Preparation and Chemical Properties of π-Conjugated Polymers Containing Indigo Unit in the Main Chain.

π-Conjugated polymers based on indigo unit were prepared. Dehalogenative polycondensation of -hexyl-6,6'-dibromoindigo with a zerovalent nickel complex gave a homopolymer, , in 77% yield. Copolymer of -hexyl-indigo and pyridine, , was also prepared in 50% yield. showed good solubility in organic solvents, whereas was only soluble in acids such as HCOOH. The weight-average molecular weights () of and were determined to be 10,000 and 40,000, respectively, by a light scattering method. Pd-catalyzed polycondensation between 6,6'-dibromoindigo with -BOC (BOC = -butoxycarbonyl) substituents and a diboronic compound of 9,9-dioctylfluorene afforded the corresponding alternating copolymer, , as a deep red solid in 98% yield. was soluble in -methyl-2-pyrroridone and showed an of 29,000 in GPC analysis. Treatment of with CF₃COOH smoothly led to a BOC-deprotection reaction to give an insoluble deep green polymer, , in a quantitative yield. Diffuse reflectance spectra of powdery and showed peaks at about 580 nm and 630 nm, respectively, which are thought to originate from the indigo unit.