Spectroelectrochemistry absorption spectroscopy

Optical Spectroscopy General principles and overview, 246, 13 absorption and circular dichroism spectroscopy of nucleic acid duplexes and triplexes, 246, 19 circular dichroism, 246, 34 bioinorganic spectroscopy, 246, 71 magnetic circular dichroism, 246, 110 low-temperature spectroscopy, 246, 131 rapid-scanning ultraviolet/visible spectroscopy applied in stopped-flow studies, 246, 168 transient absorption spectroscopy in the study of processes and dynamics in biology, 246, 201 hole burning spectroscopy and physics of proteins, 246, 226 ultraviolet/visible spectroelectrochemistry of redox proteins, 246, 701 diode array detection in liquid chromatography, 246, 749. 

Electronic Absorption Spectroelectrochemistry. Electronic absorption spectroscopy with UV and visible light is a form of spectroelectrochemistry typically employed as a transmission experiment to investigate changes in absorbance due to a species being oxidized or reduced. Typically the potential is scanned while the absorbance at a particular wavelength is recorded or the potential is stepped while a full spectrum is collected. Spectroelectrochemistry of this type can be used to establish spectroscopic signatures of reduced or oxidized forms of a compound that can be correlated to excited state transient absorbance spectroscopy. 

Electronic coupling can be probed using electrochemistry. Brewer and Richter investigated bimetallic complexes of the form [(bpy)20s(BL)0s(bpy)2] " (BE = 2,3-bis(2-pyridyl)pyrazine (dpp), 2,3-bis(2-pyridyl)quinoxaline (dpq) or 2,3-bis(2-pyridyl)benzoquinoxaline (dpb), and bpy = 2,2 -bipyridine) by electronic absorption spectroscopy and spectroelectrochemistry. When BE = dpb, the 1/2... 

Instrumentation. In order to employ local enhancement of infrared absorption by surface plasmon polaritons that cause locally enhanced surface electromagnetic fields, a suitable optical arrangement is needed [295]. Surface enhanced infrared absorption spectroscopy can also be observed in the transmission mode [285, 296]. However, since no application of this approach in spectroelectrochemistry has been reported so far, it is not discussed further. 

Cappel UB, Gibson EA, Hagfeldt A, Boschloo G (2009) Dye regeneration by spiro-MeOTAD in solid state dye-sensitized solar cells studied by photoinduced absorption spectroscopy and spectroelectrochemistry. J Phys Chem C 113 6275-6281... 

See also Colorimetry, Theory Dyes and Indicators, Use of UV-Visible Absorption Spectroscopy Ellipsometry Light Sources and Optics Spectroelectrochemistry, Applications. 

Infrared spectroelectrochemical methods, particularly those based on Fourier transform infrared (FTIR) spectroscopy can provide structural information that UV-visible absorbance techniques do not. FTIR spectroelectrochemistry has thus been fruitful in the characterization of reactions occurring on electrode surfaces. The technique requires very thin cells to overcome solvent absorption problems. 

Spectroelectrochemistry, reflection mode — The interaction of electromagnetic radiation with matter (-> spectroscopy) may occur by absorption or scattering when radiation impinges on matter or passes through matter. In the latter case (transmission mode) the radiation before and after passage is evaluated in order to obtain the desired spectrum. In studies of opaque materials or of surfaces interacting with matter inside the (bulk)... 

For the first reduction the IR shifts point to a porphyrin-centred electron transfer. This is supported by further spectroscopy on the anion radical complexes [(Por)Ru(CO)(L)]. The observed EPR lines are narrow, unstructured, with g values around 2. The UV-Vis-NIR spectra of the radical anions are characterised by redshifted Soret bands of reduced intensity, a weak structured band system around 600 nm and weak broad absorptions around 800 or 900 nm (see Figure 4.15). Further support comes from resonance Raman investigations on [(OEP)Ru(CO)(THF)] for which the observed Raman bands fit perfectly to those of the [(OEP)VO] radical anion. There is some evidence that if the spectroelectrochemistry is not carried out in very aprotic and unpolar solvents or traces of water are present, the radical anionic complexes are readily transformed. This has been investigated for the [(OEP)Ru(CO)(L)] system, where the use of solvents like MeOH or nitriles for the electrochemical reduction leads to altered species with unreduced porphyrin ligands (see Figure 4.15)." ... 

Regarding surface spectroelectrochemistry, the intense interest in the electrochemistry of single crystal surfaces, adatoms, oxide layers, and monolayers in the last decade has seen not only the enhancement of traditional methods (e.g., infrared (IR) and Raman microspectroscopy) but also the development of relatively new surface specific methods such as second-harmonic generation, sum-frequency generation, surface plasmon resonance (SPR), and surface-enhanced resonance spectroscopy (SERS). The increased access to synchrotron radiation has led to X-ray absorption and X-ray diffraction methods becoming more feasible as in situ techniques for thin films or species generated close to the electrode. In this article, for... 

ESR spectroscopy directly proves the magnetic nature of charged conjugated molecules. Thus, combining in situ Vis-NIR and ESR spectroelectrochemistry gives a deep insight into the nature of the doped states. Indeed, this rather sophisticated technique was crucial for the assignment of the electronic absorption bands mentioned above [i25, 126]. 

Figure 9.9 In Situ Vis-NIR absorption spectra recorded upon doping of poly(3-decylthiophene). Reprinted with permission from /. Pron, P. Rannou, M. Zagorska, Spectroscopy and spectroelectrochemistry of polyanilines and polythiophenes, in Electronic and Optical Properties of Conjugated Systems in Condensed Phases, Research Signpost, Trivandrum, 2003. Copyright (2003) Research Signpost...

Of particular importance in this context are comparative investigations performed under clean room or even ultrahigh-vacuum conditions on the one side (characterization of "model systems") and under controlled atmospheric pressure or electrochemical conditions on the other side (characterization of "real systems") If at all possible, in-situ techniques should be applied which monitor structures under both, ideal conditions as well as under those natural environment conditions in which the final device is used These include in particular various optical techniques such as absorption and reflection spectroscopy between the IR and UV range, measurements of dichroic ratios, Raman spectroscopy, surface plasmon resonance spectroscopy, spectroelectrochemistry, or SXM-techniques [12]... 

Spectroelectrochemistry encompasses a group of techniques that allow simultaneous acquisition of electrochemical and spectroscopic information in situ in an electrochemical cell. A wide range of spectroscopic techniques may be combined with electrochemistry, including electronic (UV-visible) absorption and reflectance spectroscopy, luminescence spectroscopy, infrared and Raman spectroscopies, electron spin resonance spectroscopy and ellipsometry. Molecular properties such as molar absorption coefficients, vibrational absorption frequencies and electronic or magnetic resonance frequencies, in addition to electrical parameters such as current, voltage or charge, are now being used routinely for the study of electron transfer reaction pathways and the fundamental molecular states at interfaces. In this article the principles and practice of electronic spectroelectrochemistry are introduced. 

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