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Über dieses Buch

The articles in this book summarize the work presented at the final workshop of the COST (European Cooperation in the Field of Scientific and Technical Research) Action on Molecular Materials and Functional Polymers for Advanced Devices, which was held in June 2000 in Patras, Greece. The collection gives an excellent overview of the state-of-the-art in this field and the progress made by the coordinated research projects. The results range over the synthesis, physical properties, and applications of molecular materials (nanotubes, fullerenes, phthalocyanines), inorganic and inorganic-organic hybrid materials, and functional polymers (electronic conduction, photoluminiscence, optical storage, photovoltaic devices).



Phthalocyanines and Phthalocyanine Analogues: The Quest for Applicable Optical Properties

The central subject of this article is the description of the current work of the authors in the context of the Cost Action 518, project DE-1, and the Phthalocyanines Research Training Network, both financed by the European Community. The aim of the above projects is the design, synthesis, and structural and physical characterization of molecular and polymeric materials based on phthalocyanine derivatives with particular optical properties, as well as the study of their technological applications in the sensors field.
Christian G. Claessens, Werner J. Blau, Michael Cook, Michael Hanack, Roeland J. M. Nolte, Tomás Torres, Dieter Wöhrle

Inorganic Clusters in Organic Polymers and the Use of Polyfunctional Inorganic Compounds as Polymerization Initiators

Silicon oxide or metal oxide clusters or small particles with polymerizable organic groups covalently bonded to their surface can be copolymerized with organic monomers by various polymerization techniques. Whereas the preparation and properties of the polymers reinforced by R 8Si8O12 have already been well investigated, analogous materials with incorporated transition metal oxide clusters are only beginning to show their potential as an interesting new class of inorganic-organic hybrid polymers. In the second part of the article, approaches are reviewed in which the inorganic building block serves as an initiator for polymerization reactions. This results in materials in which the organic polymer is grafted from an inorganic core. Most work has been done with surface-modified silica particles. Free radical polymerizations and atom transfer radical polymerizations with macroinitiators are summarized. The latter method results in polymeric particles in which an inorganic core is surrounded by an organic polymer shell. A new approach is the use of polyfunctional inorganic molecules or molecular clusters as initiators.
Kickelbick Guido, Schubert Ulrich

Recent Studies on Super-Hydrophobic Films

Films whose water contact angle is higher than 150° have been the subject of great interest and enthusiastic study in recent years. These films, which are called super-hydrophobic, are fabricated by combining appropriate surface roughness with surfaces of low surface energy. Here we briefly review the fundamental theories on the wettability of a hydrophobic rough solid surface, together with recent works on the processing and properties of super-hydrophobic films. Though the practical application of these films is still limited, the obstacles to application are gradually being surmounted, providing a great opportunity for the development of various industrial products.
Akira Nakajima, Kazuhito Hashimoto, Toshiya Watanabe

The Azobenzene Optical Storage Puzzle — Demands on the Polymer Scaffold?

The basic mechanism of optical information storage utilizing the azobenzene photoaddressable moiety will briefly be introduced. A synthetically flexible polyester matrix covalently integrating cyanoazobenzene in regularly spaced side chains is particularly well suited for holographic storage. Notable figures of merits of thin film materials of liquid crystalline polyesters are: response time to laser light in the order of ns, storage capacity of 5000 lines/mm, high permanent (more than eight years) diffraction efficiency in the order of 50% or higher, and erasability. The implications of the nature of the main chain on polyester morphology and on the permanency of the induced anisotropy are discussed. Arguments for the design and methods of preparation of other very different polymer scaffolds supporting the cyanoazobenzene are elucidated. Whereas oligopeptides invariably form amorphous materials, both copolymethacrylates and dendritic or hyperbranched polyesters provide some materials that exhibit liquid crystallinity. However, none of these other scaffolds offer materials that allow long-lasting anisotropy to be laser light induced.
Søren Hvilsted, P. S. Ramanujam

Nanotube Content in Arc Generated Carbon Powder

A novel experimental technique for the separation of nanotubes from other unwanted carbon species in arc generated carbon soot is described. A conjugated polymer was used to bind to nanotubes in solution. The resultant hybrid was soluble, whereas extraneous carbon material formed a sediment at the bottom of the sample bottle. The process was monitored using electron paramagnetic resonance (EPR) spectroscopy showing that 63% of nanotubes were kept in solution and 98.1% of impurities were rejected. This non-destructive purification allowed the calculation of the nanotube content in the carbon soot using EPR and thermogravimetric analysis (TGA). The measurement of nanotube content gave a purity value of 34% for the soot used in this study; this is compatible with estimates from electron microscopic determinations.
Jonathan N. Coleman, Diarmuid F. O’Brien, Brendan McCarthy, Robert C. Barklie, Werner J. Blau

Novel Functional Fullerene Materials: Fullerenes as Energy Acceptors

Fullerene derivatives exhibit absorption throughout the UV/Vis region up to 750nm. This feature is important for easy excitation. Once excited, fullerenes may become both electron and energy acceptors. The distinction between these two pathways depends strongly on the partner involved (donor) and on the conditions employed (solvent, etc.).
Konstantinos Kordatos, Tatiana Da Ros, Maurizio Prato, Chuping Luo, Dirk Guidi

A Phenyl α-Nitronyl Nitroxide with a Forced Chiral Conformation

A new phenyl α-nitronyl nitroxide bearing a hydroxyl group at position 2 of the aromatic ring and a chiral methyl lactate substituent at position 5 has been synthesized with the aim of combining the magnetic properties of this kind of radical with the optical properties endowed by the chiral group. The optically active compound forms intramolecular hydrogen bonds between the OH group and one of the NO groups and shows a large torsion angle between the two rings when compared with similar radicals with no substituent in this position. Therefore, the optical properties are distinct. The optical and magnetic properties of the new radical in both solution and solid state are presented.
Maria Minguet, David B. Amabilino, Klaus Wurst, Jaume Veciana

Thin Film Counterelectrodes with High Li Charge Capacity for Electrochromic Windows

Ce-V mixed oxide films have been deposited by RF sputtering with the aim of increasing the Li charge capacity of counter electrodes in smart windows. Such mixed oxides have shown high transmittance and optical passivity in the visible region. After electrode pre-conditioning by cyclic voltammetry, a good electrochemical reversibility in LiC104 — propylene carbonate electrolyte was observed, and large Li-charge capacity under galvanostatic charging (up to 50 mC · cm−2) has been measured. The electrode charge capacity decreased after prolonged insertion-deinsertion cycles, whereas the photoptic transmittance remained about constant. After 800 cycles the Li-charge capacity decreased to 40mC · cm−2. The Li diffusion coefficient inside the films measured by electrochemical impedance and by galvanostatic titration ranged from 10−11 cm2 · s−1 to 10−13 cm2 · s−2. We observed that the Li charge capacity of the film electrodes is a function of the film deposition conditions, because it increased with the vanadium oxide concentration in the target and with the oxygen content in the sputtering atmosphere.
Franco Varsano, Francesca Decker, Enrico Masetti

Studies on Hybrid Organic/Inorganic Nanocomposite Gels Using Photoluminescence Techniques

Transparent nanocomposite gels made of hybrid organic/inorganic polymers, synthesized through the sol-gel method, composed of poly-(ethylene oxide) or poly-(propylene oxide) chains, and grafted on silica through urea bridges, have been studied by steady-state and time-resolved photoluminescence techniques. These nanocomposite materials consist of two distinguished subphases, an organic and an inorganic one. The volume fraction of the organic (polyether) subphase is larger than that of the inorganic (silica) subphase, and it increases with increasing polyether chain size. The condensation of the silica subphase provides luminescent entities emitting light by electron-hole recombination on delocalized states associated with the active chemical species of the urea bridges. Materials with smaller polyether chains are more luminescent than such with longer polyether chains. Divalent or trivalent cations introduced into these materials enhance the luminescence intensity by solubilization close to the silica cluster surface and thus by decreasing surface defects and the ensuing quenching mechanism.
Vlasoula Bekiari, Elias Stathatos, Panagiotis Lianos, Urska L. Stangar, Boris Orel, Patrick Judeinstein

Organic-Inorganic Sol-Gel Hybrids with Ionic Properties

A hybrid silicon precursor (ICS-PPG) obtained by reaction of 3-isocyanatopropyltriethoxy silane with poly-(propyleneglycol)-bis-(2-aminopropyl ether) was recognized as a potential host for various salts and molecular species. It has been used for electrochromic, gasochromic, photovoltaic, and fuel cell applications. This focuses on proton conducting gels (PWA/ICS-PPG, SiWA/ICS-PPG, and W-PTA/ICS-PPG) obtained after the incorporation of polyoxometalates in the ICS-PPG host. IR spectroscopic measurements are used to reveal the entrapment, the aggregation, and the interactions of W-PTA, PWA, or SiWA with the sol-gel derived network. The proton conductivity of the composites, measured using impedance spectroscopy, increases with increasing concentration of the polyoxometalates from 10−6 to 10−3 S/cm.
Urška L. Štangar, Boris Orel, Neva Grošelj, Patrick Judeinstein, Franco Decker, Panagiotis Lianos

Excitonic Bands in the Spectra of Some Organic-Inorganic Hybrid Compounds Based on Metal Halide Units

The optical absorption, photoluminescence, and photoconductivity spectra of some compounds of the formulas [R(CH2)nNH3] x M y X z , [R(CH2)nNH(CH3)2] x M y X z , [R(CH2)nSC(NH2)2] x M y X z , and [R(CH2)nSeC(NH2)2] x M y X z (R = organic residue; M = Bi(III), Pb(II), Sn(II), Cu(I), Ag(I) etc; X= I, Br, Cl; n, x, y, z = 0, 1, 2, 3, …) are briefly reviewed, and some new results are reported. The position, intensity, and shape of the excitonic bands depend on the dimensionality and size of the inorganic network as well as on the nature of the M, X, R, and onium moieties.
George C. Papavassiliou, George A. Mousdis, Ioannis B. Koutselas

Highly Regioregular Poly-3-alkylthiophenes: Influence of the Structure on Photoluminescence

A class of regioregular poly-3-alkylthiophenes was synthesized via a new and simple synthetic procedure. These polymers exhibit a regioregularity as high as 95–100% and show different thermal behaviour depending on the length of the side chain. The high conjugation length reached is responsible for a red-orange emission with photoluminescence (PL) quantum efficiencies of about 45% in solution. The study of the PL of spin coated films at different temperatures allows to correlate the PL spectra with the structure of the polymers as detected by XRD.
Alberto Bolognesi, Chiara Botta, William Porzio

The Role of Interfaces in Photovoltaic Devices

Organic opto-electronic devices comprise one or more organic layers and the electrodes. The interfaces between these very different components play a crucial role to the performance of the devices. In donor-acceptor composites for photovoltaics, the electronic processes occurring at the interface will benefit from a particular interface morphology on the 10–100 nanometer level; this is demonstrated for composites of oligophenylenevinylene and C60. Phase separation on such a scale may be achieved naturally in diblock copolymers. The synthesis of an OPV — C60 diblock copolymer is described.
Paul F. van Hutten, Georges Hadziioannou

Peculiarities of the Interaction of Short Oligonucleotides with Supported Lipid Films and Langmuir Monolayers

The method of electrostriction was applied to supported bilayer lipid membranes (sBLM) and Langmuir monolayers with the aim to study the peculiarities of the interaction of short oligonucleotides with lipid films and of the duplex formation between complementary oligonucleotides. The bilayer lipid membranes (sBLM) were formed on an agar support, whereas Langmuir monolayers were generated on the air-water interface. As an oligonucleotide, the 15-mer 5’-cholesterolphosphoryl-dt15 (CHpdTIS) was synthesized. We could show that the interaction of CHpdT15 with sBLM resulted in a considerable increase of the elasticity modulus perpendicular to the membrane plane (E⊥) and an increase of the surface potential. Interaction of complementary oligodeoxyadenylate (dA15) with sBLM modified by CHpdT15 resulted in a slight increase of the surface potential whereas E⊥ slightly decreased. CHpdT15 forms monomolecular layers on the air/water interface. Interaction of dA15 with such monolayers resulted in an increase of the surface pressure, probably due to an increase of the surface charge of the monolayer; similar effects were observed for lipid monolayers modified by CHpdT15 Prospects of using such interactions for detecting DNA hybridization are discussed.
Tibor Hianik, Martin Fajkus, Pavol Tomcik, Ivan Rosenberg, Pavol Kois, Julius Cirak, Joseph Wang

The Photophysics of Thin Polymer Films of Poly-(meta-Phenylene-Co-2,5-Dioctoxy-para-Phenylenevinylene)

We have investigated the effect of film preparation procedures on the photoluminescence efficiency of the luminescent co-polymer poly-(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV). The photoluminescence efficiency of PmPV films improved by up to 50%; when the solution was degassed by bubbling argon gas through it prior to spin casting in an inert atmosphere and baking under vacuum. Photoinduced absorption and doping measurements show that this preparation method reduces polaron photogeneration, which reduces the photoluminescence (PL) yield through exciton quenching and excited state absorption. It is proposed that this sample preparation method increases interchain separation, reducing the formation of polarons and non-radiative quenching routes, thus resulting in increased PL efficiency.
Stephen M. Lipson, Ashley J. Cadby, Paul A. Lane, Diarmuid F. O’Brien, Anna Drury, Donald D. C. Bradley, Werner J. Blau

Visible Photoluminescence in Polysilanes

The photoluminescence spectrum of poly-(methyl-(phenyl)-silanediyl) shows a strong narrow peak in the UV region which is of excitonic nature and related to σ*-σ transitions. The broad emission peak in the visible region is related to polymer branching, charge transfer transitions, and defect electronic states (backbone scission). Chemical substitution of the Si backbone with л-conjugated side groups allows to generate photoluminescence also in the visible region.
Stanislav Nešpůrek, František Schauer, Andrey Kadashchuk

Examination of the Spatial Distribution of Dyes and Polymers in Thin Films by Two-Photon Microscopy

Two-photon absorption induced fluorescence microscopy was used as a tool for the examination of the spatial distribution of a thin dye film. The two-photon absorption induced fluorescence signal is essentially the same as that produced by excitation with a single photon of equivalent energy. When femtosecond pulses are focused into a sample there is an intrinsic spatial selectivity of the two-photon emission signal, since it is dependent upon the square of the light intensity. This has tremendous implications in fluorescence microscopy. Since two-photon absorption is confined in a small region at the focal waist of an objective lens, photodamage and photobleaching of the sample are significantly reduced. In addition, the two-photon signal has inherent z-axis spatial resolution, which facilitates the construction of 3-D images. In the present work an application of this technique to a thin film of a dye is presented. The method can generally be applied to thin films made from photonic polymers.
Ioannis Polyzos, Georgios Tsigaridas, Mihalis Fakis, John Parthenios, Anastassios Fragos, Vassilis Giannetas, Peter Persephonis, John Mikroyannidis

Luminescence in Organic Silicons Prepared from Organic Precursors in Plasma Discharges

The photoluminescence of plasma-prepared polysilanes during the change from linear ID Si chains to an amorphous 3D Si network was studied. The excitonic absorption band with a maximum at 353 nm in ID Si experiences a blue shift and broadening upon introduction of branching and networking defects. With the gradual transition from ID to 3D structure, an extensive redistribution of oscillator intensity along the absorption edge, accompanied by a decrease of the resolution of the σ*-σ band, was observed. In the short wavelength region of the excitation spectra there is an enormous increase of excitonic emission at 328 nm. This effect is tentatively attributed to the excitation of the phenyl group or to the phenyl-silicon bond as confirmed by effusion spectra of the phenyl species.
Pavel Horváth, František Schauer, Ivo Kuřitka, Ota Salyk, Martin Weiter, Norbert Dokoupil, Stanislav Nešpůrek, Vlastimil Fidler

UV-Induced Electrical and Optical Changes in PVC Blends

2-Chloro-polyaniline (2-C1-PANI) in its non-conducting (emeraldine base, EB) form, prepared by a chemical route, was dissolved together with poly-(vinylchloride) (PVC) in THF for casting into thin (10–50 μm) films. Upon exposure to UV radiation, the electrical conductivity of these films increased by more than 4 orders of magnitude (from 10−6 to 10−2 S/cm). This is attributed to the dehydrochlorination of PVC by exposure to energetic photons and subsequent doping of 2-C1-PANI (i.e. conversion to emeraldine salt, ES) by in situ created HC1. The doped films could be returned to their undoped form by exposure to NH3 vapours. The UV-induced doping/NH3 undoping cycles could be repeated several times. Various spectroscopic techniques were employed to follow the changes in the films upon exposure to UV radiation. The same photo-dehydrochlorination process has also been utilized for optical and/or lithographic purposes by preparing PVC blends containing methyl violet, and acid-base indicator dye. The photo-dehydrochlorination can be effectively sensitized by incorporating hydroquinone into the PVC blends containing methyl violet.
Sefik Suzer, Ozgur Birer, Adnan U. Sevil, Olgun Guven


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