ELECTROPOLYMERIZATION OF CARBAZOLE IN MIXED ELECTROLYTE OF TETRAHYDROFURAN AND BORON TRIFLUORIDE DIETHYL ETHERATE

Abstract

The purpose of this work is to decrease the amount of boron trifluoride diethyl etherate(BFEE) usually used during the electrochemical polymerization and enhance the stability of as-formed polymer films.The mixed electrolyte of tetrahydrofuran(THF) and BFEE was used because THF can form a new complex with BF_3 which is more stable than BFEE and it also can be the solvent for many kinds of aromatic compound which can be electropolymerized.To increase the ionic conductivity of the mixed electrolyte,Bu_4NBF_4 was introduced.The ionic conductivity of THF containing 18% BFEE(by volume) and 0.1 mol·L-1 Bu_4NBF_4 was measured to be 1.25×10-3 S·cm-1.In this medium,high-quality polycarbazole(PCZ) films were electrosynthesized successfully by direct oxidation of 0.05 mol·L-1 carbazole.The oxidation potential of carbazole in this medium was measured to be only 0.92 V versus SCE,which was much lower than that determined in acetonitrile containing 0.1 mol·L-1 Bu_4NBF_4(1.36 V versus SCE).PCZ films obtained from this medium showed good electrochemical behavior,with electrical conductivity of 7.0×10-3 S·cm-1.As-formed PCZ films can be partly dissolved in strong polar organic solvents such as dimethyl sulfoxide.For dedoping,PCZ films were treated with 25% ammonia for 3 days.Then,they were dried at 60℃ for 24 h.The UV-Vis spectra of PCZ showed broader absorption bands mainly at 303 nm,implying wide molar mass distribution.In the fluorescence spectra,the emission peaks of polycarbazole appeared at 415 nm,implying the blue-light-emitting property of PCZ.The FT-IR and 1H-NMR spectral investigations of PCZ indicated that electrochemical polymerization of carbazole mainly occurred at 3,6 positions,in well accordance with the literature reported previously.Thermal analyses indicated that PCZ films prepared from this medium own good thermal stability.The successful electrosyntheses of PCZ films in this mixed electrolyte may extend the applications of this mixed electrolyte of THF,BFEE and Bu_4NBF_4 in the electrochemical science.