Name: raman and ir spectroelectrochemical methods as tools to analyze conjugated organic compounds
Uploaded: 2018-10-12T12:30:00
Duration: 9 min 11 s
Description: Watch this Scientific Journal Video about Raman and IR Spectroelectrochemical Methods as Tools to Analyze Conjugated Organic Compounds at JoVE.com

The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sk&#322;odowska-Curie grant agreement No 674990 (EXCILIGHT). We thank the networking action funded from the European Union's Horizon 2020 research and innovation programme under grant agreement No 691684.

1. Preparation of the Experiment
<ol>
	<li>Cleaning procedure24 
	NOTE: The typical spectroelectrochemical cell consists of a platinum mesh(wire) or ITO working electrode (WE), Ag/AgCl or Ag electrode as a reference electrode (RE) and platinum coil or wire as an auxiliary electrode (AE) (Figure 1). All electrodes must be cleaned before use.
	<ol>
		<li>Rinse a quartz ITO electrode with deionized water from the wash bottle. Then place it in an ultrasonic bath in a beaker filled with acetone for 15 minutes at room temperature and then in a beaker filled with isopropanol for the next 15 minutes. The higher ultrasound bath power that is used, the better result of cleaning.</li>
		<li>Let the electrode dry in the air.</li>
		<li>Burn platinum mesh or wire working electrode using a high-temperature torch (at least 500 &#176;C) until it gets red (approximately 1 min). Remove it from the fire, when it turns red and then cool it in the air to room temperature (approximately 1 min). Be careful to not melt the mesh electrode.</li>
		<li>Polish the gold working electrode with emery paper (grit 2000) and then with 1 &#181;m alumina. Ultrasonicate in deionized water for 5 minutes. Afterwards, rinse the electrode three times with the solvent used for the measurements. Use working electrodes directly after cleaning.</li>
		<li>Burn the active area of the auxiliary electrode (platinum wire or spiral) using a high-temperature gas torch (at least 500 &#176;C) until it gets red (approximately 1 min) and then cool in the air to room temperature.</li>
		<li>Take the reference electrode out from the storage electrolyte and wash it three times with the solvent used for the measurements.</li>
		<li>Clean the spectroelectrochemical vessel with alcohol (ethanol or isopropanol) or acetone using a syringe and air dry. Clean all other elements (i.e., Teflon parts) with acetone and air dry before use (minimum 1 minute).</li>
	</ol>
	</li>
	<li>Prepare at least 10 mL of the supporting electrolyte solution. The electrolyte solution should fulfil the same requirements as for standard electrochemical experiments, i.e., its concentration should be at least 100 times higher than the concentration of the analyte. An example electrolyte could be 0.2 M solution of Bu4NPF6 in dry acetonitrile or dichloromethane and a sample concentration of 1 mM. Water solutions, like 1 M H2SO4(aq), can be also used for Raman spectroscopy. If it is possible, use solvent and electrolyte of the highest purity.</li>
	<li>In the case of spectroelectrochemistry of an analyte present in solution, prepare at least 1 mL of an analyte solution at 1 mM concentration in the electrolyte solution.</li>
	<li>Put the argon (or nitrogen) Teflon pipe in the solution and start bubbling it for at least 5 min, in order to remove residual oxygen from the solution. Control the gas flow, so that only small bubbles appear at the solution surface. Do not use too high gas flow; otherwise, the solvent will evaporate from the vessel. In order to reduce solvent evaporation, a gas saturated with the solvent can be used. In this case, the inert gas must flow through a container with dry solvent before flowing to your electrolyte solution.</li>
</ol>
2. IR Spectroelectrochemistry
<ol>
	<li>Run electrochemical (cyclic voltammetry) tests on the analyte before starting the spectroelectrochemical analysis7, so that the potential range, in which the redox processes occur, or the reversibility of the redox processes, can be determined.</li>
	<li>Assemble the experimental cell equipped with three electrodes (working mesh platinum, auxiliary and reference) as presented in Figure 1. Ensure there is no leakage by filling it with the pure solvent. In the case of leakage, correct the mounting of the cell. When the cell is tight, remove the solvent with the syringe.</li>
	<li>Turn on the IR spectrometer and the corresponding software.</li>
	<li>Put the cuvette in the spectrometer holder. Fill the cuvette with the 2 mL of the analyte solution. The part of the working electrode, that will be irradiated with the incident beam, and the reference and auxiliary electrodes must be immersed in with the solution.</li>
	<li>Connect the electrodes with corresponding wires going from the potentiostat using crocodile clamps. Ensure to not short circuit the electrodes (they should not touch each other).</li>
	<li>Set the parameters of the spectra acquisition (spectrum range and resolution, the number of spectra to repeat in the case of FTIR). An example of typical parameters are as follows: spectrum range of 600-4000 cm-1, resolution of 1 cm-1, the number of spectra to repeat &#8211;&#160;16.</li>
	<li>Collect the IR spectrum by pressing the corresponding button on the spectrometer or in the software. Here, press the Background button to register a background and then press Scan button to collect spectrum.</li>
	<li>Using the connected potentiostat apply a potential of 0.0 V to the working electrode and collect the IR spectrum (press the Scan button). Save the spectrum giving it an appropriate filename.</li>
	<li>Change the applied potential, typically increase by a 100 mV, wait for app. 5 s, collect another IR spectrum and save it under the appropriate filename. Repeat this step until you reach entire potential range, in which oxidation/reduction processes may occur.</li>
	<li>In order to check the reversibility of the structural changes during electrochemical oxidation or reduction, return to an initial potential (0.0 V) and collect the IR spectrum again. Either apply an increment of 100 mV or go straight back to the initial potential.</li>
	<li>Subtract the initial spectrum from all other spectra to obtain differential spectra. Then, determine a straight line as the baseline by subtracting the neutral spectrum from itself in the software.
	<ol>
		<li>From the menu Process, chose Arithmetic.</li>
		<li>In the newly opened window (Arithmetic settings), chose the operator from the dropdown list Subtract (-).</li>
		<li>Select Operand and then select the spectrum registered at 0.0 V from the dropdown list.</li>
		<li>To confirm the operation, press OK.</li>
		<li>To export data to a spreadsheet, choose File | Send To | Excel.</li>
	</ol>
	</li>
	<li>When finishing the spectroelectrochemical measurement, register a CV of the solution (refer to point 2.1 of the protocol). Then add the appropriate amount of ferrocene to receive its concentration of app 0.5 mM and register the CV again. 
	NOTE: Ferrocene is used as a standard as its oxidation potential occurs at 4.8 eV. By recalculating the oxidation/reduction potentials of the sample vs. ferrocene, estimate the proper potential of the registered process and unify your data.</li>
</ol>
3. IR Spectroelectrochemistry in a Reflectance Mode
<ol>
	<li>Perform the same measurement procedure as for the transmission mode. The only difference is in the cell assembly (2.4) which is different for each kind of experimental cell.</li>
</ol>
4. Raman Spectroelectrochemistry
<ol>
	<li>Run the electrochemical (cyclic voltammetry) tests on the analyte before starting the spectroelectrochemical analysis7, so that the potential range, in which the redox processes occur, or the reversibility of the redox processes, can be determined.</li>
	<li>Deposit the layer of interest on the wire or plate electrode by electrochemical polymerization or by dip casting method12.</li>
	<li>Turn on the Raman spectrometer, laser and the corresponding software.</li>
	<li>Put the experimental cell together. Place the three electrodes (working, reference and auxiliary) in the cuvette, so that they do not touch each other, as presented in the Figure 2. The best is to use a Teflon holder, well-fitting the cuvette.
	<ol>
		<li>Place the working electrode (or working electrode covered with the deposited film) as close to the cuvette wall facing the incoming incident beam as possible, but do not press it to the wall (leave some space so the solution can flow easily between the cuvette wall and the working electrode).</li>
	</ol>
	</li>
	<li>Fill the cuvette with the electrolyte or analyte solution using a syringe (approximately 2 mL). Immerse all electrodes in the solution.</li>
	<li>Put the cuvette into the holder in the Raman spectrometer and connect the electrodes with corresponding wires going from the potentiostat using crocodile clamps. Ensure that electrodes or connectors do not touch each other.</li>
	<li>If the spectrometer is equipped with a camera, focus it onto the film deposited on the working electrode manually and/or using the software. A clear view of the working electrode surface should be visible.</li>
	<li>Close the spectrometer&#39;s cover.</li>
	<li>Choose the type of the laser desired and the corresponding grating based on the literature data or self-experience (for example the near infra-red 830 nm excitation laser and 1200 lines grating can be used). 
	NOTE: The higher energy of the incident beam light the more accurate spectra can be obtained, but also the greater risk of fluorescence, which prevents spectrum analysis. The choice of the grating type will change the range and/or resolution of acquired spectra. Typically, the most appropriate laser and grating can be selected by testing all available.</li>
	<li>Focus the laser beam on the working electrode surface using the software. If the spectrometer is equipped with a camera, the position at which the sharpest dot or line of the incident beam light on the sample is observed.</li>
	<li>Set the parameters of the spectra acquisition: laser power, spectral range, time of illumination of the sample etc. The choice of the parameters depends on the type of the film or/and the substrate and should be selected individually. Do not use too high laser power; otherwise the sample is destroyed. Example parameters are as follows: laser power - 1%, spectra range - 400-3200 cm-1, time of illumination - 1 s, measurement repeated 3 times.</li>
	<li>Collect the Raman spectrum by pressing the corresponding button on the spectrometer or in the software. If the intensity of the peaks on the registered spectra is weak, increase the power or acquisition time. A broadband in the spectra indicates the fluorescence phenomena. In this case, change the incident beam light to less energetic (higher wavelength) or try decreasing the laser power.</li>
	<li>Apply a potential of 0.0 V to the working electrode using the connected potentiostat and collect the Raman spectrum. Save the spectrum giving it an appropriate filename.</li>
	<li>Change the applied potential, typically increasing by 100 mV, wait for approximately 15 s, collect another spectrum and save it under the appropriate filename. Repeat this step until reaching the entire potential range where oxidation/reduction processes occur.</li>
	<li>In order to check the reversibility of the structural changes during electrochemical oxidation or reduction, return to the initial potential (0 V) and collect Raman spectrum again.</li>
	<li>When the spectroelectrochemical measurements are finished, register a CV of an analyte (present in solution or deposited on the electrode). Then, in the case of aprotic solutions, add the appropriate amount of ferrocene to obtain its concentration of app 0.5 mM and register the CV again. 
	NOTE: Ferrocene is used as a standard, as its oxidation potential occurs at 4.8 eV. By recalculating the oxidation/reduction potentials of the sample vs. ferrocene, the proper potentials of registered processes can be determined.</li>
</ol>

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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Raman+Spectroelectrochemistry+of+a+Lithium/Polymer+Electrolyte+Symmetric+Cell.">Raman Spectroelectrochemistry of a Lithium/Polymer Electrolyte Symmetric Cell.</a> J Electrochem Soc. 145, 3034-3042 (1998).</li><li>Adar, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Depth+Resolution+of+the+Raman+Microscope:+Optical+Limitations+and+Sample+Characteristics.+Spectroscopy.">Depth Resolution of the Raman Microscope: Optical Limitations and Sample Characteristics. Spectroscopy.</a> Spectroscopy. , (2018).</li></ol>

The authors have nothing to disclose.

Both IR and Raman techniques are recommended for the investigation of the structural changes occurring under applied potential and for the investigation of the products of the redox reaction. However, from the practical point of view, Raman spectroscopy is handier as an analytical tool in such experiments. Raman spectroelectrochemistry gives more possibilities, as it can be also applied to samples with nonpolar bonds. It has been therefore successfully used for the investigation of carbon materials, polymers, batteries, etc.29,30,31,32,33 Since the scattered light is measured substantially in Raman spectroscopy, there are generally no limits in the working electrode material or construction. Additionally, as used herein, incident light (UV-Vis-NIR) is poorly absorbed by the glass, which allows for the use of a standard electrochemical cell. The great advantage is also the possibility of conducting measurements outside the spectrometer through fiber optics. In order to register a Raman spectrum, the incident light needs to be properly focused on the sample. By focusing the light beam at different locations of the measuring cell, it can be decided if the changes in chemical composition occurring in the solution, e.g. near the electrode, or in the species adsorbed on the electrode surface are followed.
The use of Raman spectroscopy with an appropriate resolution also allows for the study of the profile of the solid samples, either on the surface or in its depths, also in the multi-layer structures.34,35,36,37 One can, therefore, get information about the surface topography, the distribution of different chemical species at the surface or in cross-section. Raman spectroelectrochemistry permits in situ tracking of the changes of all these features during redox processes and thus estimate the quality of the individual layers, the durability of the system during multiple oxidation/reduction cycles, or studying the diffusion in multilayer structures. The versatility of Raman spectroelectrochemistry lies in the fact that it can be used to examine both the electrochemical processes in a solution or solid state in a typical experimental cell or even test multilayer solid structures like LEDs, batteries, OPVs, etc.
The undoubted disadvantage of Raman spectroscopy and, thus also spectroelectrochemistry, is its limitation due to observed fluorescence, which often makes it impossible to analyze the spectrum. This phenomenon can be in some cases eliminated by changing the excitation wavelength or preliminary illumination - photo-bleaching.

The combination of electrochemical and spectroscopic techniques allows for the possibility of tracking the structural changes in molecules present at the electrode surface or in the solution, thus investigating the mechanism of the electrochemical processes. Spectroelectrochemical methods are typically used for the in situ study of the mechanism of the reaction. The undoubted advantage over ex situ measurements is the possibility of observing the signal arising for the intermediate products of processes or investigating the processes, in which products cannot be separated1. Among all spectroscopies, the Raman and infrared spectroscopies are the most powerful for analysis of electrochemical processes due to equipment availability and the often non-destructive nature of the measurements.
Infrared and Raman spectroscopies provide information about the vibrational structure of the species and thus the existing chemical bonds. Since the nature of the signals observed in both techniques is different, some vibrations may be active only in IR or Raman spectra, making them complementary to each other2. This should be taken into account, when planning spectroelectrochemical analysis and, if possible, the vibrational structure of an analyte should be examined using both IR and Raman spectroscopies. The best results are obtained when the changes in the structure are the result of the electrochemical process involving groups active in the certain technique. For example, the infrared spectroscopy would be ideal for processes involving -CO, -CN -NO or -NH groups&#39; formation or breakage3. It is always recommended to register differential spectra of the spectroelectrochemical investigation. Also, such spectra disclose changes in the signals with lower intensity allowing the tracking of changes in the structure of the aromatic systems. Additionally, differential spectra are always less complex as only changes are registered, which makes the interpretation of the spectra much easier.
IR spectroelectrochemical experiments are mainly used for the monitoring of the soluble products, intermediates and reactants of the electrochemical reactions; such tests may be run on various systems, including organic, inorganic, or biochemical systems3,4,5,6,7,8. One should always remember that in the case of IR spectroscopy, solvents in which hydrogen bonding occurs, like water, should be avoided.
There are several ways to proceed with IR and Raman measurements. In the case of IR spectroscopy, measurements can be done in the transmission mode, in which conventional IR cuvettes for liquids can be used. The optically transparent electrodes (e.g., boron-doped diamond electrode) or perforated electrodes (metal gauze working electrode) made of fine metal (Pt or Au) are usually used as the working electrodes in such transmission cells4,9. An example of the transmission spectroelectrochemical cell is presented in the Figure 1.
In the second technique, instead of transmission, the reflectance mode is applied, thanks to the ATR (Attenuated Total Reflection) attachment10. This method allows analyzing both solutions and solid-state materials. Typically when using the method of external reflection absorption spectroscopy, in principle, any working electrode can be used, but only dissolved species can be investigated. However, in some cases, the ATR technique allows also for the investigation of processes in the solid state, using the internal reflection method5,8. A special cell is required for this technique, in which the fine metal sputtered on the ATR crystal acts as a working electrode (Figure 2). In some cases, even the ATR Ge crystal itself can act as an electrode (at least for not too high currents)5.
The second technique is Raman spectroelectrochemistry; a technique combining both electrochemistry and Raman spectroscopy, commonly used in the investigation of the potentially-induced structural changes in the deposited layer of conjugated polymers11, like polyaniline12, polypyrroles13, polycarbazole14 or PEDOT15. Additionally to polymeric films, monolayers can be also tested19,20,21, though in this case metallic substrates, like gold or platinum, are preferred. The procedure of Raman spectroelectrochemical studies is analogical to other spectroelectrochemical techniques, i.e., a spectrometer must be coupled with a potentiostat and the spectra of the film are acquired in the potentiostatic conditions under various potentials&#39; applied18. Typically, the three-electrode spectroelectrochemical cell can be constructed based on the classical quartz cuvette with electrodes mounted in a Teflon holder (Figure 3). The acquisition parameters, like the type of the laser, grating, etc., depend on the properties of the investigated layer. Selection of some parameters can be quite difficult, e.g., one has to remember that various excitation wavelengths can result in different spectra. Usually, the higher energy of incident light the more details are visible on the spectrum, but also the higher risk of fluorescence phenomena that hinders the analysis. Generally, it is very useful to obtain the UV-Vis-NIR spectra of the analyte at first, in order to select the Raman excitation laser. The tunable lasers can be adjusted so that the excitation wavelength induces coincidence with an electronic transition of the molecule, resulting in the resonance Raman scattering. In this case, the increasing Raman scattering intensity in chosen regions of the spectra or even formation of new signals is observed that would not be registered typically. The analysis of the structural changes consists in the assignment of recorded Raman bands, which can be done based on the literature data or DFT simulations23.

<table border="0" cellpadding="0" cellspacing="0" width="595">
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			<td height="42" style="height:42px;width:216px;">Potentiostat</td>
			<td style="width:85px;">Metrohm</td>
			<td style="width:127px;">Autolab PGSTAT100</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Raman microscope</td>
			<td style="width:85px;">Renishaw</td>
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			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">FT-IR Spectrometer&#160;</td>
			<td style="width:85px;">PerkinElmer&#160;</td>
			<td style="width:127px;">Spectrum Two&#160;</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Bu4NBF4</td>
			<td style="width:85px;">Sigma-Aldrich</td>
			<td align="right" style="width:127px;">86896</td>
			<td></td>
		</tr>
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			<td height="42" style="height:42px;width:216px;">DCM</td>
			<td style="width:85px;">Sigma-Aldrich</td>
			<td align="right" style="width:127px;">443484</td>
			<td></td>
		</tr>
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			<td height="42" style="height:42px;width:216px;">Isopropanol</td>
			<td style="width:85px;">Sigma-Aldrich</td>
			<td align="right" style="width:127px;">675431</td>
			<td></td>
		</tr>
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			<td height="42" style="height:42px;width:216px;">Acetone</td>
			<td style="width:85px;">Sigma-Aldrich</td>
			<td align="right" style="width:127px;">439126</td>
			<td></td>
		</tr>
	</tbody>
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raman and ir spectroelectrochemical methods as tools to analyze conjugated organic compounds

In the presented work, two spectroelectrochemical techniques are discussed as tools for the analysis of the structural changes occurring in the molecule on the vibrational level of energy. Raman and IR spectroelectrochemistry can be used for advanced characterization of the structural changes in the organic electroactive compounds. Here, the step-by-step analysis by means of Raman and IR spectroelectrochemistry is shown. Raman and IR spectroelectrochemical techniques provide complementary information about structural changes occurring during an electrochemical process, i.e. allows for the investigation of redox processes and their products. The examples of IR and Raman spectroelectrochemical analysis are presented, in which the products of the redox reactions, both in solution and solid state, are identified.

The structural changes of the monomer and polymer occurring during the doping are very useful to determine the mechanism of the process and for that, the IR spectroelectrochemical investigation can be conducted (Figure 4). In the example experiment, IR spectra were recorded in the differential form i.e. IR spectra of the investigated compound were taken as a reference. Such an approach allows for the exposure of the changes in the spectra occurring during polymerization: the disappearance of bonds are thus seen as a positive signal (increasing transmittance) while the formation of the new bonds is seen as negative peaks (decreasing transmittance) (Figure 4).
IR spectra recorded during analyte electropolymerization are shown in the Figure 4. As it can be seen, some changes occur at around 1600 cm-1, suggesting the disappearance of some of the material&#39;s double bonds. The most important are changes in the region between 700 - 900 cm-1: the increase in the transmittance at 750 and 675 cm-1 indicates the disappearance of the monosubstituted ring, simultaneously a new signal arising from the disubstituted ring appears around 830 cm-1. Based on the presented IR spectroelectrochemical experiment, the mechanism of the electropolymerization consisting in the reaction of the vinyl group with the free benzene ring is proposed.
In the presented example of Raman spectroelectrochemical studies, the potentially-induced structural changes of polyaniline film deposited on the electrografted layer of aniline (Figure 5) are investigated. The Raman spectra were recorded under potentiostatic conditions in the 1 M H2SO4 solution in the 800 - 1700 cm-1 range using 830 nm excitation laser and 1200 lines grating 25.
The Raman spectroelectrochemistry results of polyaniline electropolymerized on the electrografted gold substrate (PANi/amino/Au) are shown in the Figure 5. The signal assignment was based on the literature data11,26,27,28. At the starting potential of 0 mV, the bands at 1178 cm-1, 1265 cm-1 and 1608 cm-1 arising from the C-H in-plane bending, C-N stretching, and C-C stretching respectively, are observed and confirm that the polyaniline below the potential of A-redox couple exists in the leucoemeraldine form. The increase in the applied potential above the potential of the first redox couple (A) causes the formation of the C-N stretching bands at 1239 cm-1 and 1264 cm-1, and semiquinone polyaniline structure that is indicated by two overlapping peaks within the 1300-1420 cm-1 region. Further increase in the potential up to 500-700 mV, i.e. above the potential of the second redox couple (B), causes a correlated growth of three bands: at 1235 cm-1- C-N stretching, at 1483 cm-1- C=N stretching and at 1590 cm-1- C=C stretching, which are characteristic for the deprotonated quinoid ring. This is accompanied by the decrease in the relative intensity of the 1335 cm-1 band, indicating the transition of polyaniline into the pernigraniline form.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56653/56653fig1.jpg" /> 
Figure 1: Scheme of transmission IR-spectroelectrochemistry cell (a) and its side view after assembly (b). <a href="/files/ftp_upload/56653/56653fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56653/56653fig2.jpg" /> 
Figure 2: Schemes of reflectance cells for IR-spectroelectrochemistry. External reflectance cells a) and b) are used for the investigation of solute species. Internal reflectance cell c) is used for the investigation of species adsorbed on the electrode. <a href="/files/ftp_upload/56653/56653fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56653/56653fig3.jpg" /> 
Figure 3: Schemes of Raman spectroelectrochemical cell <a href="/files/ftp_upload/56653/56653fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56653/56653fig4v3.jpg" /> 
Figure 4: IR spectra of the monomer at various potentials applied <a href="/files/ftp_upload/56653/56653fig4v3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56653/56653fig5.jpg" /> 
Figure 5: Raman spectra of polyaniline at a different potential; insert: CV curve recorded for the polyaniline film <a href="/files/ftp_upload/56653/56653fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Raman and IR Spectroelectrochemical Methods as Tools to Analyze Conjugated Organic Compounds at JoVE.com

Raman and IR Spectroelectrochemical Methods as Tools to Analyze Conjugated Organic Compounds

A protocol of step-by-step Raman and IR spectroelectrochemical analysis is presented.

In the presented work, two spectroelectrochemical techniques are discussed as tools for the analysis of the structural changes occurring in the molecule ...

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Analysis of Volatile and Oxidation Sensitive Compounds Using a Cold Inlet System and Electron Impact Mass Spectrometry

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The analysis of volatile and oxidation sensitive compounds by mass spectrometry is not easily achieved, as all state-of-the-art mass spectrometric methods require at least one sample preparation step, e.g., dissolution and dilution of the analyte (electrospray ionization), co-crystallization of the analyte with a matrix compound (matrix-assisted laser desorption/ionization), or transfer of the prepared samples into the ionization source of the mass spectrometer, to be conducted under atmospheric conditions. Here, the use of a sample inlet system is described which enables the analysis of volatile metal organyls, silanes, and phosphanes using a sector field mass spectrometer equipped with an electron impact ionization source. All sample preparation steps and the sample introduction into the ion source of the mass spectrometer take place either under air-free conditions or under vacuum, enabling the analysis of compounds highly susceptible to oxidation. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes, which have to be handled using inert conditions, such as the Schlenk technique. The principle of operation is presented in this video.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes which have to be handled using inert conditions, such as the Schlenk technique.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The ...

Layer-by-layer Synthesis and Transfer of Freestanding Conjugated Microporous Polymer Nanomembranes

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in combination with their outstanding thermal and chemical stability, and low densities. However, their insoluble nature causes problems in their processing since usually applied techniques such as spin coating are not available. Especially for membrane applications, where the processing of CMP as thin films is desirable, the processing problems have hindered their commercial application.
Here we describe the interfacial synthesis of CMP thin films on functionalized substrates via molecular layer-by-layer (l-b-l) synthesis. This process allows the preparation of films with desired thickness and composition and even desired composition gradients.
The use of sacrificial supports allows the preparation of freestanding membranes by dissolution of the support after the synthesis. To handle such ultra-thin freestanding membranes the protection with sacrificial coatings showed great promise, to avoid rupture of the nanomembranes. To transfer the nanomembranes to the desired substrate, the coated membranes are upfloated at the air-liquid interface and then transferred via dip coating.

In this paper we describe the interfacial synthesis of conjugated microporous polymers (CMP) on sacrificial substrates, and the dissolution of the substrate for the preparation of freestanding CMP nanomembranes. In addition, we will describe how the fragile nanomembranes can be transferred to other substrates.

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in ...

Au-Interaction of Slp1 Polymers and Monolayer from Lysinibacillus sphaericus JG-B53 - QCM-D, ICP-MS and AFM as Tools for Biomolecule-metal Studies

In this publication the gold sorption behavior of surface layer (S-layer) proteins (Slp1) of Lysinibacillus sphaericus JG-B53 is described. These biomolecules arrange in paracrystalline two-dimensional arrays on surfaces, bind metals, and are thus interesting for several biotechnical applications, such as biosorptive materials for the removal or recovery of different elements from the environment and industrial processes. The deposition of Au(0) nanoparticles on S-layers, either by S-layer directed synthesis 1 or adsorption of nanoparticles, opens new possibilities for diverse sensory applications. Although numerous studies have described the biosorptive properties of S-layers 2-5, a deeper understanding of protein-protein and protein-metal interaction still remains challenging. In the following study, inductively coupled mass spectrometry (ICP-MS) was used for the detection of metal sorption by suspended S-layers. This was correlated to measurements of quartz crystal microbalance with dissipation monitoring (QCM-D), which allows the online detection of proteinaceous monolayer formation and metal deposition, and thus, a more detailed understanding on metal binding.
The ICP-MS results indicated that the binding of Au(III) to the suspended S-layer polymers is pH dependent. The maximum binding of Au(III) was obtained at pH 4.0. The QCM-D investigations enabled the detection of Au(III) sorption as well as the deposition of Au(0)-NPs in real-time during the in situ experiments. Further, this method allowed studying the influence of metal binding on the protein lattice stability of Slp1. Structural properties and protein layer stability could be visualized directly after QCM-D experiment using atomic force microscopy (AFM). In conclusion, the combination of these different methods provides a deeper understanding of metal binding by bacterial S-layer proteins in suspension or as monolayers on either bacterial cells or recrystallized surfaces.

Au-Interaction of Slp1 Polymers and Monolayer from Lysinibacillus sphaericus JG-B53 - QCM-D, ICP-MS and AFM as Tools for Biomolecule-metal Studies

To obtain basic information on the sorption and recycling of gold from aqueous systems the interaction of Au(III) and Au(0) nanoparticles on S-layer proteins were investigated. The sorption of protein polymers was investigated by ICP-MS and that of proteinaceous monolayers by QCM-D. Subsequent AFM enables the imaging of the nanostructures.

In this publication the gold sorption behavior of surface layer (S-layer) proteins (Slp1) of Lysinibacillus sphaericus JG-B53 is described. These ...

Preparation of Biopolymer Aerogels Using Green Solvents

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers (gelatin, agar, cellulose), only recently have biomasses been recognized as an abundant source of chemically diverse macromolecules for functional aerogel materials. Biopolymer aerogels (pectin, alginate, chitosan, cellulose, etc.) exhibit both specific inheritable functions of starting biopolymers and distinctive features of aerogels (80-99% porosity and specific surface up to 800 m2/g). This synergy of properties makes biopolymer aerogels promising candidates for a wide gamut of applications such as thermal insulation, tissue engineering and regenerative medicine, drug delivery systems, functional foods, catalysts, adsorbents and sensors. This work demonstrates the use of pressurized carbon dioxide (5 MPa) for the ionic cross linking of amidated pectin into hydrogels. Initially a biopolymer/salt dispersion is prepared in water. Under pressurized CO2 conditions, the pH of the biopolymer solution is lowered to 3 which releases the crosslinking cations from the salt to bind with the biopolymer yielding hydrogels. Solvent exchange to ethanol and further supercritical CO2 drying (10 - 12 MPa) yield aerogels. Obtained aerogels are ultra-porous with low density (as low as 0.02 g/cm3), high specific surface area (350 - 500 m2/g) and pore volume (3 - 7 cm3/g for pore sizes less than 150 nm).

A new way for the production of biopolymer-based aerogels by carbon dioxide (CO2) induced gelation is shown. The technique utilizes pressurized carbon dioxide (5 MPa) for the production of biopolymer hydrogels and supercritical CO2 (12 MPa) to convert gels into aerogels. The only solvents needed besides CO2 are water and ethanol.

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers ...

Fizzy Extraction of Volatile Organic Compounds Combined with Atmospheric Pressure Chemical Ionization Quadrupole Mass Spectrometry

Chemical analysis of volatile and semivolatile compounds dissolved in liquid samples can be challenging. The dissolved components need to be brought to the gas phase, and efficiently transferred to a detection system. Fizzy extraction takes advantage of the effervescence phenomenon. First, a carrier gas (here, carbon dioxide) is dissolved in the sample by applying overpressure and stirring the sample. Second, the sample chamber is decompressed abruptly. Decompression leads to the formation of numerous carrier gas bubbles in the sample liquid. These bubbles assist the release of the dissolved analyte species from the liquid to the gas phase. The released analytes are immediately transferred to the atmospheric pressure chemical ionization interface of a triple quadrupole mass spectrometer. The ionizable analyte species give rise to mass spectrometric signals in the time domain. Because the release of the analyte species occurs over short periods of time (a few seconds), the temporal signals have high amplitudes and high signal-to-noise ratios. The amplitudes and areas of the temporal peaks can then be correlated with concentrations of the analytes in the liquid samples subjected to fizzy extraction, which enables quantitative analysis. The advantages of fizzy extraction include: simplicity, speed, and limited use of chemicals (solvents).

Fizzy extraction is a new laboratory technique for analysis of volatile and semivolatile compounds. A carrier gas is dissolved in the liquid sample by applying overpressure and stirring the sample. The sample chamber is then decompressed. The analyte species are liberated to the gas phase due to effervescence.

Chemical analysis of volatile and semivolatile compounds dissolved in liquid samples can be challenging. The dissolved components need to be brought to ...

Grafting Multiwalled Carbon Nanotubes with Polystyrene to Enable Self-Assembly and Anisotropic Patchiness

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a free-radical polymerization strategy to enable the modulation of the nanotube surface properties and produce supramolecular self-assembly of the nanostructures. First, a selective hydroxylation of the pristine nanotubes through a biphasic catalytically mediated oxidation reaction creates superficially distributed reactive sites at the sidewalls. The latter reactive sites are subsequently modified with methacrylic moieties using a silylated methacrylic precursor to create polymerizable sites. Those polymerizable groups can address further polymerization of styrene to produce a hybrid nanomaterial containing PS chains grafted to the nanotube sidewalls. The polymer-graft content, amount of silylated methacrylic moieties introduced and hydroxylation modification of the nanotubes are identified and quantified by Thermogravimetric Analysis (TGA). The presence of reactive functional groups hydroxyl and silylated methacrylate are confirmed by Fourier Transform Infrared Spectroscopy (FT-IR). Polystyrene-grafted carbon nanotube solutions in tetrahydrofuran (THF) provide wall-to-wall collinearly self-assembled nanotubes when cast samples are analyzed by transmission electron microscopy (TEM). Those self-assemblies are not obtained when suitable blanks are similarly cast from analogous solutions containing non-grafted counterparts. Therefore, this method enables the modification of the nanotube anisotropic patchiness at the sidewalls which results into spontaneous auto-organization at the nanoscale.

A procedure for the synthesis of polystyrene-grafted multiwalled carbon nanotubes using successive chemical modification steps to selectively introduce the polymer chains to the sidewalls and their self-assembly via anisotropic patchiness is presented.

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a ...

Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera

Here, we present a sensible method of the acquisition and analysis of time-resolved photoluminescence using an ultrafast iCCD camera. This system enables the acquisition of photoluminescence spectra covering the time regime from nanoseconds up to 0.1 s. This enables us to follow the changes in the intensity (decay) and emission of the spectra over time. Using this method, it is possible to study diverse photophysical phenomena, such as the emission of phosphorescence, and the contributions of prompt and delayed fluorescence in molecules showing thermally activated delayed fluorescence (TADF). Remarkably, all spectra and decays are obtained in a single experiment. This can be done for solids (thin film, powder, crystal) and liquid samples, where the only limitations are the spectral sensitivity of the camera and the excitation wavelength (532 nm, 355 nm, 337 nm, and 266 nm). This technique is, thus, very important when investigating the excited state dynamics in organic emitters for their application in organic light-emitting diodes and other areas where triplet harvesting is of paramount importance. Since triplet states are strongly quenched by oxygen, emitters with efficient TADF luminescence, or those showing room temperature phosphorescence (RTP), must be correctly prepared in order to remove any dissolved oxygen from solutions and films. Otherwise, no long-lived emission will be observed. The method of degassing solid samples as presented in this work is basic and simple, but the degassing of liquid samples creates additional difficulties and is particularly interesting. A method of minimizing solvent loss and changing the sample concentration, while still enabling to remove oxygen in a very efficient and a repeatable manner, is presented in this work.

Here, we present a method of the spectroscopic characterization of organic molecules by means of time-resolved photoluminescence spectroscopy on the nanosecond-to-millisecond timescale in oxygen-free conditions. Methods to efficiently remove oxygen from the samples and, thus, limit luminescence quenching are also described.

Here, we present a sensible method of the acquisition and analysis of time-resolved photoluminescence using an ultrafast iCCD camera. This system enables ...

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, allowing for the synthesis of isotactic poly(&#945;-hydroxy acids) with expected molecular weights (&#62;140 kDa) and narrow molecular weight distributions (Mw/Mn &#60; 1.1). This ring-opening polymerization is mediated by Ni and Zn complexes in the presence of an alcohol initiator and a photoredox Ir catalyst, irradiated by a blue LED (400 - 500 nm). The polymerization is performed at a low temperature (-15 &#176;C) to avoid undesired side reactions. The complete monomer consumption can be achieved within 4 - 8 hours, providing a polymer close to the expected molecular weight with narrow molecular weight distribution. The resulted number-average molecular weight shows a linear correlation with the degree of polymerization up to 1000. The homodecoupling 1H NMR study confirms that the obtained polymer is isotactic without epimerization. This polymerization reported herein offers a strategy for achieving rapid, controlled O-carboxyanhydrides polymerization to prepare stereoregular poly(&#945;-hydroxy acids) and its copolymers bearing various functional side-chain groups.

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

A protocol for the controlled photoredox ring-opening polymerization of O-carboxyanhydrides mediated by Ni/Zn complexes is presented.

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, ...

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

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance (EPR) or ultraviolet-visible and near-infrared (UV-Vis-NIR) spectroscopies, we obtain useful information such as electron affinity, ionization potential, band-gap energies, the type of charge carriers, and degradation information that can be used to synthesize stable organic electronic devices. In this study, we present electrochemical and spectroelectrochemical methods to analyze the processes occurring in active layers of an organic device as well as the generated charge carriers.

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.

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance ...

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &#960;-conjugate Systems

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near infrared (near-IR) transitions, because it can overcome the low sensitivity of spontaneous Raman spectrometers in the near-IR region. Here, we describe technical details of a femtosecond time-resolved near-IR multiplex stimulated Raman spectrometer that we have recently developed. A description of signal generation and optimization, measurement, data acquisition, and calibration and correction of recorded data is provided as well. We present an application of our spectrometer to analyze the excited-state dynamics of &#946;-carotene in toluene solution. A C=C stretch band of &#946;-carotene in the second lowest excited singlet (S2) state and the lowest excited singlet (S1) state is clearly observed in the recorded time-resolved stimulated Raman spectra. The femtosecond time-resolved near-IR stimulated Raman spectrometer is applicable to the structural dynamics of &#960;-conjugate systems from simple molecules to complex materials.

Ultrafast Time-resolved Near-IR Stimulated Raman Measurements of Functional &amp;#960;-conjugate Systems

Details of signal generation and optimization, measurement, data acquisition, and data handling for a femtosecond time-resolved near-IR stimulated Raman spectrometer are described. A near infrared stimulated Raman study on the excited-state dynamics of &#946;-carotene in toluene is shown as a representative application.

Femtosecond time-resolved stimulated Raman spectroscopy is a promising method of observing the structural dynamics of short-lived transients with near ...