Thiophene-based conjugated polymers for light-emitting diodes: Effect of aryl groups on photoluminescence efficiency and redox behavior

An efficient and convenient approach to a series of soluble conjugated poly mers, poly[(4-n-hexylthiophene-2,5-diyl)(arylene)(4-n-hexylthiophene-2,5-di yl)]s, has been developed. The reductive coupling polymerization reaction u sing Ni(0) catalyst provides the desired polymers with well-defined and hig h regioregularity of 5 and 5' linkage between two adjacent thiophene rings. Their structures and purification are verified by FT-IR, H-1 and C-13 NMR, and elemental analysis. It is demonstrated that the inserted aromatic grou ps not only change the optical spectra and the electronic structures of the polymers, which are demonstrated respectively by the optical spectra and e lectrochemical measurements of the polymers, but also remarkably affect the absolute photoluminescence (PL) quantum yield of the polymers in solid fil ms. Green light-emitting PLEDs devices with single and multiple layers usin g poly[(4-n-hexylthiophene-2,5-diyl)(9,9-di-n-hexylfluoren-2,7-ylene)(4-n-h exylthiophene-2,5-diyl)] as the emissive layer are fabricated from the poly mer with the highest PL quantum yield and best electroluminescent (EL) perf ormance.