Polymeric alkoxy PBD [2-(4-biphenylyl)-5-phenyl-1,3,4- oxadiazole] for light-emitting diodes

The syntheses are reported of the title polymeric alkoxyPBD derivative 5 and the dipyridyl analogue 12 using Suzuki coupling reactions of 1.4-dialkoxybenzene-2.5-diboronic acid with 2.5-bis(4-bromophenyl)-1,3,5-oxadiazole. and its dipyridyl analogue, respectively. Thermal gravimetric analysis shows that polymers 5 and 12 are stable up to 370 degreesC and 334 degreesC, respectively. Films of polymer 5 spun from chloroform solution show an absorption at lambda (max) = 367 nm, and a weaker band at 312 nm, and strong blue photoluminescence at lambda (max) = 444 nm. The photoluminescence quantum yield (PLQY) was found to be 27 +/- 3 %. For polymer 12. the absorption spectra reveal bands of equal intensity at lambda (max) = 374 and 312 nm, with PL at lambda (max) = 475 nm. Device studies using polymer 12 were hampered by its instability under illumination and/or electrical excitation. Polymer 5 is stable under these conditions acid acts as an efficient electron-transporting/hole-blocking layer. For devices of configuration ITO/PEDOT/ MEH-PPV/polymer 5/Al an external quantum efficiency of 0.26% and brightness of 500 cd/m(2) was readily achieved: orange emission was observed, identical to the MEH-PPV electroluminescence.