Para-phenylene

Ortho and para phenylene dithioureas (128) treated with a-halocarbonyl compounds afford NN -ortho- and para-phenylene-bis(2-amino-4-R-thiazole) (129) (Scheme 62) (653). 

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).

The PL spectrum and onset of the absorption spectrum of poly(2,5-dioctyloxy-para-phenylene vinylene) (DOO-PPV) are shown in Figure 7-8b. The PL spectrum exhibits several phonon replica at 1.8, 1.98, and 2.15 eV. The PL spectrum is not corrected for the system spectral response or self-absorption. These corrections would affect the relative intensities of the peaks, but not their positions. The highest energy peak is taken as the zero-phonon (0-0) transition and the two lower peaks correspond to one- and two-phonon transitions (1-0 and 2-0, respectively). The 2-0 transition is significantly broader than the 0-0 transition. This could be explained by the existence of several unresolved phonon modes which couple to electronic transitions. In this section we concentrate on films and dilute solutions of DOO-PPV, though similar measurements have been carried out on MEH-PPV [23]. Fresh DOO-PPV thin films were cast from chloroform solutions of 5% molar concentration onto quartz substrates the films were kept under constant vacuum. 

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)... 

The diaminobenzenes are made from benzene by a combination chlorination-nitration route although para-phenylene diamine is also made directly from aniline. orr/to-Phenylene diamine is widely used for the preparation of biologically active compounds such as fungicides and veterinarian medicines. The mera-diamine is used in fire-retardant textile fibers ( Nomex ) while the / ara-diamine finds use in high-strength textile fibers used for bullet-proof vests, sails, army helmets, and other types of fiber-reinforced plastics ( Kevlar ). 

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. 

The first series of soluble oligo(para-phenylene)s OPVs (20) were generated by Kern and Wirth 1331 and shortly thereafter by Heitz and Ulrich [34]. They introduced alkyl substituents (methyls) in each repeat unit and synthesized oligomers (20) up to the hexamer. Various synthetic methods, like copper-catalyzed Ullmann coupling, copper-catalyzed condensation of lithium aryls, and twofold additon of organometallic species to cyclohexan-l,4-dione, have been investigated. 

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)... 

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