Oxadiazole groups

The recently synthesized PPV 68, in which the oxadiazole group is separated from the PPV backbone by an oxygen atom, is a very soluble material with optical band gap of 2.36 eV and yellowish-orange emission color (chromaticity coordinates by the Commission Internationale de l Eclairage, CIE a 0.50, y = 0.47 591 nm) [124]. An extremely high-... 

Corresponding electron-transport materials have been made by replacing the amino substituents in the first shell by oxadiazole groups (29) [70, 61] or phenyl-quinoxalines (30) [60]. As in the case of the amines, dendrimer-shaped structures are obtained by repeating the substitution pattern in a second shell (31) [76], The Tg was increased from 142°C in 29 to 222° C in 31. 

Anthrimides and Other Linked Anthraquinones. Among the anthrimides (dia-nthraquinonyl-amines), only the a,(3 derivatives have achieved limited importance as vat dyes. Coupling two anthraquinone molecules via functional derivatives of the 2-aldehyde (or 2-carboxy) group offers another type of building block for vat dyes. Such compounds, e.g., 1-aminoanthraquinones, are linked in the 2-position via an azine or oxadiazole group, and all have good fastness. 

In blends of PVK with PBD and in random copolymers with carbaz-ole and oxadiazole groups attached as side chains, the active groups have different mobility, or are subjected to different topological constraints, respectively. In the blends, exciplexes emerge, and in the copolymers, electroplexes are effective. Both types of complexes shift the EL spectra to red in comparison to pure PVK homopolymer. The red-shift is significantly greater for the electroplex. 

Copolymers having the carbazole group and the oxadiazole group directly in the backbone, i.e., poly[3,6-A-Ethylcarbazole-l,3,4-oxadiaz-ole-2,5-diyl], can be prepared from A-ethylcarbazole-3,6-dicarboxylic acid and hydrazine hydrochloride.The reaction runs at 140°C with PPA. The synthesis is shown in Figure 10.4. 

The oxadiazole group is already present in 2,2 -(oxydi-4,l-phenyl-ene)bis[5-(4-fluorophenyl)-l,3,4-oxadiazole], c.f. Figure 10.1. The compound can he condensed with various naphthalenedioles, such as 1,5-na-phthalenediol to result in PODA types. AH polymers are amorphous materials and some of them are soluble in aprotic solvents. Alkylated 2,7-dibromo-9H-fluorene compounds, with pendent carhazole and oxadiazole units can be condensed with nickel catalysts. ... 

Several oxadiazole derivatives, not necessarily polymers, find use in light-emitting devices." This is justified, because the oxadiazole group is one of the best electron transport structures. A conunon material is 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-l,3,4-oxadiazole (PBD), which acts as electron transporting material. PBD is not a polymer, but rather a low-molecular-weight compound. 

Oxadiazole groups provide for efficient electron transport. Insertion of these groups into p-type polymers facilitates bipolar carrier transport. 

The syntheses and properties of different polymers containing high electron affinity CF3 and oxadiazole groups have been reviewed. It has been shown that when CF3 groups are incorporated into conjugated polymers, such as poly(phenylene vinylene) derivatives, the polymers with CF3 substituents show better electron accepting properties. This makes it possible to use stable aluminum in place of air sensitive calcium as metal cathode in polymer LEDs. 

Modified polymers of PPV with pendant carbazol groups and oxadiazole groups have been prepared by direct polymerization of the respective o(,a-dibromo-p-xylene monomers [103]. 

PBD may exhibit short operating lifetimes due to recrystallization or aggregate formation. This leads to phase separation and formation of charge carrier traps that inhibit the desired emission. Therefore, it has been proposed to bond the PBD electron transporting structure to a polymer chain, which results in amorphous materials. For example, poly(methyl methacrylatejs with oxadiazole side chains have been reported [71]. The oxadiazole group may be part of the polymeric backbone, together with carbazole moieties or pheny-lene vinylene moieties [25,26]. 

One of the best electron transport structures is the oxadiazole group, as noted above. The covalent attachment of the PBD moiety to an emitting polymer (Fig. 47.4(b)), was a natural development in LED technology, avoiding the... 

Gruner, J., Friend, R. H., Huber, J., and Scherf, U., A blue-luminescent ladder-type poly(para-phenylene) copolymer containing oxadiazole groups, Chem. Phys. Lett., 251, 204-210 (1996). 

For selected examples, see (a) J. C. Legeay, J. J. V. Eynde, L. Toupet, J. P. Bazureau, Arkivoc 2007, (iii), 13-28. A three-component condensation protocol based on ionic liquid phase bound acetoacetate for the synthesis of BigineUi 3,4-dihydro-pyrimidine-2(17/)-ones. (b) J. C. Legeay, J. J. V. Eyndeb, J. P. Bazureau, Tetrahedron Lett. 2007, 48, 1063-1068. A new approach to N-3 functionalized 3,4-dihydropyrimidine-2(l//)-ones with 1,2,4-oxadiazole group as amide isostere via ionic Uquid-phase technology. 

Legeay JC, Vanden Eynde JJ, Bazureau JP (2007) A New Approach to N-3 Functionalized 3,4-Dihydropyrimidine-2-(l H)-ones with 1,2,4-Oxadiazole Group as Amide Isostere via Ionic Liquid Technology. Tetrahedron Lett 48 1063-1068... 

The oxadiazole 1 is a hole transport material since the electron withdrawing effect of the oxadiazole group with three electronegative heteroatoms is overcompensated hy two electron donating amino groups. 

Oligo and polysiloxanes with pendant oxadiazole groups... 

The next step was the synthesis of liquid crystalline polysiloxanes with oxadiazole groups in the mesogenic unit. The polymers were prepared by a polymeranalogous reaction of the monomers 10 and 11 with poly(hydrogenmethylsiloxane) 15. 

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