Preparation and properties of π-conjugated poly(benzimidazole-4,7-diyl)s

Abstract

Preparation, optical properties, and electrochemical redox behavior of poly(benzimidazole-4,7-diyl)s are reported. Dehalogenation polycondensation of 4,7-dibromobenzimidazole and its derivatives (2-heptyl and 2-phenyl derivatives) with zerovalent nickel complexes gives the corresponding polymers in 72–100% yield. Poly(benzimidazole-4,7-diyl) and its heptyl derivative have molecular weights of 1.3 × 104 and 3.8 × 104, respectively, as determined by light scattering measurements. In non-acidic solvents the polymers give rise to one absorption peak at about 300 nm, which is assigned to a π-π* transition occurring in the benzimidazole monomeric unit, and another absorption peak at a longer wavelength, which is considered to originate from the π-π* transition occurring in the π-conjugated main chain. The π-π* absorption peak, as well as the photoluminescence peak of the polymers, are shifted in acidic media due to protonation. The polymers are electrochemically active regarding reduction (or n-doping) and show electrochromism.