Synthesis and characterization of a helical step-ladder polyarylene

A helical step-ladder polyarylene incorporating chiral (R)-2,2'-dioctoxy-1,1'-binaphthyl units was synthesized for the first time. The first step involved the preparation of a precursor poly(arylene ketone) via a palladium-mediated Suzuki-type cross-coupling reaction with the aid of microwave heating. Two polymer-analog reaction steps, the reduction of the keto groups to tertiary alcohol functionalities and subsequent intramolecular Friedel-Crafts cyclization, gave a step-ladder polymer (6) in good yields with reasonable mean average molecular weights greater than 13,000. The regioselective cyclization pattern in the alpha position of the naphthalene core was confirmed by a comparison of the NMR data of the polymer with those of the corresponding model ladder oligomers, 12 and 13, and also a single-crystal structure of 13. The optical spectra of the oligomers and polymers indicated that there was little electronic interaction across the binaphthyl units. The circular dichroism spectrum of 6 exhibited a strong hisignate Cotton effect in the pi-pi* absorption region of the planar chromophores, which reflected the strong exciton coupling within the helical polymer chain. (c) 2006 Wiley Periodicals, Inc.