Synthesis and luminescence properties of poly(p-phenylenevinylene) derivatives carrying directly attached carbazole pendants

New organic soluble poly(p-phenylenevinylene) (PPV) derivatives (polymers 1 and 2) that carry hole-transporting carbazole pendants were synthesized and their photo- and electro-luminescence properties were studied. The first one is poly[2-(carbazol-9-yl)-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (polymer 1) which has both carbazole and 2-ethylhexyloxy pendant groups. The other one is poly[2-(carbazol-9-yl)-1,4-phenylenevinylene] (polymer 2) which has only the carbazole pendant group attached to the main chain phenylene ring. We fabricated single-layer EL devices using indium-tin oxide (ITO) coated glass anodes and aluminium cathodes and investigated their electrical characteristics. The EL device of polymer 2 emits green light (λ_max=490 nm) with the EL efficiency being lower than that of PPV. But the EL device of polymer 1 emits bright yellow-green light (λ_max=530 nm) and its external quantum efficiency was 550 times the efficiency of polymer 2 and 60 times that of a PPV EL device with the same configuration. Especially, the EL device with the configuration ITO coated glass/poly(3,4-ethylenedioxy-2,4-thienylene)/polymer 1/Ca/A1 showed a low turn-on electric field of 0.31 MV cm^-1 and a high photometric efficiency of 4.4 cd A^-1 with maximum luminance being 30 390 cd m^-2 at an electric field of 1.50 MV cm^-1. Polymer 1 appears to perform better in EL than MEH-PPV.