Synthesis of indole-based functional polymers with well-defined structures via a catalyst-free C–N coupling reaction

Abstract

Poly(N-arylene diindolylmethane)s (PMDINs) with precise structures and high molecular weights (M_w up to 389 200) in high yields (up to 95%) were synthesized by the catalyst-free nucleophilic substitution polycondensation of 3,3′-diindolylmethane with different activated difluoro monomers via a C–N coupling reaction process. A model reaction was carried out to assist in determining the optimal reaction conditions for the polymerization and to elucidate the chemical structures of the polymers. The resulting polymers exhibited good thermal stability with high decomposition temperature (T_5% ≥ 377 °C). Fluorescent spectral studies indicated that all these PMDINs had strong solid-state fluorescence. Especially, the polymer PMDIN-3 carrying sulfonyl units was a good blue-light emitter with high quantum yields (21.6%, determined against quinine sulfate). The results obtained by cyclic voltammetry suggested that PMDINs possessed good electroactivity. In addition, owing to the electrochemical activity of the indole rings at the 2-position, PMDIN-3 was readily cross-linked by electrochemical oxidation and the cross-linking film was characterized by scanning electron microscopy. High molecular weights and good comprehensive performance of the indole-based polymers suggested that the catalyst-free C–N coupling reaction of indole derivatives with difluoro monomers could be considered as an effective polymerization route for the synthesis of new functional polymers with well-defined structures.