Preparation, optical properties, and electrochemical redox behavior of poly(benzimidazole-4,7-diy1)s are reported. Dehalogenation polycondensation of 4,7-dibromobenzimidaole and its derivatives (2heptyl and 2-phenyl derivatives) with zerovalent nickel complexes gives the corresponding po1ymer:s in 72-100% yield. Poly(benzimidazole-4,7-diyl) and its heptyl derivative have molecular weights of 1.3 x lo4 and 3.8 x lo4, 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 n-n* transition occurring in the benzimidazole monomeric unit, and another absorption peak at a longer wavelength, which is considered to originate from the n -~* transition occurring in the n-conjugated main chain. The n -~* 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.
'H NMR (CDCl3): 6 = 0.83 (t, J = 5.6 Hz, 3H, (3H3), 1.28
C~4Hd3rZNz
Calc. C44.9 H4.9 N 7.5 Br42.7 Found C45.0 H4.8 N7.6 Br43.0 2b can also be prepared from 1 (10 mmol) and 1-octyne (30 mmol) in tetrahydrofuran (THF, 20 cm3) by using a cata-