Efficient Synthesis Of Well-defined Polycarbazoles

Conjugated polymers are an attractive class of materials owing to their potentialapplications to organic electronic materials and devices. Among them, polycarbazoles（PCZ） are a well-studied class of polymers with good electrical and photoactiveproperties. The carbazole unit can be substituted at the3-and6-positions to yieldpoly（3,6-carbazole）s derivatives, as well as at the2-and7-positions to providepoly（2,7-carbazole）s derivatives, with different properties and potential applications.The former is mainly used in the field of application of electrochemical andfluorescence phosphorescence. Moreover, poly（2,7-carbazole）s derivatives has beenshown to have excellent optical properties in the range of visible light which is used inlight emitting diode. Therefore, the preparation of well-defined polycarbazoles is veryvaluable for the development of new functional materials.In this paper, we envision that the well-defined polycarbazole can be synthesizedvia the nickel catalyst transfer polycondensation. Through systematic study of thepolymerization parameters, the reaction conditions over preparation of poly（2,7-carbazole） and poly （3,6-carbazole） are optimized. To this end, we mainly do thefollowing.Firstly, after extensive literature research, conjugated polymers with lowpolydispersity have been successfully prepared via the nickel-catalyzed transferpolymerization, such as, polythiophene, polyphenylene, polypyridine, polypyrrole andpolyfluorene. We propose that the Ni-catalyzed transfer polycondensation is used forpreparation of poly （3,6-carbazole） and poly （2,7-carbazole）.Secondly,2,7-dibromo-9-octyl-9H-carbazole,2,7-dibromo-9-（2-ethyl hexyl）-9H-carbazole and2,7-dibromo-9-（heptadecan-9-yl）-9H-carbazole are chooosen as thestarting monomer to optimize the reaction condition. Through a large number ofcomparative experiments and analysis of results, we initially explored the factors ofN-alkyl side chains, catalysts, organomagnesium ate complexes, lithium chloride topolymerization reaction. After finding the optimal polymerization conditions,poly（2,7-carbazole） with molecular weight over20000and a low polydispersity indexof1.36was prepared and the structure of polymers is characterized by¹H NMR and¹³C NMR.Thirdly,3,6-dibromo-9-octyl-9H-carbazole and3-bromo-6-iodo-9-octyl-9H -carbazole are choosen as the starting monomer to optimize the reaction condition.Through a large number of comparative experiments and analysis of the results, weexplored the influence of catalysts, organomagnesium ate complexes and feed ratio ofthe monoer to the catalyst to polymerization reaction. Filtering out the optimalpolymerization conditions, poly（3,6-carbazole） with molecular weight over6000and alow polydispersity index of1.18was prepared and the structure of polymers ischaracterized by¹H NMR and¹³C NMR.Fourthly，based on the mechanism of Ni-catalyzed transfer polycondensationleading to well-defined poly（3-hexylthiophene） which was reported by Yokozawa andMcCullough, a possible mechanism is proposed to explain the reaction.