In Situ Attenuated Total Reflection FTIR Spectroelectrochemistry Of Polybenzimidazobenzophenanthroline (BBL)
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sieve prior to measurement. Great precaution was taken in order to protect the electrolyte from atmospheric oxygen and water throughout the experiments. The chemical synthesis of BBL was reported elsewhere [8]. Thin films were prepared by spin coating from a solution of 0.8% BBL in gallium chloride/nitromethane onto glass substrates in laboratory atmosphere. The resulting polymer/Lewis acid complex film was washed with deionized water several times and subsequently placed in fresh deionized water overnight to remove the Lewis acid completely. Using a pair of tweezers the film was peeled off while still wet yielding a film floating on the water surface. The free standing film was then transferred onto a germanium reflection element covered with thin layer of evaporated platinum. The resulting solid film was dried in a vacuum oven for 6 hours at 800C. The in situ ATR-FTIR spectroelectrochemical measurements were carried out in a three-electrode spectroelectrochemical cell (figure 1) with a germanium working electrode, a platinum foil counter electrode, and a silver wire coated with silver chloride reference electrode. The electrolyte for the in situ spectroelectrochemical experiments was 0.1 M Bu4NClO4 in acetonitrile. The spectroelectrochemical cell was sealed with paraffin to prevent leakage of the electrolyte solution. The cell was placed in the FTIR cell compartment and the instrument was purged with nitrogen continuously throughout the experiment. A continuous flow system for the electrolyte was used where the electrolyte (placed in an external container where it was blanketed with argon after purging for few minutes) flows in and out of the electrochemical cell using teflon plastic tubes. To obtain n-doping, a potential scan between 0.6 V and -2.0 V with a scan rate of 5 mV s-1 using a sweep generator Prodis 1/14 I and a potentiostat Jaissle Model 1002 TNC was applied to the film. The cyclic voltammogram was recorded on an x-y recorder. During the scan, in situ FTIR spectra were recorded with a resolution of 4 cm-1 using Bruker IFS 66S spectrometer with an MCT detector. To obtain specific spectral changes during individual electrochemical reaction processes a spectrum just before the considered reaction was chosen as a reference spectrum. The subsequent spectra were related to the spectrum, showing only the spectral differences to this reference state. The spectra are plotted as ∆(-log(TATR)), where TATR is transmission in ATR geometry. For each spectrum 32 interferograms were coadded covering a range of about 90 mV in the cyclic voltammogram. The potential values given for each reference spectrum in this paper corresponds to the mean value of this range. Counter Electrode
O
O
N
N
N
N
BBL
n
Reference Electrode Electrolyte
IR beam
Detector
Ge reflection Element
BBL film
Figure 1. In situ ATR-FTIR spectroelectrochemical cell. Inset: BBL chemical structure.
RESULTS AND DISCUSSION The cyclic voltammetric response (CV) for the reduction (n-doping) and reoxidation (undoping) processes of BBL film is s
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