Highly Efficient Light-Emitting Polymers Composed of Both Hole and Electron Affinity Units in the Conjugated Main Chain

Two new fully conjugated alternating copolymers containing both carbazole and oxadiazole units were prepared through the Wittig condensation polymerization (carbazole units were linked with oxadiazole units by meta and para). The polymers with the para linkage (PPOX−CAR) and the meta linkage (PMOX−CAR) in the main chain were soluble in common organic solvents and thermally stable on heating (the weight loss was less than 5% on heating to about 400 °C under nitrogen atmosphere). The maximum photoluminescence and the electroluminescence wavelengths of PPOX−CAR and PMOX−CAR were varied from 495 nm in the greenish-blue emission region to 450 nm in the blue emission region depending on the kink structure. The turn-on voltages of PPOX-CAR and PMOX-CAR were 7.5 and 10.5 V, respectively, when the single-layer light-emitting diodes of Al/PPOX-CAR or PMOX-CAR/ITO glass were fabricated. The maximum brightness of the Al/PPOX-CAR/ITO single-layer device was 500 cd/m2 at 20 V.