Synthesis and Properties of 1,8-Carbazole-Based Conjugated Copolymers

A new series of conjugated carbazole polymers based on the 1,8-carbazolylene unit was synthesized by the Pd-catalyzed polycondensation between the 1,8-diiodocarbazole derivative and various bifunctional counter comonomers. An alkyne spacer was found to be a key to increasing the molecular weight of the resulting polymers. All the obtained polymers showed good solubilities in the common organic solvents, and they were fully characterized by Gel permeation chromatography (GPC), and H-1 NMR and infrared (IR) spectroscopies. The UV-vis absorption and fluorescence spectra revealed the relationship between the chemical structure and effective conjugation length. The efficiency order of the carbazole connectivity was 2,7-carbazolylene > 1,8-carbazolylene > 3,6-carbazolylene. The electrochemical properties of these polymers suggested the relatively facile oxidation at ca. + 0.5-0.7 V vs. Fc/Fc(+) or a high potential as p-type semiconductors. The combination of the electrochemical oxidation potentials and the optical band gaps allowed us to estimate the HOMO and LUMO levels of the polymers. It was shown that the energy levels of the 1,8-carbazole-based conjugated polymers can be tunable by selecting the appropriate comonomer structures.