2,5‐Dibromo‐3‐(6′‐hexylpyridine‐2′‐yl)thiophene (DBPyTh) was synthesized by the Suzuki coupling reaction between two aromatic compounds followed by the bromination. The Grignard metathesis reaction of DBPyTh with isopropylmagnesium chloride proceeded in 85% conversion and the regioselective halogen–metal exchange at the 2‐position was confirmed. Namely, 5‐bromo‐2‐chloromagnesio‐3‐(6′‐hexylpyridine‐2′‐yl)thiophene and 2‐bromo‐5‐chloromagnesio‐3‐(6′‐hexylpyridine‐2′‐yl)thiophene were generated in 90:10 molar ratio. Subsequently, the Kumada coupling polymerization was carried out using 1,3‐bis(diphenylphosphinopropane)nickel(II) dichloride to obtain poly(3‐(6′‐hexylpyridine‐2′‐yl)thiophene) (PolyPyTh). The polymer molecular weight could be roughly controlled by the catalyst concentration and the molecular weight distribution ranged from 1.25 to 1.80. The gas chromatograph analysis indicated that 5‐bromo‐2‐chloromagnesio‐3‐(6′‐hexylpyridine‐2′‐yl)thiophene was preferentially polymerized in 90% conversion and the percentage of the head‐to‐tail content (regioregularity) was calculated to be 96%. The matrix‐assisted laser desorption/ionization time‐of‐fright mass spectrum indicated that both polymer chain ends were substituted with the hydrogen atom. The absorption maxima of polymer in CHCl3 and thin film were observed at 447 and 457 nm, respectively, which were blue‐shifted compared with poly(3‐(4′‐octylphenyl)thiophene). From the CV measurement of the polymer thin film, highest occupied molecular orbital (HOMO) (−5.31 eV) and lowest unoccupied molecular orbital (LUMO) (−3.76 eV) energy levels were calculated from the oxidation and reduction onset potentials, respectively, and the electrochemical band gap energy was determined to be 1.62 eV. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
The Grignard metathesis reaction of 2,5-dibromo-3-(5 0 -hexylpyridine-2 0 -yl)thiophene (M1) with i-PrMgCl afforded 5bromo-2-chloromagnesio-3-(5 0 -hexylpyridine-2 0 -yl)thiophene (GM1) in the 86% selectivity. The Kumada coupling polymerization by Ni(dppp)Cl 2 gave polyM1 having the roughly controlled molecular weight between 6700 and 23,400. The characterization using the gel permeation chromatographic and matrixassisted laser desorption/ionization-time of flight mass spectra indicated the diffusion of the nickel catalyst from the propagating end. Based on the GC and 1 H NMR spectra, the head-to-tail content of polyM1 was calculated to be 89%. The regioselective Grignard metathesis reactions of 5,5 0 -dibromo-4-(5 00 -hexylpyridine-2 00 -yl)-2,2 0 -bithiophene (M2) and 5,5 0 -dibromo-4-(5 00 -hexyl-pyrimidine-2 00 -yl)-2,2 0 -bithiophene (M3) also occurred at the ortho-position of the nitrogen heterocycle. The Kumada coupling polymerizations gave polyM2 and polyM3 having the head-to-tail content of 75% and 85%, respectively. The UV-vis spectra of polymers suggested that the polymer conformation becomes more planar in the order of polyM1 < polyM3 < polyM2, which was investigated by the theoretical calculation of the model oligomers.
Poly[3-(5 0 -hexylpyridine-2 0 -yl)thiophene] (P3PT) (M n 5 13900, H-T content 5 90%) was prepared by the regioselective Grignard metathesis reaction and the subsequent Kumada coupling polymerization. Likewise, poly(3-hexylthiophene)-b-poly[3-(5 0 -hexylpyridine-2 0 -yl)thiophene] (P3HT-b-P3PT) (M n 5 17,300) was synthesized in the one-pot and successive monomer addition protocol, in which the segment ratio was calculated to be 56 (P3HT)/44 (P3PT) base on the 1 H NMR spectrum. The absorption and emission spectra of homopolymer P3PT(H), obtained by the protonation of the pyridine nitrogen, in THF/cyclohexane shifted to the longer wavelength as compared with those collected in THF, suggesting the aggregation in poor solvent. The aggregation of P3PT induced by the addition of Sc(OTf) 3 could be controlled by the molar ratio of pyridine and scandium complex. The protonated block copolymer P3HT-b-P3PT(H) was also subjected to the aggregate formation. The absorption maximum in THF/CH 3 OH showed a bathochromic shift and the fluorescence emission was almost quenched. From the 1 H NMR spectra and DLS measurements, P3HT-b-P3PT(H) forms nanometer scale aggregates particularly with the insolubility and stacking of non-ionic P3HT in alcohol as the driving force.
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