Organic-soluble PPV derivatives

S. Chung, J. Jin, C.H. Lee, and C.E. Lee, Improved-efficiency light-emitting diodes prepared from organic-soluble PPV derivatives with phenylanthracene and branched alkoxy pendants, Adv. Mater., 10 684-688, 1998. 

A PPV derivative which is twofold phenylsubstituted at the vinylene unit, poly(l,4-phenylene-l,2-diphenylvinylene DP-PPV), (71b) (see also the discussion of dehydrochlorination of unsymmetrically substituted para-xylylene dichlorides in Section 3.1) was first synthesized by Smets et al., using acid-catalyzed elimination of nitrogen from l,4-bis(diazobenzyl)benzene 83 [106]. The yellow products obtained are fully soluble in common organic solvents (toluene, chloroform, ethylene chloride, DMF, THF). 

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. 

These problems were eliminated by the use of modified PPV derivatives ", such as poly[2-methoxy-5-(2-ethylhexyloxy)-4-phenylene vinylene] (MEH-PPV) compound 2, see Table 6.1, which are soluble in organic solvents. The presence of lateral substituents in the polymers 3-6 shown in Table 6.1 induces a lower... 

Substituted PPVs are soluble in organic solvents, which is a very useful feature in the preparation of polymer LEDs. One of the first PPV soluble derivatives, prepared by the Santa Barbara group in California via the precursor route, was methoxy-ethylhexyloxy PPV (MEH-PPV), which emitted a red-orange color [107,108]. Subsequently another PPV derivative with the bulky cholestanoxy group was prepared, namely the poly [2,5-bis(3a-5b cholestanoxy)-1,4-pheny-lene vinylene] (BCHAPPV). A blue shift was observed in relation to MEH-PPV BCHA-PPV emitted in the yellow region [109,110]. 

Another effort to prepare a soluble main-chain conjugated polymer was made by Holmes, Bradley and co-workers (67-69J. The nitrile-substituted PPV derivative (cyano-PPV) was synthesized by the Wittig reaction and was soluble in common organic solvents. This polymer has high electron afflnity because of the electron-attracting nitrile group. 

Alkoxy Precursor Route. Sulfonium precursor polymers can be readily converted to methoxy-substituted polymers, which are soluble in organic solvents and which are much more stable than the sulfonium precursor. The alkoxy group can be removed by acid catalysis and/or heating to produce fully converted PPV derivatives [950, 968, 970]. 

A series of PPV derivatives containing a dimethyldodecylsilylphenyl unit as a pendant group was reported by the Jin group (Fig. 39) [172-174]. All polymers were completely soluble in common organic solvents, had high thermal stability (up to 400°C), and were used as emitting layer in OLEDs. Poly[2-(4-dimethyldodecylsilylphenyl)-l,4-phenylenevinylene] (/7-SiPhPPV), synthesized via... 

Reynold et al. [133] developed CN-PPV derivatives containing dioxythiophene moieties in the main chain which revealed narrow band gaps ranging between 1.5-1.8 eV and good solubilities in common organic solvents. Fig. 22. 

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... 

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