ELECTROCHEMISTRY OF CHIRAL POLYANILINE IN IONIC LIQUIDS

摘要

The electrochemical behavior and chiroptical properties of electrodeposited chiral PAn.(+)-HCSA emeraldine salt films {HCSA = (+)-10-camphorsulfonic acid} have been investigated in a variety of ionic liquids {1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF_6), 1-butyl-3-methylimidazolium tetrafluoroborate (BMI-BF_4), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI), and (+)- or (-) and (+ -) -alpha-methylbenzylethylamine bis(trifluoromethyl sulfonyl)imide (MBEA-TFSI)} using cyclic voltammetry and in situ electrochemical UV-visible and circular dichroism spectroscopy. The electroactivity of the PAn.(+)-HCSA films was generally retained over a wide potential range. Although electrochemical degradation of the polyaniline films occurred in EMI-TFSI and MBEA-TFSI when they were held at high positive potentials (> +1.1 V), no evidence of degradation or chemical modification of polyaniline was observed when polarized at +2.0 V in BMI-BF_4. Surprisingly, racemisation of the polyaniline films occurred in all of ionic liquids when they were held at negative potentials, except in chiral or racemic MBEA-TFSI. Racemisation is attributed to incorporation of the cation from the ionic liquid during the reduction (rather than expulsion of the (+)-CSA anion) and resultant swelling of the polymer film. These results open the way to the future exploration of electrochemical asymmetric synthesis using such chiral polyanilinemodified electrodes and appropriate ionic liquids.