Synthesis and Molecular Weight Dependent Optical Properties of Mono-Alkoxy Substituted Polythiophenes

Abstract

ABSTRACT:Poly(3-alkoxythiophene)s with moderately high molecular weights, which exhibit good solubility and film-forming ability, were successfully synthesized by the nickel (0) coupling reaction in good yields. The introduction of a branched side chain resulted in a molecular weight higher than that of the straight one. Broad photoluminescence (PL), ranging from 579 to 684 nm, was readily obtained by choosing the appropriate molecular weight sample of a mother polymer. This may provide a new method for evaluating organic luminescent materials.KEY WORDS Poly(3-alkoxythiophene) / Nickel Catalyst / Molecular Weight / Optical Properties / π-Conjugating polythiophenes have been considered promising candidates for polymer light-emitting diodes (LEDs), due to the tunability of emission colors, processability, and thermal and chemical stabilities. 1 Emission color closely depends on the extent of the effective conjugation along the backbone, which is mainly controlled by tailoring the structures of the main chain and side chain. 2, 3 Poly(alkoxythiophene)s are known to be useful as hole injection layers to improve the charge transport ability of LEDs, due to higher charge carrier mobility, lower oxidation potential, and better stability in the oxidized state, compared to alkyl substituted polythiophenes. 4 Although the synthesis of alkyl and di-alkoxy substituted polythiophenes has been well established, 5, 6 the synthesis of monoalkoxy substituted polythiophenes still remains a problem due to the low molecular weight and poor solubility. [7][8][9][10][11][12][13][14] This paper reports the synthesis and optical properties of three poly(3-alkoxythiophene) derivatives with moderately high molecular weights, which exhibit good solubility and film-forming ability. The introduction of a branched side chain in the monomer increased molecular weight of the polymer. These results may lead to a facile and inexpensive method for providing variable emission color by choosing the appropriate molecular weight samples of a single mother polymer. EXPERIMENTAL MeasurementsMolecular weights were evaluated by size exclusion chromatography (SEC) on a Shodex KF806 M column (eluent THF, 30 • C) in a Shimadzu liquid chromatography instrument equipped with a photodiode array detector based on the calibration using polystyrene stan- † To whom correspondence should be addressed.dards. Ultraviolet-visible (UV-vis) spectra (room temperature; 21 • C) were recorded on a JASCO V-570 spectrometer. Fluorescence spectra (room temperature; 21 • C) were recorded on a Hitachi F-850 spectrophotometer. NMR spectra were recorded on a Varian Unity 300 spectrometer relative to the TMS internal standard in chloroform-d. Materials3-Methoxythiophene was purchased from Aldrich Chemical Co. (R)-(−)-2-Octanol (≥ 99% e.e. (enantiomeric excess)) was purchased from AZmax Co., Japan. They were used without further purification. Monomer Synthesis3-Alkoxy substituted thiophenes were prepared by transetherification reaction between 3-methoxythiophene and corresponding pr...

Synthesis, characterization, and redox and electrochromic behaviors of poly(3‐n‐octyloxythiophene)

“…The wide peak of the 1 H-NMR spectrum was attributed to the four kinds of configuration triads: HT-HT, TT-HT, HT-HH, and TT-HH. 27 In the FTIR spectrum of POOT (Fig. 2), the bands at 2923, 2853, 1461, and 1374 cm 21 were contributed by the asymmetric, symmetric stretching, and out-of-plane deformations of CH 3 and CH 2 .…”

The Effects of Different Side Groups on the Properties of Polythiophene

“…The effect of the alkyl length on both molecular chain packing and the value of absorption maximum had been reported (1). Moreover, their optical properties (absorption maximum and visible photoluminescence color) were influenced by regulated by the change of molecular weight (MW) (7).…”

Effect of regioregularity and role of heteroatom on the chiral behavior of oligo(heteroalkyl thiophene)s

“…By contrast, the spectrum of PTOR* displays a broad resonance of the backbone 4-H proton at 7.02-6.80 ppm ( Figure S3B), upfielded with respect to the corresponding proton of PTSR*, as a consequence of increased electron density induced by the oxygen atom directly linked to thiophene ring. No accurate evaluation of the regioregularity degree can be made for PTOR*, as the resonances of the 4-H proton related to the four possible triad sequences (HT/HT, TT/HT, HT/HH, and TT/HH), reported as ranging in the intervals 7.04-6.84 ppm 35 or 6.95-6.83 ppm 36 for various poly (3-alkoxythiophene)s obtained under nonregiospecific conditions, are clearly overlapped. However, as the maximum intensity of the 4-H resonance of PTOR* is centered at 6.90 ppm, very close to the 6.91-ppm value reported for highly regioregular HT linkage in poly (3-decyloxythiophene) obtained by the same GRIM method, 37 we can conclude that PTOR* is characterized by highly predominant HT regioregularity.…”

“…The 1 H-NMR spectrum of PT2OR* ( Figure S4B) confirms the obtainment of a material having a substantially regiorandom structure, with the presence of three broad signals centered at 7.13, 6.97 (main), and 6.83 ppm, related, respectively, to the presence of prevalently HH/TT oligomers and to HH/TT/HT and HT/HT junctions. 35,36,38…”