PPV derivatives

Ordered dialkoxy PPV derivative has been prepared by Yoshino et al. [491. oly(2 -nonoyloxy-1,4-phenylene vinylene) 27a forms a nematic liquid-crystalline phase upon melting. The material retains its order upon cooling to room temperature, and its band gap (2.08 eV) is measurably smaller than in an unoricnted sample. Oriented electroluminescence may be achieved by rubbing a thin fdin of the material to induce molecular orientation [50],... 

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]. 

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... 

EL experiments showed that the yellow-emitting LEDs prepared from LPPP 12 exhibit quite remarkable characteristics (single layer construction ITO/LPPP 12/Ca quantum efficiency ca. 1.0%, applied voltage 4-6 V 135]). These figures are in the range of the best values described hitherto for polymeric emitters in a single layer arrangement, for example, poly(pcira-phenylenevinylene) PPV and PPV derivatives. 

Our results also shed light on the long-lived PA3 band detected in transient PM measurements of P3BT (see Fig. 7-19) and can explain changes in the PA spectra observed in several ps transient measurements of films of PPV derivatives at energies around 1.8 eV [9, 25, 60J. In good PPV films the transient PA spectrum shows a PA band of excitons at 1.5 eV whose dynamics match those of the PL and stimulated emission (SE) [9J. However, in measurements of oxidized [25] or C60-doped films 60, there appears a new PA band at about 1.8 eV whose dynamics are not correlated with those of the PL and SE. Based on our A-PADMR results here, we attribute the new PA band at 1.8 eV to polaron pair excitations. These may be created via exciton dissociation at extrinsic defects such as carbo-... 

Poly(l,4-phenylene vinylcne) and its Derivatives 2 The Basic Polymer LED Device Architecture 4 Substituted Poly(phcnylene vinylcne)s 6 Poly(anthrylenevinylcne)s 10 Step-Growth Routes to PPV Derivatives 10 PPV Copolymers 11... 

Electron-Deficient Polymers - Luminescent Transport Layers 16 Other Electron-Deficient PPV Derivatives 19 Electron-Deficient Aromatic Systems 19 Full Color Displays - The Search for Blue Emitters 21 Isolated Chromophores - Towards Blue Emission 21 Comb Polymers with Chromophores on the Side-Chain 22 Chiral PPV - Polarized Emission 23 Poly(thienylene vinylene)s —... 

Scheme 1-8. Examples of soluble, dialkoxy-substituted PPV derivatives.

Scheme 1-12. Synthesis of PPV derivatives incorporating triarylamines a) KOtBu, toluene.

Scheme 1-17. High-electron-affinity PPV derivatives with electron-withdrawing groups on the aromatic ring.

Substitution at the vinylcnc carbon position of PPV derivatives reduce their tendency to oxidation. Examples (see Table 13-1) are CN-PPV 12 and DPOP-PPV... 

The general process involves polymerization of l,4-bis(dialkylsulfoniome-thyl)benzene dihalides (61) by addition of base. The immediately formed polyelectrolyte (62) is then converted thermally to the final PPV derivative (63). The process was first developed for the synthesis of unsubstituted PPV 60. The mechanism of the Wessling process is still not fully clear. First, Horhold et al. 

The final elimination step in which the conjugated PPV derivative (63) is generated from the sulfonium polyelectrolyte precursor polymer (62) was reported by Wessling and Zimmerman to be heating in vacuo to 200 - 300°C. The target PPV derivative is formed with elimination of dialkyl sulfide and hydrogen halide the process can be easily monitored by UV/Vis spectroscopy. PPVs... 

Since the products often precipitate during the polymerization, a modification was reported by Swatos et al. [82] involving the use of only about one equivalent of f-BuOK. This method, the so-called chlorine precursor route , first gives a soluble non-conjugated precursor (66) which is then converted thermally in the film or in a high boiling solvent, e.g. cyclohexanone. In the latter case, homogeneous solutions of (soluble) PPV derivatives 63 can be obtained. 

The generation of PPV and corresponding derivatives via the dihalide approach is possible not only in solution reaction, but also - via the gas phase -in a so-called chemical vapor deposition (CVD) process. In this process, the vapor of a dichlorinated para-xylene (a,a or a,a) is pyrolyzed at moderately low pressures (0,1-0,2 torr) to form a chlorinated para-xylylene intermediate, which then condenses and polymerizes on a suitable, cooled substrate. The coating of the chlorinated precursor polymer can be heated to eliminate HCl, to form PPV 60 (or a PPV derivative) [88]... 

The polymerization methods to PPV and PPV derivatives described in the previous section involve 1,6-polymerization of an immediately formed 1,4-xylyl-ene derivative. Aside frome this polymerization approach, a broad spectrum of polycondensation procedures (step-growth methods) to PPV and PPV derivatives has been developed. The methods can be classified as follows ... 

A second example of step-growth polycondensations with formation of the ole-finic double-bond are Wittig- and Wittig-Horner-type condensations. The Wittig-type polycondensations involve AA/BB-type reactions of aromatic bisal-dehydes with bisphosphonium ylides [99,100] with formation of PPV derivatives (75) and lead to products of only moderate molecular weight (DP 10-20). 

The Wittig-Horner procedure, starting from bisphosphonate or aromatic bisphosphine oxide monomers, allows for AA/BB-coupling of the PO-activated bismethylene monomers, not only with aromatic dialdehydes but also with aromatic diketones to the corresponding PPV derivatives (76), and for the selfcondensation of AB-type aromatic starting compounds containing both alde-hyde/keto and PO-activated methylene functions [101]. 

The synthesis of soluble PPV derivatives (82), via McMurry-type coupling of solubilized aromatic dialdehydes in the presence of low-valent titanium reagents, was described by Schliiter et al. [105]. The products are characterized... 

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). 

The synthesis of a PPV derivative, 94, with donor (di-n-hexylamino) and acceptor (nitro) substituents attached regioselectively to the PPV backbone, was published by Yu et al. following the Heck-type cross coupling approach [118] starting from an AB-type monomer (95). The red-orange polymer (94), which is soluble in THE, chloroform and 1,2-dichloroethane, displays a number-average molecular weight M of about 12,000. 

A general and most widely used method for the synthesis of PPV derivatives was introduced by Gilch and Wheelwright [33]. This method avoids high-temperature conditions and occurs through base-promoted 1,6-elimination of 1,4-/Ys(chloro/bromomethyl)bcnzcncs 7 (Scheme 2.4). For device applications, the as-synthesized PPV materials need to be soluble... 

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