Phenylene representative examples

Polyfarylene vinylene)s form an important class of conducting polymers. Two representative examples of this class of materials will be discussed in some detail here. There are poly(l,4-phenylene vinylcne) (PPV) 1, poly(l,4-thienylene viny-lenc) (PTV) 2 and their derivatives. The polymers are conceptually similar PTV may be considered as a heterocyclic analog of PPV, but has a considerably lowci band gap and exhibits higher conductivities in both its doped and undoped stales. The semiconducting properties of PPV have been shown to be useful in the manufacture of electroluminescent devices, whereas the potential utility of PTV has yet to be fully exploited. This account will provide a review of synthetic approaches to arylene vinylene derivatives and will give details an how the structure of the materials relate to their performance in real devices. 

Alternatively, a spacer can be inserted between the heterocyclic rings to further modify the properties of the polymer. Although various spacers have been used, aromatic rings are probably the most frequently employed. In this case, 2,2 -(p-phenylene)bis[4,4 -dimethyl-5(4//)-oxazolone] 330 is the most common monomer (Fig. 7.34). Again, representative examples are described in selected references... 

Other components of the design [138—142] include the choice of the crown size or even the use of open-chain metalloclefts, not necessarily polyether armed. The issue of special importance for extraction and transport applications is the selection of substituents ensuring a necessary lipo-philicity-solubility balance. For example, use of a cyclohexano moiety as shown above, instead of the more common o-phenylene bridge between nitrogens, enhances solubility in the membrane phase. The modification of the polyether chain with binaphthyl or calixarene substituents provides high membrane transport rates due to increased ionophore lipophilicity [138,142]. Some representative examples (initial fluxes, in 10 mol cm h , through o-nitrophenyloctyl ether-impregnated Accurel membrane 1 M source urea [138]) are as follows. 

At first sight the excited state lattice distortions of poly(para-phenylene) represented in Fig. 11.15 do not resemble those of a linear polyene. We therefore might enquire whether the geometrical defects (for example, solitons, polarons, etc.) and their associated mid-gap electronic states also exist in an analogous maimer in poly(para-phenylene). To show that bond defects do exist in an analogous manner to linear polyenes we again consider the summed bond distortions, defined by eqns (11.18) - (11.20). 

In 1993, Scherf and Chmil described the first synthesis of a ladder-type poly(pflra-phenylene-czs-vinylene) (116) [138]. On the one hand, ladder polymer 116 represents, a planar poly(phenylene) containing additional vinylene bridges on the other hand, it is a poly(phenylenevinylene) with aryl-aryl linkages in the polymeric main chain. The target macromolecules, as fully aromatic ladder polymers, are composed of all-carbon six-membered rings in the double-stranded main chain (an example of angularly annelated poly(acene)s). 

Copolymer 459, prepared by Stille coupling of dibromophenylene with 2,5-Mv(tributyl-stannyl)thiophene, represents another example of a phenylene-u/t-thiophene backbone, where the substituted phenylene unit forms an oligophenylene vinylene fragment that is not in the main conjugation chain [561]. A PLED fabricated with this polymer (ITO/459/A1) emitted green light (520 nm) with a turn-on voltage of ca. 9.5 V, but no other data on luminance or efficiency of the device were reported (Chart 2.111). 

A common structural feature of compounds 81-89 is their distorted tetrahedral coordination geometry at zinc. A trend that can be observed in Table 5 is that with increasing Zn—O distances, the C—Zn—C angle also increases and consequently the O—Zn—O angle decreases. From a structural point of view 83 has interesting structural features. In this complex two 1,2-phenylene dianionic units are C, C-bridge bonded between two zinc atoms (Figure 45) and it represents one of the few examples of polymetallated compounds for which the structure has been established by an X-ray crystal structure determination . 

The ability to polymerize readily via selective oxidation utilizing the abundant and cheap oxidant 02 often represents a desirable low-cost method for upgrading the value of a raw material. The most successful example is the oxidative polymerization of 2,6-dimethylphenol to yield poly(2,6-dimethyl-l,4-phenylene ether) with copper-amine catalysts under an 02 atmosphere at room temperature. Thiophenol also has a labile hydrogen but is rapidly oxidized to yield thermodynamically stable diphenyl disulfide. This formation is based on the more facilitated formation of S—S bond through radical coupling [82] in comparison with the formation of C—S—C bond through the coupling with the other molecules in the para position (Eq. 9). 

The chiral dendrimer (Figure 3.6 17 ) in its racemic form represents an example of the class, its name is rac-14-Cascade benzyloxyethane[3-2,2,2,2] [(5-(2-oxapropyl)-l,3-phe-nylene) (2-oxaethyl)benzene] [(5-(2-oxapropyl)-l,3-phenylene) (5-(2-oxaethyl)-l,3-phe-nylene) (2-oxaethyl)benzenej [(5-(2-oxapropyl)-l,3-phenylene) (5-(2-oxaethyl)-l,3-phe-nylene)2 (2-oxaethyl)benzene]. 

The synthetic sequence to methylene-bridged poly(phenylene)s 71 represents the first successful employment of the stepwise process to ladder-type macromolecules involving backbone formation and subsequent polymer-analogous cyclization. As shown, however, such a procedure needs carefully tailored monomers and reaction conditions in order to obtain structurally defined materials. The following examples demonstrate that the synthesis of structurally defined double-stranded poly(phenylene)s 71 (LPPP) via a non-concerted process is not just a single achievement, but a versatile new synthetic route to ladder polymers. By replacing the dialkyl-phenylenediboronic acid monomer 68 by an iV-protected diamino-phenylenediboronic acid 83, the open-chain intermediates 84 formed after the initial aryl-aryl cross-coupling can te cyclized to an almost planar ladder-type polymer of structure 85, as shown recently by Tour and coworkers [107]. 

The polycyclic version of the star graph is represented by Diercks and Voll-hardt s triangular [4]phenylene (87), or starphenylene [121]. Some earlier examples are trifoliaphane (88) by Hopf and Psiorz [122], its meta-linked isomer by Vogtle and Kissener [123], and decacyclene (89) for which the crystal structure was only recently reported [124]. 

---