Synthesis and optical properties of light-emitting π-conjugated polymers containing biphenyl and dithienosilole

Copolymers containing oligo(phenylene vinylene) (2.5), fluorene, and 4,4-dihexyldithienosilole (DTS) units were synthesized and characterized. The pi-conjugated monomers were joined with the palladium(0)-catalyzed Suzuki-Miyaura coupling reaction, thus forming either biphenyl- or phenyl-thiophene linkages. These polymers were photoluminescent, with the fluorescent quantum efficiency between 54 and 63% and with),lambda(max) for fluorescence at similar to 448 nm in tetrahydrofuran. The presence of 5% DTS in the copolymers had little influence on the optical absorption and emission wavelengths. Double-layer light-emitting-diode devices using these polymers as emissive layers had low turn-on voltages (3.5-4 V) and moderate external quantum efficiencies (0.14-0.30%). The results show that DTS plays a positive role in improving the charge-injection characteristics of poly(phenylene vinylene) materials. (c) 2007 Wiley Periodicals, Inc.