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 °C and 334 °C, respectively. Films of polymer 5 spun from chloroform solution show an absorption at λmax = 367 nm, and a weaker band at 312 nm, and strong blue photoluminescence at λmax = 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 λmax = 374 and 312 nm, with PL at λmax = 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 and 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 800 cd/m2 was readily achieved: orange emission was observed, identical to the MEH-PPV electroluminescence.
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Wang et al. (2001) studied this question.