Using Cyclic Voltammetry, UV-Vis-NIR, and EPR Spectroelectrochemistry to Analyze Organic Compounds

In this article, we describe electrochemical, electron paramagnetic resonance, and ultraviolet-visible and near-infrared spectroelectrochemical methods to analyze organic compounds for application in organic electronics.

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These methods can help identify the effect of the molecular structure of electro-active organic molecules on charged carrier generations and dynamics, itemization potential, electron affinity, and bond graph values. These methods are a cheap and fast way to determine the most valuable parameters for many electro-active materials, without the need to construct special devices. The presented method can be used to analyze all types of electron active compounds, such as those with delocalized bi-electrons including small molecules and large polymeric chains.

To begin the CV procedure, fill a clean electrochemical cell with 1.5 milliliters of electrolyte solution and cap the cell with polytetrafluoroethylene electrode holder. Insert working auxiliary and reference electrodes into the cap with the working and reference electrodes as close together as possible without touching. Ensure that the electrodes are immersed in the electrolyte.

Then connect the electrodes to a potentiostat, being careful not to let the connectors touch each other. For a reduction analysis, bubble inert gas through the solution for at least five minutes to remove dissolved oxygen. Then raise the inert gas line above the solution and leave the gas flowing throughout the experiment.

Once the electrochemical cell is ready open the potentiostat software and select the CV procedure. Set the start potential to zero volts and set the upper and lower vertex potentials to two volts and zero volts for oxidation analysis, or to zero volts and negative 2.5 volts for reduction analysis. Set the stop potential to zero volts.

And the number of stop crossings to six. And the scan rate to 0.05 volts per second. Name the data file and acquire a voltammogram.

Check that the electrodes are clean and dissolved oxygen has been removed if applicable. Then add 10 microliters of a one millimolar furacin solution to the electrolyte and acquire a reference scan. After that, empty and clean the cell and the electrodes.

Fill the cell with 1.5 milliliters of a one millimolar solution of the compound to be analyzed in the electrolyte. Reconnect the cell to the potentiostat and sparge the solution if necessary. Then set the start potential to zero volts.

The upper and lower vertex potentials to 0.5 volts and zero volts for oxidation. Or zero volts and negative 0.5 volts for reduction. The stop potential to zero volts.

And the number of stop crossings to 10. And the scan rate to 0.05 volts per second. Name the data file and acquire this initial votammogram.

Then increase the upper vertex potential by 0.1 volt for an oxidation analysis or decrease the lower vertex potential by 0.1 volt for a reduction analysis. And run the scan again. Repeat this process until the full peak of interest is observed.

If successive scans have shifted potentials clean the reference electrode, let it soak in the electrolyte solution for one hour. And then repeat the measurement. After completing oxidation measurements, perform reduction measurements or vis versa.

Then set the start potential to zero volts, the upper vertex to one volt, the lower vertex to negative 2.7 volts, and the stop potential to zero volts. Run the scan and adjust the potential window as needed to ensure that the full peaks are visible. Repeat the process at different scan rates and in the presence of furacin.

To begin the UV-Vis near IR procedure fill a clean spectroelectrochemical cell with 0.5 milliliters of an electrolyte solution. Insert the working auxiliary and reference electrodes and place the assembled cell in the spectrometer. Connect the electrodes to the potentiostat and open the potentiostat and spectrometer software.

Take absorbance measurements on each detector as a solvent blank. Then disconnect, empty, and clean the cell. Refill it with either a one times 10 to the negative fifth molar solution of a compound in the electrolyte, or with the electrolyte alone if testing a material deposited on the working electrode.

It is very important to set up the spectroelectrochemical cell properly and in the way as similar as possible to the specrtroelectrochemical cell used to record the blank spectrum, only this will ensure the registration of good results. Place the cell in the spectrometer and reconnect the electrodes to the potentiostat. Apply a neutral potential to the cell and acquire a starting spectrum.

Increase the potential by 0.1 volt and wait about 10 seconds for the process to stabilize. Then acquire another spectrum. Continue this process until the first change is observed in the spectrum.

And then save that spectrum. Next, increase the potential by 0.05 volts. Wait for 10 seconds.

And acquire a spectrum. Repeat this process until the first or second oxidation potential, determined from the CV measurement, is reached. Then de dope the film by applying a neutral potential.

At the end, compare the spectra of the film before oxidation and after de doping. To begin the EPR spectroelectrochemistry procedure for polymeric materials deposited on a working electrode, fill the spectroelectrochemical cell with the electrolyte and place it in the EPR spectrometer. Set up the manganese standard and adjust the instrument parameters to cover only the third and fourth manganese lines.

Acquire a background spectrum, check for contaminants, and then remove and clean the cell. Next, refill the cell with the electrolyte. Place the electrodes in the cell with the reference and working electrodes inside the auxiliary electrode wire spiral, being careful not to damage the polymeric layer on the working electrode.

Position the working electrode close to the bottom of the cell and the reference electrode near the upper part of the active section of the working electrode. Connect the electrodes to a potentiostat and place the cell in the instrument. It is critical to set up spectroelectrochemical cell properly and not destroy definitive positives on the working electrode surface.

Incorrectly placing the working electrodes makes it impossible to register any results. Apply a neutral potential and acquire an initial spectrum. Then increase the potential by 0.1 volt, wait 10 seconds for the sample to equilibrate, and acquire another spectrum.

Repeat this process until the EPR signal appears. Then increase the potential by 0.05 volts, wait 10 seconds, and acquire another spectrum. Continue this process until the first or second oxidation potential is reached and then reverse the potential steps and return to the starting potential in the same way.

Then apply the potential at which the EPR signal appeared. Enable the manganese reference, and record a spectrum to obtain a measurement with the third and fourth spectral lines of manganese. The onset potentials of both reversible and irreversible processes can be estimated from calculations based on the intersection of lines tangent to the CV peaks with the background, adjusted for the reference material.

UV-Vis near IR spectroscopy of this polythiophene derivative show the neutral polymer absorption band diminishing and new polaronic and bipolaronic absorption bands forming during oxidative doping, with an isosbestic point at 604 nanometers. The new polaronic band from 550 to 950 nanometers was attributed to the radical cations of biothiophene and paraphenylene phenylene. A new bipolaronic band was observed between 950 and 1700 nanometers.

EPR spectroscopy during reduction of this S-tetrazine derivative showed a hyper fine splitting pattern that matched a simulation consistent with the interaction of an unpaired electron with the four nitrogen atoms of S-tetrazine. A single broad EPR signal is often observed from conjugated polymers, indicating significant de localization of the radical ion generated by the redux process of interest. While performing reduction analysis during this procedure be sure to properly de dope the solution before the measurement to avoid any interference from the self oxygen.

Following this procedure, the electron affinity ionization potential and band cap of the investigated material can be estimated from the data. By using this procedure you can determine the impact of chemical structure on the investigated properties for a group of materials.

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Journal (Chemistry)

Journal (Chemistry)

Using Cyclic Voltammetry, UV-Vis-NIR, and EPR Spectroelectrochemistry to Analyze Organic Compounds

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