Studies of dopant effects in poly(3,4‐ethylenedi‐oxythiophene) using Raman spectroscopy

Abstract

Raman spectroscopy has been used to study the doping processes in poly(3,4-ethylenedioxythiophene) PEDOT prepared via conventional electrochemical methods. The initially doped PEDOT films resulting from the polymerization process were first dedoped before being further oxidized in different electrolyte solutions at a number of different potentials to generate polymer films doped with a variety of dopants with different doping levels. Raman spectra of these re-doped PEDOT films were recorded ex-situ in order to monitor the progress of the re-doping processes by observing the shifts in the positions of CC stretching vibrations. This has provided an understanding of the extent of conversion between PEDOT structures from the dedoped state to the highly doped state during electrochemical re-doping. It was discovered that the extent of conversion varies with the type of dopant incorporated in the polymer films, which suggests that the doping process depends also on the nature of the dopant. Factors such as the size, the structural complexity and the charge on the dopant are believed to have significant effects on the efficiency of the doping processes in PEDOT. A curve-fitting method was also applied to fit the symmetric C a C b stretching band and its neighboring bands, in order to calculate the ratio of the band intensities due to the neutral and the oxidized structures in PEDOT. The doping level can then be approximately estimated by substituting this ratio into a previously determined correlation equation.

Controllable synthesis of leaflet-like poly (3,4-ethylenedioxythiophene)/single-walled carbon nanotube composites with microwave absorbing property

“…Thus the conductivity is elevated which is in agreement with the higher conductivity of PEDOT/SWCNTs in comparison to those of constituents as shown in Table 2. The similar results on shifting symmetric C a @C b stretching band with increasing polymerization potential have been discussed in previous reports, where the Raman band at 1414 cm À1 in the reduced PEDOT is shifted to 1445 cm À1 in the highly doped PEDOT [32][33][34]. The Raman band can be seen at 1363 and 694 cm À1 , which are assigned to C b AC b stretching and a CAH wagging component as well as symmetric CASAC ring deformation [30,35].…”

The electrochemical growth of conducting polymer “nanowires”

“…3). The main band at 1431 cm À1 has been assigned to C a = C b stretching on the five-membered ring of PEDOT [42,47]. It is widely accepted that three oxidation states exist for PEDOT: a neutral (undoped) state, a singly charged polaron state and a doubly charged bipolaron state, the latter two formed by oxidative doping [48], the ratio of the polaron to bipolaron concentration being determined by the dopant concentration and being reflected in the position of the Raman band around 1444 cm À1 .…”

A Dual Electrochrome of Poly‐(3,4‐Ethylenedioxythiophene) Doped by N,N′‐Bis(3‐sulfonatopropyl)‐4‐4′‐bipyridinium—Redox Chemistry and Electrochromism in Flexible Devices

“…A correlation of the quinoid with expanded coil conformation and that of the benzoid form with the compact coiled form has been reported. [31,32] The C b ÀC b stretching vibration [30] at 1362 cm À1 is only present in the film deposited at + 1.8 V. Furthermore, the C a ÀC a' inter-ring stretch frequency upshifts from 1247 to 1255 cm…”