Synthesis and optoelectronic properties of new fluorene-2,5-diaryl-1,3,4-oxadiazole hybrid materials
Novel fluorene and spirobifluorene-2,5-diaryl-l,3,4-oxadiazole hybrids 165 and 171, respectively, have been synthesised by Suzuki cross-coupling methodology. Pyridine analogues of 165 and 171,184 and 185, respectively, were also synthesised. Further extension of the π-electron framework was achieved via Wittig reaction to afford compound 177. Single layer organic light emitting devices (OLED)s using blends of MEH-PPV as the emissive material with electron transport (ET) materials 165, 171, 177， 184 and 185 have been fabricated. For all the devices studied electroluminescence (EL) originated exclusively from the MEH-PPV with external quantum efficiencies (EQE)s greatly enhanced (>two orders of magnitude) compared to pure MEH-PPV devices. The incorporation of pyridine in compounds 184 and 185 considerably enhanced the electron affinity of the systems compared to compounds 165 and 171. For a device incorporating PEDOT:PSS in the configuration ITO/PEDOT:PSS/MEH-PPV-185 (30 ： 70% by weight)/Ca/Al an EQE of ca. 0.6% and a luminance efficiency of 1.2 cd A—i at 10.5 V was achieved.