Poly p-phenylene vinylenes PPVs

Poly(phenylene vinylene) (PPV) is another valuable conjugated polymer, as the synthetic process of PPV is simple and low cost. PPV possesses excellent photoluminescent (PL) and electroluminescent (EL) properties, as well as photovoltaic (PV) and nonlinear optical properties [57]. These properties have led to its being used in broad applications, in such areas as light-emitting diodes (LEDs) and flat-panel displays and photonics applications such as wave-guiding and all-optical switching. 

PPV nanofibers that retain their photoluminescent properties were fabricated by electrospinning PPV precursor solution in solvent mixtures of ethanoFwater [57-59]. The luminescent nanofibers were obtained by electrospinning a solution of PMO-PPV, Eu(ODBM)3phen and PMMA. The electrospun fibers, with diameters ranging from 70 nm to 200 nm and having a parallel orientation, show strong green and red 

Poly[2-methoxy-5-(2 -ethyl-hexyloxy)-l,4-phenylene vinylene] (MEH-PPV) is an excellent conjugated polymer and broadly used in polymer photoelectron devices, but is difficult to electronspin directly. In the work by Zhao et al, core-shell structured nanofibers were fabricated by coaxial electrospinning MEH-PPV (shell) in chlorobenzene and PVP (core) in 1,2-dichloroethane [64]. MEH-PPV was soluble in the above two solvents, which prevented the precipitation of MEH-PPV and enhanced the adhering action between the two polymers in the coaxial electrospinning process. It should be noted that this is an unusual example of core-shell nanofibers where (a nonprocessable) PPV was spun as the shell and not in the core. These uniform core/shell PVP/MEH-PPV nanofibers with a highly fluorescent property can have potential applications in the fabrication of polymer nanophotoelectron devices. 

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FIGURE 5.4 Chemical structures of photo- and electroluminescent polymers employed for polarized LEDs poly(2-methoxy-5-(2 -ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) poly[2,5-dioctyloxy-l, 4-diethynyl-phenylene-a/t-2,5,-bis(2 -ethylhexyloxy)-l,4-phenylene] (EHO-OPPE) poly(p-phenylene), PPP poly(3-(4-octylphenyl)-2,2 -bithiophene), PTOPT poly(p-phenylene vinylene), PPV poly(3-alkylthio-phene vinylene), P3AT Acetoxy-PPY PPV-polyester, poly(9,9-dialkyl fluorene), PF. 

Attempts to dope organic semiconductors have been made very early in the field, motivated by the prospect of possibly reaching metallic conductivities [108, 109]. These synthetic metals, however, have not been realized. While p-type doping could be obtained, for example, with iodine gases for poly-p-phenylene vinylene (PPV) derivatives, and n-type doping was demonstrated with sodium for a cyano-derivative of PPV, the doping levels obtained were not stable with time. The dopant molecules readily diffused into the organic semiconductor, yet also out of it. Due to the lack of stability, these approaches were not suitable for commercial applications. 

During the past three years we have been studying the chemical (SbCl5) oxidation of well-characterized oligomers of polyacetylene, poly[p-phenylene vinylene] (PPV) and poly[2,5-thienylene vinylene] (PTV) in order to determine how polaron and bipolaron states can be preferentially formed and stabilized. 

The materials (metals and conjugated polymers) that are used in LED applications were introduced in the previous chapter. The polymer is a semiconductor with a band gap of 2-3 eV. The most commonly used polymers in LEDs today are derivatives of poly(p-phenylene-vinylene) (PPV), poly(p-phenylene) (PPP), and polythiophene (PT). These polymers are soluble and therefore relatively easy to process. The most common LED device layout is a three layer component consisting of a metallic contact, typically indium tin oxide (ITO), on a glass substrate, a polymer film r- 1000 A thick), and an evaporated metal contact4. Electric contact to an external voltage supply is made with the two metallic layers on either side of the polymer. 

The work on Alq3 and other small 7r-conjugated molecules that followed shortly thereafter13 14 demonstrated that multilayer OLEDs could be fabricated simply by thermal evaporation of these molecules. In 1990 Friend and coworkers described the first PLED,15 in which the luminescent poly(p-phenylene vinylene) (PPV)... 

The chemical structures of two poly(p-phenylene vinylene) (PPV) derivatives, one a copolymer formed by a random succession of phenylene vinylene and ether groups and the other characterized by a pendant side chain containing ether groups, were characterized by solid-state NMR and other techniques. ... 

Although early examples of OLEDs included polymers, specifically poly (p-phenylene vinylene) (PPV), as the emissivematerial [61 ], conjugated oligomers can also be useful emitters as well as energy harvesters. Oligomers offer advantages over their polymeric parents such as ease of synthesis and func-... 

Poly(p-phenylene vinylene) (PPV) and its analogues exhibit high conductivities (1-10 S/cm) but can only... 

Figure 7.2 Structures of polymers reviewed in this chapter (a) poly(3-alkylthiophenes) (P3ATs) (b) poly(p-phenylene vinylene) (PPV) and 2,5-dialkoxy PPV (c) CN-PPV (d) 2.5-dialkoxy poly(p-phenylene ethynylenes) (PPHs) (e) poly(3-hexyl thiophene cthynylenes) (P3ATs) (f) poly(p-di ethynylene phenylene-p-di phenylene vinylene) (PDEPDPV) and CN-PDEPDPV (g) poly(/>-phenylene ethynylene anilines) (PPEAs).

Poly(p-phenylene vinylene) (PPV) is a conjugated polymer, which becomes conductive by the addition of electron donors or acceptors [114, 115], Several methods have been reported for the synthesis of PPV [3, 4, 6], Direct chemical polymerization, which was used in the first attempt of synthesizing PPV, gave a product in the form of an insoluble powder that limited the use of the polymer in many applications [116], The most popular method for the preparation of PPV is base-induced polymerization of sul-fonium salt monomer in aqueous solution [114-118], In this method, PPV films are obtained from the precursor polymer after thermal elimination of the sulfonium groups. PPV has also been prepared electrochemically by reducing p-xylene-bis-(triphenylphosphonium). Two approaches are generally used for the synthesis of PPVs the Wessling... 

With this method, single poly(p-phenylene vinylene) (PPV), PANI, and PPY nanowires have been synthesized and very narrow CPNWs with diameters as small as 5 nm have been demonstrated using DNA templates [60-63],... 

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