Poly p-phenylenevinylene

In the following sections, results from various photoelectron spectroscopy studies of poly(p-phenylenevinylene), polythiophene, and polyaniline, and their interaction with different metals will be discussed. The intention is not to cover the whole existing literature, but still give a relatively extensive overview, and, where appropriate, give references for further reading. 

5 Electronic Structure of Surfaces and Interfaces in Conjugated Polymers 

In the many reports on photoelectron spectroscopy, studies on the interface formation between PPVs and metals, focus mainly on the two most commonly used top electrode metals in polymer light emitting device structures, namely aluminum [55-62] and calcium [62-67]. Other metals studied include chromium [55, 68], gold [69], nickel [69], sodium [70, 71], and rubidium [72]. For the cases of nickel, gold, and chromium deposited on top of the polymer surfaces, interactions with the polymers are reported [55, 68]. In the case of the interface between PPV on top of metallic chromium, however, no interaction with the polymer was detected [55]. The results concerning the interaction between chromium and PPV indicates two different effects, namely the polymer-on-metal versus the metal-on-polymer interface formation. Next, the PPV interface formation with aluminum and calcium will be discussed in more detail. 

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Other polymers ia this category iaclude CJ-conjugated polygermylenes (20) and TT-conjugated poly acetylene, polythiophene, and poly(p-phenylenevinylene). The photoconductivity of many TT-conjugated polymers can be enhanced by dopiag with fuUerenes (21). 

This review has shown that the analogy between P=C and C=C bonds can indeed be extended to polymer chemistry. Two of the most common uses for C=C bonds in polymer science have successfully been applied to P=C bonds. In particular, the addition polymerization of phosphaalkenes affords functional poly(methylenephosphine)s the first examples of macromolecules with alternating phosphorus and carbon atoms. The chemical functionality of the phosphine center may lead to applications in areas such as polymer-supported catalysis. In addition, the first n-conjugated phosphorus analogs of poly(p-phenylenevinylene) have been prepared. Comparison of the electronic properties of the polymers with molecular model compounds is consistent with some degree of n-conjugation in the polymer backbone. 

The introduction of bulky side chains that contain adamantyl groups to poly(p-phenylenevinylene) (PPV), a semiconducting conjugated polymer, decreases the number of interchain interactions. This action will reduce the aggregation quenching and polymer photoluminescence properties would be improved [93]. 

DM Johansson, G Srdanov, G Yu, M Theander, O Inganas, and MR Andersson, Synthesis and characterization of highly soluble phenyl-substituted poly(p-phenylenevinylenes), Macromolecules, 33 2525-2529, 2000. 

AR Brown, K Pichler, NC Greenham, DDC Bradley, RH Friend, and AB Holmes, Optical spectroscopy of triplet excitons and charged excitations in poly(p-phenylenevinylene) light-emitting diodes, Chem. Phys. Lett., 210 61-66, 1993. 

DuPont is an active player in OLED technology. Polymers used in devices as emitting materials are poly(p-phenylenevinylene), poly(arylenevinylene)s, poly(p-phenylene), poly(arylene)s, polyquinolines, and polyfluorenes. In some cases, an anionic surfactant such as lithium nonylphenoxy ether sulfate was added to the above-mentioned polymeric emitters... 

Among the n-conjugated polymers, poly(p-phenylenevinylene)s (PPVs) have attracted particular attention since the 1990 report of Friend et al. on... 

Di(dibromomethyl)benzene is reduced at a mercury cathode to yield the poly(p-phenylenevinylene) 41. The reaction proceeds through a brominated poly-... 

The dibromo- (and diiodo-) stilbenes ate potentially useful monomers tor the synthesis of poly(p-phenylenevinylenes) via poly-Heck or poly-Suzuki coupling reactions. ... 

Multiple Heck reactions have also been applied in a number of ways to prepare polymers (Scheme 40). One-dimensionally 7r-conjugated polymers are attractive materials because of their optical and electrical properties resulting from 7r-electron delocalization along their main chains. Among these, poly(p-phenylenevinylene) (PPV) shows high electrical conductivity, large non-linear optical responses, and electroluminescent activity. One approach... 

The ROMP of [2.2]paracyclophane-l,9-diene (128) yields poly(p-phenylenevinylene) (129) as an insoluble yellow fluorescent powder. Soluble copolymers can be made by the ROMP of 128 in the presence of an excess of cyclopentene387, cycloocta-1,5-diene388 or cyclooctene389. The UV/vis absorption spectra of the copolymers with cyclooctene show separate peaks for sequences of one, two and three p-phenylene-vinylene units at 290, 345 and about 390 nm respectively, with a Bernoullian distribution. The formation of the odd members of this series must involve dissection of the two halves of the original monomer units by secondary metathesis reactions. 

Such design concepts were first reported utilizing 2,2 -bithiazole and 2,2 -bi-pyridine units, respectively, as postpolymerization metal coordination sites [349, 350]. Subsequently, a poly(p-phenylenevinylene)-based polymer 69 containing ionic ruthenium centers bound to bipyridyl (BPY) units incorporated into the polymer backbone was reported. This system, depicted in Scheme 68, exhibits enhanced photoconductivity relative to the parent organic polymer [351] (Yu). 

In the soluble precursor route, a suitable precursor is synthesized which can be cast into a device structure (i.e., film) by using solution processing. Then it can be converted into the final nonlinear structure upon subsequent treatment (such as heat treatment). This approach has been used for poly-p-phenylenevinylene (PPV) as shown below (32) ... 

IDW Samuel, G Rumbles, CJ Collison, SC Moratti, AB Holmes. Intra- and inter-molecular photoexcitations in a cyano-substituted poly(p-phenylenevinylene). Chem Phys 227 1,2, 75-82, 1998. 

By introducing long alkyl side chains into the poly(p-phenylenevinylene) (PPV) backbones and to the amino groups on the NLO chromophores, a low-7), polymer X (Scheme 8) containing ruthenium complexes and a conjugated system is... 

Five different polymeric species containing rhenium(I) tricarbonyl complexes are shown in Fig. 17. Polymer A contained Re(CO)3Cl units attached to a dipyridyphenazine ligand [79]. The polymer components were varied from x = 0.1 and y = 0.9 to x = 1 and y = 0 with the latter variation providing the most evidence for the presence of the rhenium complex. A shoulder located at ca. 550-600 nm was attributed to the characteristic MLCT optical transition for the rhenium complex. The photoluminescence spectrum gave a continuous decrease of emission from the poly(p-phenylenevinylene) back-... 

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