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 polymers, poly[(4-n-hexylthiophene-2,5-diyl)(arylene)(4-n-hexylthiophene-2,5-diyl)]s, has been developed. The reductive coupling polymerization reaction using Ni(0) catalyst provides the desired polymers with well-defined and high 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 groups not only change the optical spectra and the electronic structures of the polymers, which are demonstrated respectively by the optical spectra and electrochemical measurements of the polymers, but also remarkably affect the absolute photoluminescence (PL) quantum yield of the polymers in solid films. Green light-emitting PLEDs devices with single and multiple layers using poly[(4-n-hexylthiophene-2,5-diyl)(9,9-di-n-hexylfluoren-2,7-ylene)(4-n-hexylthiophene-2,5-diyl)] as the emissive layer are fabricated from the polymer with the highest PL quantum yield and best electroluminescent (EL) performance.