Novel fluorescent carbazolyl-pyridinyl alternating copoloymers: Synthesis, characterization, and properties

A novel series of AB-type polymers comprised of alternating carbazolyl and pyridinyl units were synthesized using palladium(O)-catalyzed Suzuki cross-coupling reaction in good to high yields. In this series of alternating copolymers, the electron-rich 2,7-(N-(2-ethylhexyl)carbazolyl) unit was used as a light-emitting unit, and the electron-deficient unit of pyridinyl was introduced to tune the wavelength of the emitting light and improve their electron transportation. These polymers were characterized by H-1 NMR and C-13 NMR, gel permeation chromatography (GPC), thermal analysis, UV-vis, fluorescence spectroscopy, and cyclic voltammetry (CV). The glass transition temperature of these polymers ranged from 120 to 150 degrees C, and the polymers showed high thermal stability with decomposition temperatures in the range 370-400 degrees C in nitrogen. The different linkage pattern of pyridinyl units in the copolymer backbone has a significant effect on the electronic and optical properties in solution and in film phases. For pure blue emission and prevention of aggregation of polymer chain, the meta-linkage pattern (3,5-and 2,6-linkage) of pyridinyl units in the polymer backbone is more favorable than the para-linkage pattern (2,5-linkage) of the pyridinyl units. The cyclic voltammetry (CV) results indicate that these polymers with pyridinyl units possess lower LUMO energy levels for an easy electron injection from a cathode than poly [3,6-(N-octyl)carbazolyll and its derivatives do.(7a)