New synthetic routes to poly (isothianaphthene) I. Reaction of phthalic anhydride and phthalide with phosphorus pentasulfide

A new route for the formation of the low bandgap polymer poly(isothianaphthene) is presented. The route comprises the reaction of phthalic anhydride or phthalide with phosphorus pentasulfide at elevated temperatures (T ⩾ 120 °C), and leads to the formation of poly(isothianaphthene) in one single step. The product obtained was analysed by elemental analysis, IR, Raman and solid state NMR spectroscopy. Chemical doping and dedoping of the material were investigated, and the maximum conductivity obtained was 10 S cm−1 by doping with NOSbF6. Both doped and undoped samples of poly(isothianaphthene) prepared by this new route were thermally very stable in air or in an inert helium atmosphere as shown by thermogravimetric analysis. Furthermore, the conductivity of a doped sample remained unchanged up to 250 °C in air. Preliminary results showed that the reaction with phosphorus pentasulfide can also be used to obtain nitrogen analogues of poly(isothianaphthene).