The Synthesisand Properities Of Novel N-substituted Polyindoles

Indole is ubiquitous in biological and biochemical structure, and has attractedextensive interest in the construction of pharmaceuticals, fragrances, agrochemicals,dyes and materials in past decades due to its unique electrical, chemical, and opticalproperties. Along with the ever-increasing demand for polymer materials inindustries such as machinery and electronics, recently, considerable attentions havebeen devoted to the synthesis of indole-based polymers with peculiar properties aselectrochromic displays, batteries and conducting materials. Among the examplesreported, the most studied are polymerization of indole on its2,3-position through thesynthetic strategy of chemical oxidation or electrochemical polymerization, or formpendant indolyl groups on the polymer backbone. However, the examples illustratingpolyindole in which C-N bonding is present in the main chain are relatively few so far.To the best of our knowledge, there have never been attempts to prepare aromaticindole-containing high-performance polymer materials via nucleophilic substitutionpolycondensation reactions directly with the NH groups in indole moieties. Thecatalytic N-arylation of indole using transition-metal has become an importantsynthetic procedure for series of indole-based compounds. In view of some drawbacksin industrial applications of these transition-metal catalysts, such as expensive,oxygen sensitive, difficult to remove after the reaction and apt to leave toxic tracemetal contaminants. Therefore, the development of a mild and efficient method forconstructing N-arylindole motifs from indoles is highly desirable.Just under such a background, we developed a new polycondensation route forthe synthesis of novel indole-based polymers with precise structures. The catalyst-freenucleophilic substitution polycondensation of3,3’-Diindolylmethane with differentactivated difluoro monomers undergoes in N-methylpyrrolidinone (NMP), affordingpoly(N-arylene diindolylmethane)s (PMDINs) with high molecular weights (Mwup to479200) in high yields (up to95%). Model compounds were synthesized andcharacterized by standard spectroscopic methods in order to assist in the optimalreaction conditions for the polymerization of the polymers. Due to the indole moietiesin the main chains, all these PMDINs are endowed with significantly strong photonic luminescence in NMP.Due to the poor solubility and relatively lower molecular weights of PMDINs, Wepresent here a novel programmable polymerization route for the synthesis of newindole-based polymers via a catalyst-free nucleophilic substitution reaction. Thepolycondensation of4-hydroxyindole with different activated difluoro monomersundergoes in N-methylpyrrolidinone (NMP) to afford poly(N-aryleneindole ether)s(PEINs) with high molecular weights in high yields. The structures of the polymers arecharacterized by means of FT-IR,1H NMR spectroscopy and elemental analysis, theresults show a good agreement with the proposed structures. The resulting polymers areprocessable and exhibit high glass transition temperatures, good thermal stability andreasonable solubility. The amazing mechanical behavior, optical transparency as wellas excellent radiation resistance of the PEINs films suggest that they can be consideredas a new class of high-performance polymers. In addition, due to the indole moieties inthe main chains, all these PEINs are endowed with significantly strong photonicluminescence in chloroform and display a highly solvent-dependent emission band.Especially, the polymer PEIN-3carraying sulfonyl units shows outstanding blue-lightemission with high quantum yields.