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Optical and electronic properties of 3,4-dialkylthiophene-based p-/n-alternating copolymers



Four novel highly soluble p-/n-poly[(2,5-divinyl-3,4-dialkylthiophene)-alt-2,6-pyridine] (PA2TV-Py) and poly[(2,5-divinyl-3,4-dialkylthiophene)-alt-(2,5-diphenyl-1,3,4-oxadiazole)] (PA2TV-OXD) are prepared by Heck coupling approach to compare their photoelectric properties. Characterizations of the copolymers include FT-IR, 1H-NMR, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), UV–vis spectroscopy, photoluminescence (PL), and electroluminescence (EL). Four alt-copolymers exhibit excellent solubility in common organic solvents (e.g., CHCl3, THF) and good thermal stabilities, losing less than 5% on heating to ∼ 250°C. The optical properties depict that the band-gap energy of PA2TV-Py and PA2TV-OXD is similarly, ranging from 2.68 to 2.80 eV in solid film and 2.90–2.97 eV in CHCl3 solution. PA2TV-Pys can emit bright turquoise light with quantum efficiencies (QE) of 30.6 and 53.9%, which about 10-18 times higher than that of homopolymer in CHCl3 solution. Furthermore, the QE of two PA2TV-OXDs (purple fluorescence) are increased to 43.6 and 68.5%, respectively, about 1.3–1.4 times higher than that of PA2TV-Pys. Electrochemical results indicate that the electron affinity (Ea) of four alt-copolymers range from 2.79 to 3.09 eV, which are propitious to electrons injecting and transporting from the cathode. As a result, these novel copolymers present expected good electroluminescence(EL) performance in their single layer polymer light-emitting device (PLED) with configuration of ITO/polymer/Al, which turn-on voltages are between 4.0 and 5.8 V and emit bright green–yellow (538 nm) and yellow (545–552 nm) EL light. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

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