Poly para-phenylene

Figure 8.12. A conjugated chain in poly(acetylene). (a) changes to (b) when a charge passes along the backbone of the molecule, (c) and (d) show chains of poly(acetylene) and poly(para phenylene) respectively, each containing solitons (after Windle 1996).

Concerning the nature of electronic traps for this class of ladder polymers, we would like to recall the experimental facts. On comparing the results of LPPP to those of poly(para-phenylene vinylene) (PPV) [38] it must be noted that the appearance of the maximum current at 167 K, for heating rates between 0.06 K/s and 0.25 K/s, can be attributed to monomolecular kinetics with non-retrapping traps [26]. In PPV the density of trap states is evaluated on the basis of a multiple trapping model [38], leading to a trap density which is comparable to the density of monomer units and very low mobilities of 10-8 cm2 V-1 s l. These values for PPV have to be compared to trap densities of 0.0002 and 0.00003 traps per monomer unit in the LPPP. As a consequence of the low trap densities, high mobility values of 0.1 cm2 V-1 s-1 for the LPPPs are obtained [39]. 

S. Tasch, A. Niko, G. Leising, U. Scherf, Highly efficient electroluminescence of new wide band gap ladder-type poly(para-phenylenes), AppL Phys. Lett. 1996, 68, 1090. 

Several attempts to use otganic polymeric semiconductors as the active component in photovoltaic devices have been reported during the last two decades. Interest in the photovoltaic properties of conjugated polymers like polyacelylcne, various derivatives of polythiophenes and poly(para-phenylene vinylene)s arose from... 

W. Graupner, G. Ccrullo, M. Lanzatti, M. Nisoli, E.J. W. List, G. Leising, S. De Silvcstri, Direct observation of ultrafast field-induced charge generation in ladder-type poly(para-phenylene). Phys. Rev. Lett. 1998, 81. 3259. 

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... 

Poly f p-oxybenzoyl-co-p-phenylene isophthalate]), 113-114 Poly(2,2 -oxydiethylene adipate), 29 Polyoxymethylene glycol, aqueous, 377 Poly(oxytetramethylene) (PTMO), 53 Poly (p-pheny lene). See also Poly(para-phenylene)s dendronized, 520-521 synthesis of, 491-494 synthesis of water-soluble, 493 Poly(phenylene ether sulfone) chains,... 

Poly(phenyleneethynylene)s, 482 optically active, 516-517 synthesis of, 496-500, 502 Poly(m-phenylene isophthalamide), 136 synthesis of, 185-186 Poly(l,4-phenylene terephthalate) liquid crystalline polymers, 51 Poly(para-phenylene)s, 472. See also Poly (p -pheny lene)... 

An important challenge in the design of novel conjugated polymers is the synthesis of materials with tailor-made solid-state electronic properties. This section outlines the synthesis of the most significant classes of poly(para-phenylenevinylene)s (PPVs), poly(para-phenylene)s (PPPs), and related structures. Furthermore, this review demonstrates that the chromophoric and electronic properties of conjugated rr-systems are sensitive to their molecular and supra-molecular architecture. 

Keywords Poly(para-phenylene)s, Poly(para-phenylenevinylene)s, Oligomers, Photoluminescence, Electroluminescence, Light emitting diodes. 

Ladder-Type Oligo- and Poly(para-phenylene)s.177... 

Ladder-Type Poly(para-phenylene-czs-vinylene)s.216... 

The requirements outlined above represent a considerable challenge for polymer synthesis. This article describes an appealing development, based on two central substance-classes of conjugated polymers, poly(para-phenylene)s and poly(para-phenylenevinylene)s. 

Poly(para-phenylene)s PPPs and other polyarylenes represent structure-classes of conjugated polyhydrocarbons which are currently under intensive investigation [7]. This, in turn, is the result of important advances that have been made in the chemistry of aromatic compounds in recent years. 

Based on the results of the synthesis of oligo- and poly(para-phenylene)s PPPs (see Sects. 2.1-2.3) several investigators have studied the generation of other oligo- and polyarylenes. 

Knoevenagel-type condensation of 1,4-xylylene dinitriles and aromatic dialdehydes gives access to cyano-containing poly(para-phenylene-cyanovinylene)s (74). The insoluble parent systems (74a R, R = H) have been reported by... 

For the synthesis of the target structures, it is absolutely necessary to introduce solubilizing substituents in the positions peripheral to the benzoyl substituents. The primary coupling product, 117, a poly(2,5-dibenzoyl-l,4-phenyl-ene) derivative - a poly(para-phenylene) with two benzoyl substituents in each structural unit - is, as expected, very poorly soluble. Highly substituted monomers (2,5-dibromo-l,4-bis(3,4-dihexyloxy-benzoyl)benzene), containing four solubilizing alkoxy groups per monomer unit, allow the synthesis of polymeric materials with M of about 12,000 and M, of about 22,000 [139]. 

Schemed Examples for the convergently executed route A using poly([l.l.l]propellane) (a) and poly(para-phenylene) backbones (b, c)... 

Remarkably enough, dialkoxyterephthalic acids, both in 2D and 3D, form linear hydrogen bonded strands which are reminiscent of the rigid rods formed from alkyl substituted poly-para-phenylenes. 

G Grem, V Martin, F Meghdadi, C Paar, J Stampfl, J Sturm, S Tasch, and G Leising, Stable poly(para-phenylene)s and their application in organic light emitting devices, Synth. Met., 71 2193-2194, 1995. 

XH Yang, D Neher, U Scherf, SA Bagnich, and H Bassler, Polymer electrophorescent devices utilizing a ladder-type poly(para-phenylene) host, J. Appl. Phys., 93 4413 -419, 2003. 

D Hertel, S Setayesh, HG Nothofer, U Scherf, K Mullen, and H Bassler, Phosphorescence in conjugated poly(para-phenylene-derivatives), Adv. Mater., 13 65-70, 2001. 

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