Low-potential electrochemical polymerization of 6-nitroindole and characterization of its polymers

Abstract

Conducting polymers bearing nitro substituents are very important from both academic and industrial viewpoints. However, it is very difficult to electrosynthesize such conducting polymers because of the strong electron-withdrawing effect of nitro groups. In this article, we describe the electrochemical synthesis of films of a new conducting polymer, high-quality poly(6-nitroindole) (P6NI), by direct anodic oxidation of 6-nitroindole in boron trifluoride diethyl etherate containing 10% (v/v) diethyl ether. The oxidation potential onset of 6-nitroindole in this medium has been measured to be just 0.98 V versus a saturated calomel electrode (SCE), which is much lower than that determined in acetonitrile containing 0.1 mol/L tetrabutylammonium tetrafluoroborate (1.6 V vs SCE). Thermal studies have revealed that P6NI displays good thermal stability. The electrical conductivity of the P6NI films has been measured to be 0.08 S/cm. Structural studies have shown that the polymerization of the 6-nitroindole ring occurs mainly at the 2,3-positions. Fluorescence spectral studies have shown that the principal excitation and emission peaks of P6NI are at 416 and 535 nm, respectively, with a fluorescence quantum yield of 0.05. All these properties of P6NI films may facilitate their potential applications in various fields, such as electrochemical sensors and green-light-emitting materials. To the best of our knowledge, this is the first report on the electrosynthesis and characterization of 6-nitro-substituted polyindole films. © 2007 Wiley Periodicals, Inc.