Electrosyntheses of high quality poly (5-cyanoindole) films in boron trifluoride diethyl etherate containing additional diethyl ether

High quality poly (5-cyanoindole) (P5CI) films were synthesized electrochemically by direct anodic oxidation of 5-cyanoindole on a stainless steel sheet in boron trifluoride diethyl etherate (BFEE) + 50% diethyl ether (EE) (v/v) + 0.05 mol L−1 Bu4NBF4. They can be peeled off the electrode into freestanding films. The introduction of EE to BFEE can improve the solubility of monomer. The oxidation potential of 5-cyanoindole in this medium was measured to be only 1.15 V versus SCE, which was lower than that determined in acetonitrile + 0.1 mol L−1 Bu4NBF4 (1.58 V versus SCE). BFEE + 50% EE + 0.05 mol L−1 Bu4NBF4 was tested to be a better medium than acetonitrile for the electrosyntheses of P5CI films. P5CI films obtained from BFEE + 50% EE + 0.05 mol L−1 Bu4NBF4 showed good electrochemical behavior, good thermal stability with conductivity of 10−2 S cm−1. The polymerization of 5-cyanoindole ring through 2,3-position was proved by FT-IR and 1H NMR spectroscopy. As-formed P5CI films were thoroughly soluble in strong polar organic solvent dimethyl sulfoxide (DMSO) while partly soluble in tetrahydrofuran (THF) or acetone. Fluorescence spectral studies indicated that P5CI was a good blue-light emitter.