Alkoxy substituted PPV

Substituted soluble PPV derivatives may also be synthesized by step-growth polymerization methods. Arylene-fc/.v-phosphylidenes may be condensed with ler-ephthaldehydes in a Wittig fashion to yield alternating PPV copolymers [52]. An alkoxy-substituted PPV derivative 28 (Scheme 1-8) prepared in this fashion emits in the orange (2nmx=585 nm) region of the spectrum [52]. 

The sulfonium precursor route may also be applied to alkoxy-substituted PPVs, but a dehydrohalogenation-condensation polymerization route, pioneered by Gilch, is favored 37]. The polymerization again proceeds via a quinomethide intermediate, but die syndicsis of the conjugated polymer requires only two steps and proceeds often in improved yields. The synthesis of the much-studied poly 2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene vinylene], MEH-PPV 15 is outlined in Scheme 1-5 33, 35]. The solubility of MEH-PPV is believed to be enhanced by the branched nature of its side-chain. 

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]. 

Different alkoxy-substituted poly(p-phenylenevinylene)s (PPVs) have been examined to relate performance to the substitution on the phenyl ring (symmetric 40b, 40e or asymmetric 40a, 40c, 40d) and nature of side chain, either linear or branched.[233-235] The PPV polymers were soluble in common organic solvents and OTFTs were fabricated by spin-casting a 0.3 wt % solntion of PPV in chlorobenzene. Unsymmetrical alkoxy-substituted PPVs gave mobilities on the order of 10 cm V s, compared to 0.01 cm V s for symmetrically snbstimted polymers. 

Carbonnier, B., T. Pakula, and D.A.M. Egbe. 2005. Self-organization of comb-like macromolecules comprised of four-fold alkoxy substituted (PPV-PPE) rigid backbone repeat units Role of length variation of side chains attached on phenylene ring surrounded by vinylene moieties. J Mat Chem 15 880. 

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. 

The side-chain functionalization of PPV derivatives has recently progressed to include polymers which are soluble in the final conjugated form. Three new alkoxy substituted PPV s have been synthesized, all of which are soluble in the fully converted conjugated form (see Figure 1.2) [6]. Poly(dihexyloxy phenylenevinylene) (DHO-PPV) is soluble at temperatures above 80° C. Surprisingly, the octyloxy derivative (DOO-PPV) was found to be less soluble in most non- polar organic solvents (probably because of side... 

Substituted PPVs have been prepared using similar techniques. The earliest reports described methyl substituents (104,105), and more recentiy alkoxy substituents on the aromatic ring have been incorporated into the polymer stmctures (107—109). The advantage of long-chain alkoxy (butoxy or hexyloxy) substituents is that not only is the precursor polyelectrolyte soluble, but after conversion the substituted PPV is also soluble (110—112). 

Heteroaromatic ring stmctures can also be incorporated into poly(arylene vinylene) stmctures using the same precursor polymer method shown for PPV. Poly(thienylene vinylene) (13) (113—118) and poly(furylene vinylene) (14) (119,120) have been prepared in this manner. In addition, alkoxy-substituted poly(thienylene vinylenes) (15) (119,121) have been synthesized. Various copolymers containing phenjiene, thienylene, and furylene moieties have also been studied (120,122,123). 

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... 

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. 

The diphenylamino-substituted PPV107, with solubilizing alkoxy groups, was synthesized by Shi and Zheng [150] via Wittig-Horner reaction (Chart 2.23). Its PL (555 nm) is very similar to that of diamino-PPV 64 and dialkoxy-PPV 14 homopolymers. The PLQY is rather high in solution (80%), but it drops to only 8% in films. Consequently, only a moderate EL efficiency of 0.6cd/A was obtained with this material (device ITO/PEDOT/107/Mg/Al) [150]. Almost simultaneously, Kido and coworkers [151] reported a similar diphenylamino-substituted PPV copolymer 108, which affords very efficient PLEDs. The device ITO/PEDOT/108/Ca/Al... 

Cyano-substituted PPVs have low electrical conductivity due to the electron withdrawing ability of cyano group, however, they have become important materials for the fabrication of LEDs. While LED devices constructed from unsub-stituted-PPV exhibit efficiencies of less than 1%, similar LED devices fabricated with cyano-substituted PPVs have displayed efficiencies of over 4%. To further enhance device performance, proccessible polymers containing cyano functionalities were synthesized utilizing monomers possessing solubilizing alkoxy chains for ease of device construction. 

PPV derivatives can be prepared by water-soluble precursor route [14-16] involving sulfonium polyelectrolyte or organic-soluble precursor route [3,17,18] involving alkoxy substituted non-ionic form, respectively. The representative synthetic pathways for PPV derivatives are shown in Scheme 1. 

Substituted PPVs are of particular interest in relation to electronic applications (Section V) both because processibility can be improved and because electronic structure can be fine tuned by suitable substitution. However, no homogeneous series such as the P3ATs exists for PPV. Up to now most substitution of PPV has been by alkoxy groups (i.e., OC H2 +1), and in many cases only low-molecular-weight materials are obtained, so less is known than for the P3ATs. There are few long side groups, with the notable exception of MEH-PPV. 

Color is another important factor for control in polymer LEDs. The emission spectrum of PPV, shown in Fig. 5.5, corresponds to green emission. As mentioned in Section 5.3, alkoxy substitution can be used to shift the emission toward the... 

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