Preparation and chemical properties of soluble π-conjugated poly(aryleneethynylene) consisting of azabenzothiadiazole as the electron-accepting unit

A soluble charge-transfer type poly(aryleneethynylene), PAE-AzaBzTdz, consisting of a highly electron-accepting azabenzothiadiazole unit was prepared in 99% yield by palladium-catalyzed polycondensation between 4,7-dibromo-2,1,3-azabenzothiadiazole (Br2-AzaBzTdz) and 1,4-diethynyl-2,5-didodecyloxybenzene. PAEAzaBzTdz showed a number-average molecular weight, M, of 6000 in gel-permeation chromatography analysis and had good thermal stability as measured by TGA. UV-vis spectrum of PAE-AzaBzTdz exhibited an absorption peak at 529 nm in chloroform, and the absorption peak shifted to a longer wavelength (601 nm) in film. Addition of MeOH to a CHCl3 solution of PAE-AzaBzTdz led to aggregation of the polymer to form stable colloidal particles. Results of filtration experiments using 0.2 and 0.02 mu m membranes supported aggregation of the polymer. Addition of trifluoroacetic acid (TFA) to a chloroform solution of PAE-AzaBzTdz led to a red-shift of the UV-vis peak from 529 to 640 nm. An X-ray diffraction pattern of powdery PAEAzaBzTdz indicated that the polymer assumed a layer-to-layer stacked structure with an interlayer distance of 3.4 A in the solid state. An X-ray diffraction pattern of cast film of PAE-AzaBzTdz revealed that the polymer molecules in the cast film were ordered on the surface of Pt plate with the dodecyl side chain oriented toward the surface of the Pt plate. (C) 2008 Wiley Periodicals, Inc.