Reductive Photopatterning of Phenylene-Vinylene-Based Polymers
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Reductive photopatterning of phenylene-vinylene-based polymers T. Kavc1, G. Langer1, W. Kern1 *), A. Ruplitsch1, K. Mahler1, F. Stelzer1, G. Hayn1, R. Saf1, E.J.W. List2, E. Zojer2, M. T. Ahmed2 # , A. Pogantsch2, K.F. Iskra3, T. Neger3, H.-H. Hörhold4, H. Tillmann4, G. Kranzelbinder5, E. Toussaere5, G. Jakopic6 1 Institute for Chemistry and Technology of Organic Materials, Graz University of Technology, Graz, Austria 2 Institute of Solid State Physics, Graz University of Technology, Graz, Austria 3 Institute for Experimental Physics, Graz University of Technology, Graz, Austria 4 Institute of Organic Chemistry and Macromolecular Chemistry, University of Jena, Germany 5 Ecole Normale Superieure de Cachan LPQM, Cachan, France 6 Joanneum Institute of Nanostructured Materials and Photonics, Weiz, Austria # Affiliation: Mansoura University, Mansoura 35516, Egypt *) To whom all correspondence should be adressed
ABSTRACT Photochemical methods were developed to obtain a variation of the refractive index in aromatic polymer surfaces and a change in the photoluminescence characteristics of phenylenevinylene-based polymers. Films of aromatic polymers, among them polystyrene (PS), poly(2vinylnaphthalene) (PVN) and derivatives of poly(p-phenylene-vinylene) (PPV) were UV irradiated in the presence of gaseous hydrazine (N2H4). The photoreaction led to a strong reduction of the refractive index of the polymers due to a hydrogenation of the aromatic units. In the case of PPV, we observed reductive photobleaching. This new technique was employed to produce photogenerated patterns in PPV. The results are compared to oxidative bleaching.
INTRODUCTION Several patterning strategies have been developed for conjugated polymers, e.g. to obtain pixelated LEDs for multicolored displays. Besides conventional photolithography, direct patterning strategies for conjugated polymers are of immediate interest. Examples of current techniques are laser ablation [1], ink-jet [2] and ion-beam deposition techniques, controlled vapour deposition [3], modified scanning force microscopy [4] and local dye diffusion [5]. UV irradiation under oxygen (i. e. photooxidative patterning) is an emerging technique to change the emissive properties of conjugated polymers [6-10]. Only recently, luminescent patterns in LED devices have been produced by oxidative bleaching [11-12]. However, detailed informations on the reaction mechanisms and photooxidation products (e.g. ketones which act as quenching centers) are seldom available. In the present work it is shown that reductive bleaching of conjugated polymers via UV illumination under gaseous hydrazine (N2H4) is an interesting alternative for patterning of PPV derivatives.
AA11.3.1/BB11.3.1
EXPERIMENTAL DETAILS Films of polystyrene (PS), poly(2-vinylnaphthalene) (PVN) and MEH-PPV were cast onto Si and CaF2 plates using a spincoater. The films were placed in an irradiation chamber equipped with quartz windows. Hydrazine hydrate (N2H4.H2O) was dehydrated following a literature method [13], placed in a thermostatted
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