Hydrolysis of doped conducting polymers

Abstract

Conducting polymers display a range of interesting properties, from electrical conduction to tunable optical absorption and mechanical flexibility, to name but a few. Their properties arise from positive charges (carbocations) on their conjugated backbone that are stabilised by counterions doped in the polymer matrix. In this research we report hydrolysis of these carbocations when poly(3,4-ethylenedioxy thiophene) is exposed to 1 mM aqueous salt solutions. Remarkably, two classes of anion interactions are revealed; anions that oxidise PEDOT via a doping process, and those that facilitate the SN1 hydrolysis of the carbocation to create hydroxylated PEDOT. A pKa of 6.4 for the conjugate acid of the anion approximately marks the transition between chemical oxidation and hydrolysis. PEDOT can be cycled between hydrolysis and oxidation by alternating exposure to different salt solutions. This has ramifications for using doped conducting polymers in aqueous environments (such as sensing, energy storage and biomedical devices).

A Fibre-Optic Platform for Sensing Nitrate Using Conducting Polymers

“…As the same PEDOT sample is exposed to CO , it switches to an even darker blue appearance, although the spectral difference is minuscule. The visible change in colour of the PEDOT layer is an indication of the polymers interaction with the surrounding aqueous solution [ 31 ]. Figure 2 b shows absorbance spectrum (400–2500 nm) of a thin layer (200 nm) of PEDOT prepared on the soda-lime silica glass before and after exposure to NO and CO for 2 min.…”

“…Na CO was used in solution at low concentration to achieve a pH of ∼10.5, in order to chemically reduce the PEDOT to a lower oxidation level. The details of this mechanism and its reversible nature were recently described by Sethumadahavan et al [ 31 ]. In comparison to commonly used NaOH and polyamide solutions, the Na CO solution is envisaged to lower the oxidation level of PEDOT without inflicting irreversible damage associated with strongly basic solutions [ 32 ].…”

“…Herein, the response time is defined as the exposure time to a particular analyte that is required to achieve a stable back reflection for two consecutive measurements in air after the fibre probe comes out of a particular analyte concentration, while in the above experiments, to make sure that the probe has been fully reset, we immersed the probe in CO after each NO exposure for 19 h. In order to see if it would be possible to have a shorten exposure time preliminary series of experiments were conducted. it appears that an initial step of 19 h exposure to CO to remove most of the tosylate [ 31 ] followed by a 2 min consecutive exposure to NO is sufficient to reset the probe to the same value of back reflection ( ). In all measurements, initially fibre probe coated with PEDOT dipped into CO solution (1 mM) for 19 h as a “resetting” step.…”

“…This reversible process is accompanied by changes in the optical properties of the PEDOT and typically exploited in electrochromic devices [ 28 , 29 , 30 ]. For the sensing device reported herein, NO is used as the dopant, with a basic solution (pH ≈ 10.5) of 1 mM CO used to chemically reduce the PEDOT [ 31 ] (similar to hydroxide [ 32 ] and polyamide solutions [ 33 ]) and thus resetting the sensing probe. The PEDOT doped with the Tosylate anion (PEDOT:Tos) is used to investigate oxidation and reduction (redox) switching in Milli-Q water.…”

2D and 3D Immobilization of Carbon Nanomaterials into PEDOT via Electropolymerization of a Functional Bis-EDOT Monomer

“…Therefore, it has been widely used in electronic applications and acceptors for organic photovoltaic devices (OPV) [ 24 , 25 , 26 , 27 , 28 ]. Analogously, carbon nanotubes (CNTs) are widely explored, due to their excellent electronic mobility [ 29 ], coupled with a high surface area, ultralight weight, electron-rich properties, and excellent chemical and thermal stability [ 30 , 31 ]. In contrast to C 60 , pristine CNTs are not soluble and possess very limited dispersibility.…”