The DMA results clearly identified the above-T_g loss factor peak, r , as a probe of the cold crystallization occurring in amorphous samples and samples with low crystallinity. It was shown that the r -peak disappeared with the disappearance of the DSC cold crystallization peak and the appearance of a pre-melting peak.

Using the DEA response, a model of r -peak variation is proposed. The proportionality of the loss factor peak amplitude with the inverse of frequency indicates a non-thermal activation process which exhibits electric charge mobility, and could be considered as an anti-primary relaxation.

Combining the DMA and DEA investigations showed that the r process is governed by both electrical and non-electrical aspects. The ambiguity related to this relaxation in the literature could find its source in such a bimodal origin.

PC69

influence of morphology AND MEASURMENT METHODOLOGY on electrical Conductivity in PEN.

J.F. CHAVEZ, J.J. MARTINEZ-VEGA, N. ZOUZOU, J. GUASTAVINO

Laboratoire de Génie Electrique de Toulouse (UMR-CNRS 5003)

Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, FRANCE.

fchavez@lget.ups-tlse.fr

The polymers find an important field of application in the electrical industry because of their utilization in electrical systems as insulators as dielectrics. The challenge over the last several years had been to make electrical compounds smaller in size. In that way the material’s morphology is of strategic importance in the performance of new components in relation with the geometry asked for in our days. Therefore, it is important to know the influence of different types of stress on the electrical properties of the materials.

In this perspective, we have studied the influence of the crystallinity rate over electrical conduction characteristics of the PEN (Polyethylene-2,6-Naphthalene Dicarboxylate) which is increasingly replacing some dielectrics (polypropylene and polyethylene terephthalate) in certain electrical applications.

Starting from an amorphous morphology of PEN, samples with several crystallinity rates were obtained and analyzed using Differential Scanning Calorimetry (DSC) in order to identify their thermal characteristics.

Moreover, measurements of charging and discharge currents were carried out on PEN samples to characterize their electrical properties. The steady state current observed after 120minutes, in response to the electric field, shows an increase of the insulator resistivity with the crystallinity rate. The increase in the crystallinity rate favors the diminution of the free volume, so the movement of charges is restricted especially by the species with important sizes.

During conduction experiments the need for a new methodology of obtaining I(V) curves seems to be appropriate in several ways. It was demonstrated that at low fields, 30mn of polarization was more than enough to allow an important decay of orientation dipolar current. The total time for polarization and depolarization is indisputably optimized. On the other hand, at high fields, a short duration (some minutes) under electric field is quite sufficient to attain the steady state, which minimizes material’s evolution.

Theses results suggest a new measurement methodology of electrical field applications based at the field level and on the slope of I(V) curves.

PC70

TRAPPING SITES IN LADDER-TYPE POLY(p-PHENYLENE)

E. DOBRUCHOWSKA^a, I. GLOWACKI^a, B. LUSZCZYNSKA^a, J. ULANSKI^a

D. NEHER^b, U. SCHERF^c

^a Department of Molecular Physics, Technical University of Lodz,

Zeromskiego Str. 116, 90-924 Lodz, Poland

^b University of Potsdam, Institute of Physics,

Am Neuen Palais 10, D-14469 Potsdam, Germany

^c University of Postdam, Institute of Chemical Physics and Theoretical Physics

Karl-Libknecht Str. 24-25, D-14476 Golm, Germany

Ladder-type poly(para-phenylene)s (LPPPs) are, among conjugated polymers, particularly promising materials as components for opto-electrical devices due to their planar topology, corresponding to two-dimensional-like conjugation, which is favourable for charge carriers transport [1].

Trapping of charge carriers influences both photoconductivity and electroluminescence phenomena. One of the most adequate methods of investigation of charge carriers trapping, detrapping and radiative recombination processes in polymers is thermoluminescence (TL) [2].

In this work we present TL investigations for LPPP neat and doped with triphenylamine derivative (TPTA). The TL measurements were carried out for polymer films in the temperature range 15-325 K. The TL spectrum for neat LPPP shows one relatively narrow maximum at 50 K with small high-temperature shoulder at about 100 K. Introduction of TPTA causes a shift of the TL maximum towards higher temperatures. This indicates an increase of population of deeper traps. In order to determine the activation energies of detrapping processes the partial heating experiments were carried out for the investigated systems. The mechanism of radiative recombination giving rise to the observed TL maximum is discussed on a basis of spectral analyses of thermoluminescence. The results indicate that the recombination processes occur from triplet states.

[1] J. Pan, U. Scherf, A. Schreiber, R. Bilke, D. Haarer, Synth. Met. 115, 79 (2000).

[2] I. Glowacki, J. Ulanski, B. Kozankiewicz, in:J. C. Fothergill and L. A. Dissado (Eds.), ”Space Charge in Solid Dielectrics”, 1998, pp. 251.

This work was partially supported by KBN, project No 3 T09A 079 19.

PC71

INFLUENCE OF CHARGE CARRIER RECOMBINATION ON THE PHOTO-INDUCED DISCHARGE

J. JUNG, I. GLOWACKI, J. ULANSKI

Department of Molecular Physics, Technical University of Lodz,

Zeromskiego Str. 116, 90-924 Lodz, Poland

The recombination processes influence significantly both photogeneration and transport of charge carriers, therefore it is a crucial phenomenon for the photoconductivity performance, especially in disordered materials like polymers.

Photo-induced discharge technique is widely used for investigations of photoconductive materials. A decay rate of the surface potential upon illumination depends on the quantum yield of photogeneration but it can be also dependent on the recombination - both phenomena occur in the same time scale. We propose model describing the influence of the recombination on the decay rate of surface potential. This model is applied to analyse the results obtained for series of N-carbazolyl substituted polysilanes and poly(N-vinylcarbazole) doped with low molecular weight acceptor, 2,4,7-trinitrofluorenone.

Analysis of the electric field dependence of the recombination cross-section determined from photo-discharge has indicated, that recombination has only negligible influence on the effective photogeneration in polysilanes with low density of the N-carbazolyl groups. However, with increasing degree of the substitution, strong influence of recombination of charge carriers on photo-discharge is observed.

PC72

INFLUENCE OF SUBSTITUTION WITH N-CARBAZOLYL GROUPS ON CHARGE CARRIER TRAPPING AND RECOMBINATION IN POLYSILANES

I. GLOWACKI, E. DOBRUCHOWSKA, B. LUSZCZYNSKA, J. ULANSKI

Department of Molecular Physics, Technical University of Lodz,

Zeromskiego Str. 116, 90-924 Lodz, Poland

Silicon backbone linear oligomers and polymers show interesting photophysical properties associated with s conjugation along the Si chain.

We present absorption, photoluminescence (PL) and thermoluminescence (TL) investigations for series of N-carbazolyl substituted silane homo- and copolymers. Polysilanes exhibit intensive near-UV absorption and strong PL. It was found that the optical absorption bands of the carbazolyl side groups superimpose on those of the Si backbones in the ultraviolet spectrum region. This feature reduces Si-Si bonds photodegradability during UV irradiation.

In the photoluminescence spectra a red-shift of PL bands was observed when the density of the N-carbazolyl groups was increasing. Similar results were obtained by S. Mimura et al. [1]. The TL spectra obtained in a broad temperature range (15 – 325 K) show that the N-carbazolyl side groups act as trapping sites in polysilanes [2]. Spectral analysis of the light emitted during the TL experiments indicates that monomeric mechanism of luminescence operates at low temperatures while excimeric mechanism dominates at higher temperatures. For higher substitution with the N-carbazolyl side groups both the shape and the spectral characteristics of the TL spectra become similar to those for poly(N-vinylcarbazole).

[1] S. Mimura, H. Naito, T. Dohmaru, Y. Kanemitsu, M. Aramata, Appl. Phys.Lett. 77 (2000) 2198 - 2200.

[2] I. Glowacki, E. Dobruchowska, J. Ulanski, Synth. Met. 109 (2000) 139 - 142.

PC73

New application of UV stabilizer of polymers:
5-CHLORO-2-(2-hydroxy-5-methylphenyl)benzotriazole

Aleksandra Lewanowicz

Institute of Physical and Theoretical Chemistry, Politechnika Wrocławska, Wybrzeże Stanisława Wyspiańskiego 27, PL 50-370 Wrocław, Poland

Characteristic feature of o-hydroxyphenylbenzotriazoles is rapid radiationless deactivation after UV excitation of the first excited singlet state. As the enol-keto photo-transformation operates, electronic energy is readily converted into heat [1]. That spectral behavior is a crucial point for their industrial application [1, 2]. Energetic as well as kinetic properties are known because of the intensive study since in the past [1, 2]. However, experimental investigations were focused on molecular properties of this class of compound.

In this work, we present results of optical study of 5-chloro substituted 2-(2’-hydroxy-5’-methylphenyl)-benzo-triazole (see figure on the left). Good quality single crystal was UV excited at room temperature [3]. Highly Stokes-shifted luminescence peaked at 16000 cm^–1 was observed.

Using microscopic detection method of this red luminescence of the keto- form in crystals, a new effect was observed: guiding and amplification of spontaneously emitted light. However, maximum of the transferred light inside micrometer size crystal was slightly high-energy shifted in relation to the red emission [3]. This effect we call TINSEL: Transfer In Needle of Spontaneously Emitted Luminescence. TINSEL gives a new possibility of application of 2-(2’-hydroxy-5’-methylphenyl)-5-chlorobenzotriazole as wave guiding organic material.

1. H. J. Heller and H. R. Blattman, Pure Appl. Chem., 30(1972)145; A. Gupta, G. W. Scott, D. Kliger and O. Vogl in: Polymers in Solar Eenergy Utilization, D. J. Williams and R. D. Deanin (Eds) ACS Symposium Series 220, American Chemical Society 1983, ch. 19; H. E. A. Kramer in: Photochromism. Molecules and Systems, H. Durr and H. Bonas-Laurent (Eds), Elsevier, Amsterdam 1990, pp. 654-681 (and references therein); N. A. Evans, J. Rosevear, P. J. Waters and J. Wilshire, Polym. Degrad. Stab., 14(1986)263; S. W. Bigger, K. P. Ghiggino, I. H. Leaver, A. D. Scully, J. Photochem. Photobiol. 40(1987)391.
2. H. Shizuka, K. Matsui, Y. Hirata, I. Tanaka, J. Phys. Chem., 80(1976)2070, A. L. Huston, G. W. Scott and A. Gupta, J. Chem. Phys., 76(1982)4978; M. Wiechmanm, H. Port, F. Laermer, W. Frey and T. Elsaesser, Chem. Phys. Lett., 165(1990)28.
3. A. Lewanowicz and F. Baert, Acat Cryst. C50(1994)801.
4. A. Lewanowicz, SPIE, 4413(2001), 404

PC74

ORIGIN OF THE BAND BENDING IN COPPER-PHTHALOCYANINE THIN FILMS

H. YAMANE^a, S. KERA^a, S. TANAKA^a, H. HONDA^a, T. NAKAMURA^a, H. SETOYAMA^a, K.K. OKUDAIRA^b, N. UENO^a

^aGraduate School of Science and Technology, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

^bInstitute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, Japan

e-mail: yaman.16@xtal.tf.chiba-u.ac.jp

High-resolution UPS were measured for copper-phthalocyanine (CuPc) thin films prepared on graphite (HOPG) substrate as a function of the film thickness. Figure 1 (a) shows the high-resolution UPS in the highest occupied molecular orbital (HOMO) region for CuPc/HOPG as a function of the film thickness. The continuous binding energy (E_B) shift of HOMO with the film thickness is clearly seen. From outermost-surface spectroscopy using metastable atoms, on the other hand, it was found that CuPc molecules orient flat on the HOPG surface for the monolayer and gradually tilt with increasing the film thickness. It is considered that the observed E_B shift in UPS originates from the difference of the polarization energy of the molecule due to the continuous change of the molecular orientation. Furtheremore, we observed the separated HOMO peaks (A and A’) by annealing 400Å-thick-CuPc at 230 °C for 6 hours. The E_B positions of peak A and A’ agree well to the E_B positions of the flat and tilted CuPc, respectively. This originates from the domain separation of the flat and tilted CuPc by the annealing [see Fig. 1(b)]. These results suggest that the continuous change of the molecular orientation can be an important origin of the band bending as illustrated in Fig. 1(c).

PC75

PHASE TRANSITIONS IN POLY(HEPTANE-1,7-DIYL BIPHENYL-4,4´-DICARBOXYLATE) - SAXS, WAXS AND DSC STUDY

M. KRASTEVA^a, G. TODOROVA^a, E. PÉREZ^b, M. MARUGÁN^b

^aSofia University, Faculty of Physics, Department of General Physics, James Bourchier 5 Blvd., 1126 Sofia, Bulgaria

^b Instituto de Ciencia y Tecnología de Polímeros, Juan de la Cierva 3, 28006 Madrid, Spain

The main-chain thermotropic liquid-crystalline poly(hepthamethylene b,b'-bibenzoate) was investigated by means of Small-Angle X-ray Scattering (SAXS), Wide-Angle X-ray Scattering (WAXS), and Differential Scanning Calorimerty (DSC). Nonisothermal crystallisation method, with different rates of cooling and heating, was applied.

On cooling, two phase transitions are observed, whereas on heating only transition is seen on the DSC runs. Starting from cooling of the sample, the transitions were recognized as I-Sm (isotropic melt- smectic) and Sm-Cr (Sm-3D crystalline structure transitions, and on heating only transition is attributed to Cr-I transition[1].

On cooling, at high temperatures, only amorphous halo is presented in WAXS region. With cooling down the system, in SAXS region, a single peak appears with d-spacing of about 1.74 nm, d_s. This peak is connected with a smectic type structural formation. At the same tempratures, there is no change on WAXS curve. In low temperature region SAXS peak still exists, but its value decreases up to about 1.68 nm. In WAXS patterns, six crystalline peaks are clearly seen.

On heating in WAXS all six peaks are presented up to the isotropisation temperature. In SAXS area the single peak d-spacing gradually increases.

Temperature dependencies of d-spacings of all crystalline peaks and d_s were derived. Degree of crystallinity was established, based on the integrated intensities of the crystalline peaks and amorphous halo, depending on the temperature.

1.Pérez E, Pereña J, Benavente R, Bello A Handbook of Engineering Polymeric Materials; New York-Basel-Hong Kong, (1997), 383-397

PC76

PHOTOCHROMIC AZOBENZENE-CONTAINING CROWN ETHERS - EXPERIMENT AND QUANTUM-CHEMICAL CALCULATIONS

K. JANUS, A. OLSZOWSKI, J. LIPIŃSKI AND J. SWORAKOWSKI

Institute of Physical and Theoretical Chemistry, Wrocław University of Technology, Wyb. Wyspiańskiego 27, 50-370 Wrocław, Poland

Janus@kchf.ch.pwr.wroc.pl

Photochromic azobenzene derivatives are among the most promising molecules for optical information processing and storage. The derivatives with the azobenzene moiety incorporated in crown ethers (Fig. 1) have been investigated in this laboratory because of their shapes expected to allow for the kinetics of the photochromic reaction be almost independent of the environment (e.g. in polymer matrices or liquid solutions).

The mechanism and kinetics of the reversible trans-cis photoisomerisation obtained from measurements of the temporal evolution of UV-VIS absorption spectra was presented in our previous papers [1-3]. This contribution will focus on the comparison of UV-VIS absorption spectra of the molecules under study with results of quantum-chemical calculations.

1. K. Janus, J. Sworakowski, A. Olszowski, A. Lewanowicz, J. Lipiński, E. Lubicz and J.F. Biernat, Adv. Mat. Opt. Electron., 1999, 9, 181.

2. K. Janus, K. Matczyszyn, J. Sworakowski, J.F. Biernat and Z. Galewski, Mol. Cryst. Liq. Cryst., 2001, 361, 143.

3. K. Janus, J. Sworakowski and E. Luboch, Chem. Phys., to be published (2002).

PC77

POLYDIACETYLENE NANOWIRES IN ULTRA-THIN FILMS

M. ALLOISIO, D. CAVALLO, C. DELL' ERBA, C. CUNIBERTI, G. DELLEPIANE

INFM, INSTM, Dipartimento di Chimica e Chimica Industriale, Università di Genova - Via Dodecaneso, 31 - I-16146 Genova, Italy

Here we report on the organization in ultra-thin films prepared from polydiacetylenes (PDAs) with cylindrical molecular shapes. PDAs are themselves one-dimensional semiconducting polymers that exhibit very interesting electronic and optical properties. These properties, related to the conjugated polymer backbone made of alternating double and triple bonds, can be modulated by the appropriate choice of the chemical nature of the double bond substituents. One of the most interesting member of this class of conjugated polymers is polyDCHD, in which the side groups are given by photoconductive carbazolyl rings. We have recently prepared novel PDAs from diacetylenes homologous to DCHD carrying long alkyl or acyl substituents at the 3,6 positions of the carbazolyl groups.

Powder X-rays diffraction studies have shown that both classes of polydiacetylenes exhibit hexagonal columnar (Col_ho or Col_hd) architectures. The columns, that represent the conjugated skeleton with the carbazolyl rings, are formed by disk-like units at the distance of 0.47 nm. In the Col_ho structure the repeating units are superimposed in an ordered way, while in the Col_hd structure no strict correlation among adj acent units is present. The diameter of the columns is 3 .4 nm. The intercolumnar distance is related to the length of the alkylic or acylic groups and falls in the range 3.2÷3.9 nm.

Spectroscopic and molecular properties have been determined on the polymers in solution.

Ultra-thin polymeric films have been prepared on different substrates by spincoating of polymers or monomers solutions. The films organization has been studied by SEM and X-rays diffraction. Linear and nonlinear optical properties have been determined on these films.

PC78

MONO- AND DIALKYL-SUBSTITUTED (PYRROL-2-YL)FLUORENE – NEW SENSORIC MATERIALS

A. CHYLA⁺ AND J. SOŁODUCHO^#, D. J. WALTON^$, A. MIROŃCZYK^*

⁺Institute of Physical and Theoretical Chemistry, Wrocław University of Technology, Wroclaw, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland

^#Institute of Organic Chemistry, Biochemistry and Biotechnology, Wrocław University of Technology, Wroclaw, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland

^$Coventry University, NES, Priory Street, Coventry, CV1 5FB, UK

^*University of Zielona Gora, Institute of Biotechnology and Environmental Protection, ul. Monte Caasino 21b, 65-561 Zielona Gora, Poland

For more than twenty years now polypyrrole and its derivatives have been widely investigated because of their easy electrosynthesis, excelent stability and very high and controlable electrical conductivity in oxidized state [1]. They may find an application in energy storage, solar energy conversion, electrochromic displays or optoelectronic devices. There is also no doubt about numerous applications that are, or may in the nearest future be addressed by gas and/or chemical sensors detecting the presence and concentration of chemical species. The great hopes and expectations are associated with conducting polymer sensors. Recently we have reported about a unique synthesis of 1,4-bis(pyrrol-2-yl) arylenes that opens up a numerous opportunities for the synthesis of derivatized, potentially soluble and processable pyrrole containing conducting polymers [2].

An investigations of the electrical conductivity of Langmuir-Blodgett (LB) films consisting one or several monolayers of 9- and 9,9 dihexadecyl pyrrole(-2-yl) fluorene, a precursor of the new conducting polymer, exposed to different concentrations of nitrogen dioxide and ammonia were carried out. The films were deposited onto a set of eight interdigital, burried Au electrodes (200 m m. wide and spaced) photo-lithographically fixed on SiO₂ coated silicon substrates. Electrical properties of gold contacts to these LB films were evaluated by current-voltage characteristics, which are linear over the whole measuring range. Very short response times, good reproducibility and fair sensitivity at room temperatures make these materials a very promissing candidates for neuron network sensing elements.

1. D. J. Walton, C. E. Hall, A. Chyla, “Functional dopants in conducting polymers”, Synth. Metals, 45 (1991) 363-371.

2. J. Sołoducho, S. Roszak, A. Chyla, K. Tajchert, “Synthetic routes to bis(pyrroyl)arylenes. Experimental and molecular modelling studies”, New. J. Chem., 25 (2001) 1175-1181.

PC79

ORGANIC ELECTROLUMINESCENT DEVICES CONTAINING PHOSPHORESCENT MOLECULES IN MOLECULARLY-DOPED HOLE-TRANSPORTING LAYER

W. STAMPOR^a, J. MĘŻYK^a, J. KALINOWSKI^a, M. COCCHI^b, D. VIRGILI^b,

V. FATTORI^b, P. DI MARCO^b

^aDepartment of Molecular Physics, Technical University of Gdańsk, ul. G. Narutowicza 11/12, 80-952 Gdańsk, Poland

^bInstitute of Photochemistry and High Energy Radiation (FRAE), C.N.R., via P. Gobetti 101, 40129 Bologna, Italy

Phosphor-containing organic light-emitting diodes (LEDs) are of interest because of their high quantum efficiency as compared with purely fluorescent LEDs. We demonstrate a high efficiency simple electrophosphorescent devices comprised of 4,4’,4’’-tris(3-methylphenyl-phenylamino) triphenylamine (m-MTDATA) dispersed in a polycarbonate (PC) matrix as a hole-transporting layer (HTL), and 2-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as an electron-transporting layer (ETL). The HTL doped with the metallorganic phosphor, fac- tris(2-phenylpyridine) iridium [Ir(ppy)₃] and/or 5,6,11,12-tetraphenylnaphthacene (rubrene º Rb) fluorescent dye is shown to act as the emitter. The devices exhibit external quantum efficiencies (QE) between 0.1% ph/carrier up to over 10% ph/carrier dependent on the content of the emitter and the device driving current. The emission spectrum of all devices is characteristic of the dopants either the phosphorescence of [Ir(ppy)₃] or fluorescence of Rb when doped separately, and their combination if both dispersed in the HTL. Since the photoluminescence (PL) and electroluminescence (EL) spectra of dopant - free bilayer (m-MTDATA:PC) /PBD system is due solely to the exciplexes formed between electron donor (m-MTDATA) and electron acceptor (PBD) compounds, an efficient exciplex ® dopant molecule energy transfer is assumed to occur within doped emitters. Whereas the PL and EL spectra of the [Ir(ppy)₃]-doped only emitters perfectly coincide, they differ significantly when both [Ir(ppy)₃] and Rb are present in the emitter. These differences are explained by an additional formation mechanism of the excited states, occurring in the EL process. This is due to the direct electron-hole recombination on Rb molecules. The presence of both phosphorescent and fluorescent dopant in the emitter shifts the maximum QE towards large current densities. We discuss briefly various electronic processes underlying the current-dependent QE.

PC80

THE PERCULARITIES OF ELECTRICAL PROPERTIES OF POLYPROPYLENE - SHUNGITE COMPOSITES

TIMOFEEVA V.A., KEDRINA N.F., SOLOVIEVA A.B., TCHMUTIN I.A.*, RYVKINA N.G.*

Institute of chemical physics RAS, 119991, Kosygina ul.,4, Moscow, Russia

e-mail: anna@chph.ras.ru

* Institute of Radioengineering & Electronics RAS, 141190, Fryazino, Moscow Region,

1 Vvedenskii sq., Russia

The mechanical and electrical properties of composites containing polypropylene (PP), shungite filler (SF) and rubber powder (RP) was studied. Shungite with 98 wt.% carbon content was used. Average particle size of rubber powder was <200m m. SF was produced by powdering of Karelian shungite rocks, the particle size of shungite powder was 2-8 m m.

Earlier conducting composities of PP and shungite filler of two types - with carbon content 98% and 30% were obtained. It is possible to vary conductivity of compositions over a wide range and to obtain both the conducting materials with conductivity on a direct current s _dc = 2*10^-5 (Ohm/cm )^-1, and materials possessing antistatic properties, using SF. Thus the percolation threshold for SF (without dependence from carbon content) is ~ 30 wt.%. The analysis of mechanical characteristics has shown that the introduction SF in a polymeric matrix increases composite rigidity, but is accompanied by a falling of plastic properties.

In this work dc-conductivity (s _dc), temperature (Т) dependence of conductivity and coefficient of anisotropy of conductivity К=s _{dc½ ½} /s _dc^ for composites PP + RP + SF (content of a rubber powder - 20 wt%) and PP + SF, was measured depending on a shungite content. The introduction of a rubber powder has increased of composites conductivity on magnitude from one up to five orders, and s _dc has increased monotonically with concentration of РК. The examination of dependences of conductivity from SF concentration has shown, that the increasing of conductivity is due to reduction of a percolation threshold. So, the change of RP concentration from 0 up to 20 % reduced of a percolation threshold from 30 up to 26 %. This effect is caused by increase of SF real concentration in PP at presence in composite of RP nonconducting particles. Also the introduction RP changed of temperature dependence of conductivity at concentrations SF near a percolation threshold. In the investigated region of fillers concentrations s (Т) depends on a thermal expansion coefficient of a matrix, the magnitude which one varies at variation of concentration of a rubber powder.

The investigation of anisotropy of conductivity has shown, that for three-component systems К depends from thickness of a sample. So, К is > 1 for such samples, thickness of which is greater than particle size of rubber powder by an order and more. If this requirement is not fulfilled, К is ~ 10^-3 - 10^-5.

PC81

EFFECT OF ADSORBED CHLORODIFLUOROMETHANE ON THE DENSITY-OF-STATES IN METAL-FREE PHTHALOCYANINE

I. ZHIVKOV^{a, b}, G. DANEV^a, S. NEŠPŮREK^b, J. SWORAKOWSKI^c

^aCentral Laboratory of Photoprocesses, Bulgarian Academy of Sciences,

7.  
8. Bonchev Str., 109, 1113 Sofia, Bulgaria

^bInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, CZ-162 06 Prague 6, Czech Republic

^c3Institute of Physical and Theoretical Chemistry, Technical University of Wroclaw, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland

The influence of adsorbed chlorodifluoromethane (CHClF₂) on the density-of-states (DOS) function h(E) in metal-free phthalocyanine (H₂Pc) thin films was investigated by thermomodulated space-charge-limited-current (TM-SCLC) spectroscopy [1,2]. The method allows to directly determine the h(E) function from an SCL current-voltage characteristic and the dependence of the activation energy of the current on the applied voltage, without any preliminary assumption concerning the shape of the DOS function.

Four well-defined local levels were detected within the energy range 0.5 - 0.3 eV in thin films of H₂Pc, accompanied by onset of a manifold of shallower states [3]. The exposure of the film to CHClF₂ mixed with N₂ led to the a slight decrease in the trap concentration (ca. 30 % for the CHClF₂ concentration 470 ppm). The other important effects were: a shift of the DOS spectrum to higher energies and broadening of peaks in the spectrum of localized states with increasing CHClF₂ concentration. Thus, for the distributed trap 0.26 eV deep, which is mainly of structural origin, the shift of energy from 0.26 eV (peak position) to 0.35 eV and the change in the half-width from 0.02 eV to 0.06 eV were observed at a CHClF₂ concentration of 350 ppm. The broadening effect is assumed to originate from the electron-dipole interactions [4] between H₂Pc and CHClF₂ molecules.

The work was supported by the Bulgarian Ministry of Education and Science (grant H 806), the Grant Agency of the Academy of Sciences of the Czech Republic (grant A1050901) and the Technical University of Wroclaw.

[1] S. Nešpůrek, J. Sworakowski, J. Appl. Phys. 51, 2098 (1980).

[2] F. Schauer, R. Novotný, S. Nešpůrek, J. Appl. Phys. 81, 1244 (1977).

[3] I. Zhivkov, S. Nešpůrek, J. Sworakowski, Acta Phys. Pol. 100, 215 (2001).

[4] H. Valerián, E. Brynda, S. Nešpůrek, W. Schnabel, J. Appl. Phys. 78, 6071 (1995).

PC82

NEW COPOLYMERS OF POLY(MALEIC ANHYDRIDE-co-STYRENE) WITH 1,3,4-OXADIAZOLE FOR ELECTROLUMINESCENT DEVICES

G. ALDEA^a, D. VÝPRACHTICKÝ^b, V. CIMROVÁ^b

^a "Petru Poni" Institute of Macromolecular Chemistry Iasi, Romanian Academy, Aleea Grigore Ghica Voda 41A, 6600 Iasi, Romania

(aldeagro@netscape.net)

^b Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, 162 06 Prague 6, Czech Republic Republic (vyprach@imc.cas.cz, cimrova@imc.cas.cz)

New functionalized copolymers of poly(maleic anhydride-co-styrene) containing 1,3,4-oxadiazole units as pendant groups were synthesized and characterized (Scheme I). An attachment possibility of the 2-(4-aminophenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole and 1-aminohexane by the amide bond was tested also with other aromatic amines ( 4-aminoazobenzene, 4-nitroaniline).

Scheme I

Copolymers with various content (x) of oxadiazole units were obtained and characterized their properties. UV/VIS, photoluminescence and transport properties of thin layer were studied. Synthesized materials will be used for the preparation of organic light-emitting devices (LEDs).

This research was supported by the Academy of Sciences of the Czech Republic

(project number AVOZ 4050913).

PC83

CHARGE CARRIER TRANSPORT AT LOW ELECTRIC FIELD IN p -CONJUGATED POLYMERS

G.JUŠKA^a, K.GENEVIČIUS^a, K.ARLAUSKAS ^a, R.ÖSTERBACKA^b, H.STUBB^b

^a Department of Solid State Electronics, Vilnius University, Saulėtekio 9, LT-2040 Vilnius, Lithuania gytis.juska@ff.vu.lt

^b Åbo Academy University, Department of Physics, Porthansgatan 3, FIN-20500

Turku, Finland rosterba@abo.fi

We will prove the reason of, by TOF measured, drift mobility decrease when electric field increases in low electric field region in organic polymers. The reason of this drift mobility decrease is caused by sufficient equilibrium charge carrier density, which induces the electric field redistribution during the time shorter than charge carrier drift through the interelectrode distance time. Experimentally this will be demonstrated in series of p -conjugated polymers (RR PHT, RR POM, PAM, PPV). These experimental TOF results will be compared with CELIV (charge carrier extraction by linearly increasing voltage) results (Fig.1). CELIV method allows measure the concentration and mobility of equilibrium charge carriers also in high bulk conductivity materials where TOF measurement results are erroneous.

Fig.1. Hole mobility measurement results

PC84

SPONTANEOUS ELECTRON LOCALISATION IN 2D LATTICES

L. BRIZHIK^a, A. EREMKO^a, B. PIETTE^b, W. ZAK.RZEWSKI^b

^aBogolyubov Institute for Theoretical Physics , Ukrainian National Academy of Sciences, Metrologichna Str., 14-b, 03150 Kyiv, Ukraine

^bDepartment of Mathematical Sciences, Durham University, Durham DH 1 3 LE, UK

The self trapped (spontaneously localised) electron states in a discrete anisotropic two-dimensional (2D) electron-phonon lattice are investigated numerically and analytically. It is shown that in the adiabatic approximation spontaneously localised electron states are formed when the parameters of the system take values in some finite intervals. Such electron states possess soliton-like features and are stable under the interactions with weak perturbations and collisions with boundaries at not too large values of their velocity. The continuum limit of the corresponding discrete equations is shown to lead to a two-dimensional modified nonlinear Schroedinger equation (2D MNLSE), which has an extra term when compared with the conventional 2D NLSE. This extra term comes from the lattice discretness and is shown to be essential to prevent the soliton from collapsing which takes place in the 2D NLSE. This is achieved in the isotropic lattices when the nonlinearity parameter, g, which is determined by the electron-phonon coupling, takes values within some finite interval g_c,1<g<g_c,2. It is shown, within the variational scheme, that the energy minimum is attained for the delocalised states provided g<g_c,1=5.85, and for the strongly localised states (essentially on one lattice site) provided g > g_c,2 8. The radius of the electron localisation, as a function of electron-phonon coupling constant, is evaluated and compared with the values obtained in numerical calculations of the initial system of discrete equations.

It is shown also that when the initial function is slightly different from the stationary state, its width oscillates around the value, that corresponds to the width of the stationary state. The stationary width of the solution and the frequency of it oscillations depend on the value of electron-phonon coupling. This dependence is given by the following expressions:

, w = 0.65 (g-g_c,1)^3/2

Some preliminary results on moving solitons in 2D lattices are also presented.

PC85

NANOSTRUCTURAL EFFECTS IN PLASMATICALLY PREPARED POLYSILYLENES

F. SchaueR, I. Kuřitka, n. dokoupil, p. horváth

Faculty of Chemistry, Brno University of Technology, Purkynova 118, Brno,CZ-612 00, Czech Republic

The photoluminescence of the plasma prepared polysilylanes from corresponding monomers, exemplified by poly[(methyl)phenylsilylane], is examined. For the preparation two quantitatively different plasmas were used: radiofrequency discharge (13,5MHz) and microwave discharge (2,45 GHz) in the regime of electron cyclotron resonance. We concentrated on the conditions where the 1D features of the polymers were preserved. Results for both optimised groups of materials exhibit similar results: the excitonic absorption band with maximum at 320- 360 nm, depending on the conditions of preparation. We explain the observed phenomena by the occurrence of the nano-sized 1D Si polymers embedded in 3D covalently bonded Si network.

PC86

EFFECT OF AGGREGATE FORMATION ON ELECTRONIC PROCESSES
IN SOLUBLE OLIGO(DIPHENYLVINYLENE)S

J. PFLEGER^a, M. PAVLÍK^a, J. VOHLÍDAL^b

^aInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06 Praha 6, Czech Republic

^bDept. of Physical and Macromolecular Chemistry, Laboratory of Specialty Polymers, Charles University, Albertov 2030, 128 40 Prague 2, Czech Republic

The substitution of -conjugated chains by planar sidegroups may leed to the aggregate formation that usually decreases the electroluminesce efficiency and shifts the emission towards longer wavelength. We focused on the photoelectrical and photoluminescent properties of three types of soluble and chemically stable oligo(diphenylvinylene)s differing in the main-chain end-groups:
(i) diphenylmethylenediyl (PDA), (ii) phenylcarbonyl (PDAC), and (iii) fluorene-9,9-diyl (PDAF).

The end groups were found to affect the excitation energy relaxation of oligomer molecules significantly. The PDA oligomer shows strong photoluminescence in the blue spectral region. In the PDAC oligomers the fluorescence quenching was observed; the electron from an exciton can be attracted by the electronegative carbonyl oxygen and the exciton dissociation is promoted. In an applied external electric field, the created charge pairs can dissociate into free charge carriers, resulting in an increased photoconductivity extended into the visible spectral region.

In the case of diluted solutions of PDAF oligomer the optical transitions centered at 370 nm, typical of the fluorene group, are clearly visible as well as the vibronic peaks in the fluorescence emission spectrum centered at 420 nm. In the concentrated solutions and in the solid state the long-wavelength-shifted and featureless emission was observed. Moreover, the emission maximum was found to be dependent on the excitation wavelength showing the formation of the aggregates. The transfer of the excitons into the aggregate states was found to be effective and due to the prolonged lifetime of such trapped excitons the increased charge pair formation at high electric field was observed. On the other hand, the aggregates act as structural traps that hinder the charge carrier transport mostly in the low electric field limit resulting in the deterioration of the photoelectrical properties of the oligomer.

Acknowledgements: The financial support of the Grant Agency of the Czech Republic (grant No. 202/00/1152) is gratefully acknowledged.

PC87

VIBRATION-INDUCED ENERGY RELAXATION IN TWO-LEVEL SYSTEM

M. MENŠÍK, S. NEŠPŮREK

Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06 Prague 6, Czech Republic,

e-mail: mensik@imc.cas.cz

Energy transfer in a general two-level electronic system coupled to a vibrational harmonic mode interacting with a thermal bath is studied theoretically. Time dependences of a population of the higher electronic level (e.g. excited electronic state) are calculated for a long-time interval with respect to the vibrational period. The model assumes a general form of the off-diagonal elements (in the electronic basis) of the vibrational-electronic interaction, so that the cases for constant, linear or quadratic dependence with respect to the vibrational displacement is investigated.

In general, for all investigated cases of interaction the time dependences can be divided into three time intervals corresponding to a different physical behaviour.

For a short time, fast oscillations corresponding to a coherent energy exchange between electrons and vibrations appear. Their frequency w _e corresponds to the energy difference between electronic levels. Additionally, for the case of linear or quadratic coupling, the amplitude modulation of the oscillations with the frequency w _vib equal to that of vibration apears. If the Stokes shift increases than the amplitude modulation also increases and it can even smear out the time dependence given by the frequency w _e. For middle-time interval, almost an exponential decay of the higher electronic state population appears with the rate constant G proportional to the rate of vibrational relaxation and to the second power of the electron-vibrational coupling. If the dependence of the rate constant G on the ratio r of the energy difference of electronic levels and vibrational quantum is determined than for the small integer values r the peaks in the values of the rate constant G can be found.

For long-time interval, small values of the population of the higher electronic level appear even for sufficiently small temperatures and these values increase with the vibrational-electronic interaction. This effect can be found for all types of the investigated vibrational-electronic interactions.

PC88

THIN LAYERS OF TIO₂/POLYTHIOPHENE COMPOSITES USING ELECTRODEPOSITION METHOD

M. PAVLÍK^a, J. PFLEGER^a, N. HebesTreit^b, W. Plieth^b

^a Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, CZ-162 06 Prague 6, Czech Republic

^b Institute of Physical Chemistry and Electrochemistry, Dresden Technical University, Mommsenstr. 13, D-01062 Germany 

Electrodeposition has evolved recently to be a simple method for a fabrication of homogenous thin layers of insoluble materials, such as ceramics, with many possible applications. We adopted this method for the preparation of thin layers of insoluble composite nanoparticles composed of TiO₂ core and about 2 nm thick shell of polythiophene, prepared by oxidative polymerization of thiophene in the presence of FeCl₃, followed by the reduction in methanol. The reduced form of TiO₂-polythiophene composite material was deposited on the conductive surface from ultrasonically generated microdispersion. Varying of the dispersion media, applied voltage and the electrode arrangement made possible to control the quality and morphology of the films, as well as the polarity of the electrode on which the deposition proceeds. Typical voltage used for the deposition was in the order of hundreds volts (by distance between deposition and counter electrode about 1cm) and the deposition current in the order of milliamps. An improved quality and adhesion to the substrate was achieved by addition of a small amount of a polymer electrolyte to the deposition system. Compact semitransparent films deposited on ITO electrodes, suitable for photoelectrical measurements, were obtained within short deposition times (upto 20 seconds) in all cases.

The sandwich samples of the TiO₂-polythiophene with upper vacuum deposited Au electrode were characterized by the current-voltage characteristics in the dark and under illumination, and by the action spectra.of the photocurrent.

Acknowledgements: The financial support of the European Graduate School and of the Grant Agency of the Czech Republic (grant No. 202/00/1152) is gratefully acknowledged.

PC89

DEgradation and metastability in solution-processed and plasmatic polysilylanes

F. SchaueR^a, n. dokoupil^a, p. horváth^a, I. Kuřitka^a, m. otevřel^a, O. Salyk^a, M. weiter^a, s. nešpůrek^a,b, and P. schauer^c

^aFaculty of Chemistry, Brno University of Technology, Purkynova 118, 612 00 Brno, Czech Republic

^bInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06 Prague, Czech Republic

^cInstitute of Scientific Instruments of the Academy of Sciences of the Czech Republic, Královopolská 147, 612 64 Brno, Czech Republic

Polysilylenes, σ-conjugated polymers, constitute prospective materials for advanced display technologies. One of the principal obstacles for their application is their susceptibility to degradation and metastability with respect to UV radiation. The principal excitation is σ – σ^* of the Si chain, causing stretching or interrupting of the Si-Si chain and resulting in the defects that deteriorate both charge transport and photoluminescence properties.

The study deals with both poly[methyl(phenyl)silylene] (PMPSi) prepared by conventional polymerization [1] and deposited from solutions by spin-coating and by plasmatic polymerization in both radio-frequency and microwave discharges. The methods used for metastability studies were the transport measurements by post transit spectroscopy and optical measurements by standard steady-state and transient photoluminescence.

The transport measurements prove the existence of a metastable state with the energy of 0.55eV with respect to the transport band, generated by UV excitation [2]. The metastability explains the recovery of the degraded state by the controlled annealing with the activation energy of 0.6 eV. The degradation processes quench very effectively the luminescence in conventional PMPSi, but influence a little both the charge transport and luminescence properties in plasmatically prepared organosilicon. This effect is tentatively explained by existence of nanostructural one-dimensional islands in a rigid three dimensional covalently bonded Si network.

This work was supported by grants of Grant agency of Academy of Sciences of the Czech Republic No A1050901 and Grant agency of the Czech Republic No202/01/0518.

[1] P. Horvath, F. Schauer, I. Kuritka, O. Salyk, M. Weiter, N. Dokoupil, S. Nešpůrek, and V. Fidler, Chemical Monthly 132, 177 (2001).

[2] R. Handlíř, F. Schauer, S. Nešpůrek, I. Kuřitka, M. Weiter, and P. Schauer,
J. Non-Crystall. Solids (Hol.) 227-230, 669 (1998).

PC90

Controlled In-plane Alignment in Phthalocyanine Thin Films on Stepped Al₂O₃ Surfaces

J. O. Ossó,^1,2 F. Schreiber,^3,1 E. Barrena,¹ V. Kruppa,¹ H. Dosch,^1,3 M. Garriga,² M. I. Alonso,² F. Cerdeira^2,4

¹Max-Planck-Institut für Metallforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany

²Institut de Ciència de Materials de Barcelona, CSIC, 08193 Bellaterra, Spain

³Institut für Theoretische und Angewandte Physik, Universität Stuttgart, 70550 Stuttgart, Germany

⁴Instituto de Física "Gleb Wataghin", UNICAMP,13.083-970 Campinas S.P., Brazil

We report a detailed study of the growth, structure, and electronic properties of thin films of copper hexadecafluorophthalocyanine (F₁₆CuPc) on sapphire. These films show very good out-of-plane order and have X-ray rocking widths smaller than 0.02^°. If prepared under suitable conditions on A-plane sapphire substrates, the molecules align without significant azimuthal dispersion. Growth on MgO(001) and oxidized silicon wafers resulted in a comparable out-of-plane structure, but showed no azimuthal order. We find that the azimuthal alignment on sapphire is induced by the step edges along the c-axis of the sapphire, which serve as templates for the growth. The nucleation of film growth is investigated by AFM. The absence of multiple orientational domains can be exploited for efficient in-plane charge transport in the direction of maximum overlap of the p-orbitals.

PC91

SPACE-CHARGE LIMITED CONDUCTION IN ORGANIC LIGHT-EMITTING DIODES: THE ROLE OF CHARGE CARRIER MOBILITY AND TRAP STATES

WOLFGANG BRÜTTING, STEFAN BERLEB, ANTON G. MÜCKL

Experimental Physics II, University of Bayreuth, 95440 Bayreuth, Germany

The identification of the current-limiting mechanism in organic light-emitting diodes based on the prototype material tris(8-hydroxyquinoline) aluminium (Alq₃) has been the subject of controversial discussions between injection-limited behaviour, trap-limited conduction with a constant mobility and trap-free space charge limited conduction (SCLC) with a field-dependent mobility.

We demonstrate that the thickness dependence of the current at constant electric field provides a unique criterion to discriminate between the above mentioned limiting cases. The underlying transport equations are solved numerically assuming space-charge limited conduction with a Poole-Frenkel type charge carrier mobility: and trap states distributed in energy. By comparing experimental results of thickness and temperature dependent current-voltage characteristics of Alq₃ electron-only devices with numerical simulations, the field and temperature dependence of the mobility and the trap distribution is obtained. Using impedance spectroscopy under SCLC conditions allows to analyse the dispersive nature of charge carrier transport in this material. From the observed temperature independence of the dispersion parameter the dominance of positional disorder is concluded.

PC92

FREQUENCY ANALYSIS OF DIFFUSION IN 1 D SYSTEMS WITH ENERGY AND SPATIAL DISORDER

A. PITARCH, G. GARCIA-BELMONTE, J. BISQUERT

Departament de Ciències Experimentals, Universitat Jaume I, 12080 Castelló, Spain

We have analyzed the frequency dependent diffusivity related to diffusive transport of mobile carriers by hopping in a disordered environment composed of varying energy barriers. We develop a simple approach based on the solution of the master equation with a sinusoidal perturbation. This method extends the well known result of the steady state case, , to the frequency domain. The results of our calculations are in agreement with the approximate analytical solutions of the CTRW and EMA methods. We are able to determine the onset of frequency-dependent diffusivity in terms of probabilities of highest energy barriers.

PC93

Quenching of Exciplex and Charge -Transfer Complex Fluorescence of Poly(N-vinylcarbazole)-benzanthrone System

R.M. Siegoczyński and W. Ejchart

Abstract not available