ELECTROCHEMICAL POLYMERIZATION OF FLUORENE HALIDE IN BORON TRIFLUORIDE DIETHYL ETHERATE SOLUTION

Abstract

Poly(9-bromofluorene)(PBF) films and poly(9,9-dichlorofluorene)(PDCF) films were electro-synthesized successfully by direct anodic oxidation of 9-bromofluorene(BF) and 9,9-dichlorofluorene(DCF) using a middle-strong Lewis acid boron trifluoride diethyl etherate(BFEE) as the solvent and the supporting electrolyte containing 0.02 mol/L BF and 0.05 mol/L DCF,respectively.The oxidation potential onset of BF and DCF in pure BFEE was 1.45 V versus SCE and 1.67 V versus SCE,respectively,which were much lower than those determined in acetonitrile containing 0.1 mol L-1 Bu_4NBF_4(BF,1.95 V versus SCE and DCF,2.19 V versus SCE).For spectral analysis,polymers were dedoped with 25% ammonia for 3 days.Then,they were dried at 60℃ for 24 h.For characterization of the structure and properties of as-formed polymers,UV-Vis,fluorescence,FT-IR,and 1H-NMR spectra of the polymers were determined.In the FT-IR spectra of BF or PBF,the peak at 650 cm-1 was the characteristic absorption of the C—Br bond.Three peaks at 819,759,737 cm-1 suggested that PBF was 1,2,4-trisubstituted.Similarly,the peak at 802 cm-1 was the characteristic absorption of the C—Cl bond in the IR spectra of DCF and PDCF.Additionally,the peaks at 867,731,829 cm-1 indicated that PDCF was also 1,2,4-trisubstituted.FT-IR and 1H-NMR spectral investigations indicated that electrochemical polymerization of BF and DCF mainly occurred at 2,7 positions.According to the UV-Vis spectra of the monomers,the UV-Vis spectra of PBF showed red-shfited absorption at 334 nm,and the PDCF showed broader absorption at 290 nm,342 nm,indicating higher conjugation length of backbone of the polymer.In the fluorescence spectra,the emission peaks of BF and DCF monomers appeared at 334 nm and 338 nm,respectively while those of PBF and PDCF in DMSO appeared at 396 nm and 537 nm,implying the blue-light-emitting property of PBF and the green-light-emitting property of PDCF.The main reason contributing to different light-emitting properties of PBF and PDCF was the electron-withdrawing effect of Cl and Br atoms.The electrical conductivity of PBF and PDCF films was measured to be nearly 10-1 S/cm.These semi-conducting and emitting properties will be greatly helpful for the applications of PBF and PDCF films.