π-Conjugated polymers based on indigo unit were prepared. Dehalogenative polycondensation of
N-hexyl-6,6'-dibromoindigo with a zerovalent nickel complex gave a homopolymer,
P(HexI), in 77% yield. Copolymer of
N-hexyl-indigo and pyridine,
P(HexI-Py), was also prepared in 50% yield.
P(HexI) showed good
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π-Conjugated polymers based on indigo unit were prepared. Dehalogenative polycondensation of
N-hexyl-6,6'-dibromoindigo with a zerovalent nickel complex gave a homopolymer,
P(HexI), in 77% yield. Copolymer of
N-hexyl-indigo and pyridine,
P(HexI-Py), was also prepared in 50% yield.
P(HexI) showed good solubility in organic solvents, whereas
P(HexI-Py) was only soluble in acids such as HCOOH. The weight-average molecular weights (
Mw) of
P(HexI) and
P(HexI-Py) were determined to be 10,000 and 40,000, respectively, by a light scattering method. Pd-catalyzed polycondensation between 6,6'-dibromoindigo with
N-BOC (BOC =
t-butoxycarbonyl) substituents and a diboronic compound of 9,9-dioctylfluorene afforded the corresponding alternating copolymer,
P(BOCI-Flu), as a deep red solid in 98% yield.
P(BOCI-Flu) was soluble in
N-methyl-2-pyrroridone and showed an
Mw of 29,000 in GPC analysis. Treatment of
P(BOCI-Flu) with CF
3COOH smoothly led to a BOC-deprotection reaction to give an insoluble deep green polymer,
P(I-Flu), in a quantitative yield. Diffuse reflectance spectra of powdery
P(BOCI-Flu) and
P(I-Flu) showed peaks at about 580 nm and 630 nm, respectively, which are thought to originate from the indigo unit.
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