Alkyl-substituted PPVs

A general pieture of the photo-oxidation process in conducting polymers is presented in Fig. 15.2. Singlet oxygen reacts with the polymer and forms exciton traps. The result of the photo-oxidation process is that the polymer backbone is cut and exciton traps are formed on the chains. Photo-oxidation of alkyl-substituted PPVs has been studied extensively,and one possible reaction route is shown in Fig. 15.3. 

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-subslilutcd PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and fo/.v-boronic acid 30. Its absorption (2ni ix=385 nm) and emission (2max=475 nm) maxima were strongly... 

Two types of methathesis polymerization have been used to make PAVs. Thorn-Csanyi and coworkers have used transition-metal-mediated metathesis of divinyl-benzenes to make alkyl- and alkoxy-substituted PPVs, but the products are primarily oligomers [53,54]. 

The most commonly used polymeric electron donors are PPV and poly(alkyl thiophene)s. Polymeric electron acceptors are cyano substituted PPV and poly(p-pyridyl vinylene). There are also low-molecular-weight electron acceptors, which include fiillerenes and perylene derivatives, such as tetrabenzyl perylene-3,4,9,10-tetracarboxylate. ... 

Suzuki Coupling. PPV can also be synthesized by Pd-catalyzed coupling of alkyl-substituted aryldiboron acids with dibromo aromatic compounds (Fig. 67). Several derivatives have been synthesized in this way, among which poly(trisphenylene vinylene) [272, 705,878-880]. 

Glich polymerization is a dehydrohalogenation reaction which has been widely adopted to synthesize alkyl/alkoxy substituted PPV derivatives [37]. The reaction is a two-step process and is reported to proceed through the formation of quin-odimethane intermediate which is generated by radical/living chain anionic polymerization, Fig. 4. 

Horhold et al. and Lenz et al. [94,95]. The polycondensation provides the cyano-PPVs as insoluble, intractable powders. Holmes et al. [96], and later on Rikken et al. [97], described a new family of soluble, well-characterized 2,5-dialkyl- and 2,5-dialkoxy-substituted poly(pflrfl-phenylene-cyanovinylene)s (74b) synthesized by Knoevenagel condensation-polymerization of the corresponding alkyl-or alkoxy-substituted aromatic monomers. Careful control of the reaction conditions (tetra-n-butyl ammonium hydroxide as base) is required to avoid Michael-type addition. 

FIGURE 1.2. Molecular structure of widely used it-conjugated and other polymers (a) poly(para-phenylene vinylene) (PPV) (b) a (solid line along backbone) and it ( clouds above and below the a line) electron probability densities in PPV (c) poly(2-methoxy-5-(2 -ethyl)-hexoxy-l,4-phenylene vinylene) (MEH-PPV) (d) polyaniline (PANI) (d.l) leucoemeraldine base (LEB), (d.2) emeraldine base (EB), (d.3) pernigraniline base (PNB) (e) poly(3,4-ethylene dioxy-2,4-thiophene)-polystyrene sulfonate (PEDOT-PSS) (f) poly(IV-vinyl carbazole) (PVK) (g) poly(methyl methacrylate) (PMMA) (h) methyl-bridged ladder-type poly(jf-phenylene) (m-LPPP) (i) poly(3-alkyl thiophenes) (P3ATs) (j) polyfluorenes (PFOs) (k) diphenyl-substituted frares -polyacetylenes (f-(CH)x) or poly (diphenyl acetylene) (PDPA). 

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