ESR and NMR studies of a novel conjugated donor-acceptor polymer containing magnetic spins: Poly [bicarbazolylene-alt-phenylene-bis(cyanovinylene)]

A conjugated alternating copolymer, poly[bicarbazolylene-alt-phenylenebis(e yanovinylene)] (named PCPV), was prepared via the Knoevenagel condensation in the presence of tetrabutylammonium hydroxide. Tetrahydrofuran-soluble lo w molecular weight materials and insoluble polymer were obtained. The two f ractions were characterized in detail by ESR and solid and solution NMR spe ctroscopies. Strong ESR signals were observed from the pristine PCPV polyme r in both fractions. This was explained by the rotational cleavage of the c is vinylic bond to produce two r radicals, called biradicals, which diffuse along the main chains to form radical cations stabilized by conjugation in the alternating repeating moieties. In particular, the insoluble fraction shows an extremely strong and sharp line width signal with a spin concentra tion equal to 5.8 x 10(17) spins/g. The alternating copolymer synthesized c an be considered as a novel conjugated material analogous to substituted po lyacetylenes with respect to the mobile unpaired electrons. The solid NMR s pectrum of the insoluble fraction of the PCPV copolymer is reported for the first time. By comparison with solution NMR studies of the soluble fractio n and of a model compound of the repeating unit, the structure of the copol ymer was established. The H-1 NMR spectrum of the soluble fraction allowed calculation of the DPn whose values roughly agree with that estimated by SE C measurements. However, the NMR signals of the soluble fraction were somew hat broadened because of the presence of unpaired electrons in the main cha ins.