Side-chain aromatic oxadiazole

An alternative approach utilizes polymeric analogs of PBD. The oxadiazole unit may be in the polymer main chain or attached as a side chain. A reasonable device performance has been demonstrated in poly(aromatic oxadia/ole)s [71—74. ... 

H. Meng, W. Yu, and W. Huang, Facile synthetic route to a novel electroluminescent polymer — poly(p-phenylene vinylene) containing a fully conjugated aromatic oxadiazole side chain, Macromolecules, 32 8841-8847, 1999. 

Thiadiazoles like oxadiazoles are 7r-electron deficient systems. When fused to azines, electrophilic substitution on carbon is only to be expected in the presence of strongly electron-donating substituents. Thus the lactams (666) and (667) are activated for electrophilic substitution (74BCJ2813), whereas in the absence of an activating substituent the electrophile may attack an aromatic side-chain as in the case of (668) (70JOC1965). 

Interestingly, polymer 18 was found to emit blue-purple light. Aromatic oxadiazole compounds are known to show blue electroluminescence (40-42), Main chain oxadiazole polymers can also be made fluorescent by proper modification of the chemical structure. Pei and Yang (43,44) have reported a new oxadiazole polymer 25 with both a flexible linkage and solubilizing alkoxy side-chains (Scheme 7). An LED of structure ITO/polyaniline/polymer 25/Al has an external quantum efficiency close to 0.1 % and a tum-on voltage around 4.5 V. 

Soluble main chain oxadiazole polymers can be realised using solubilizing side groups such as tert-bu y and long flexible alkoxy or alkyl groups. Alternatively, flexible spacers can be incorporated between aromatic oxadiazole units, and finally a soluble precursor route may be employed. 

Although a wide variety of heterocycle/side-chain combinations can be used in the Boulton-Katritzky rearrangement, among these, the most commonly used heterocycle has been the 1,2,4-oxadiazole. This is due to the relative ease with which it is synthesized as well as the fact that it has a very low index of aromaticity. Its heightened chemical reactivity has made it an important target for medicinal and materials chemists and the subject of multiple reviews in the last several years. ... 

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