Polarized resonance Raman dispersion spectroscopy on metalporphyrins

2001 ◽  
Vol 05 (03) ◽  
pp. 198-224 ◽  
Author(s):  
REINHARD SCHWEITZER-STENNER
Keyword(s):  
Resonance Raman Spectroscopy ◽  
Resonance Raman ◽  
Resonance Excitation ◽  
Depolarization Ratio ◽  
Prosthetic Group ◽  
Excitation Energies ◽  
Absorption Bands ◽  
Porphyrin Macrocycle ◽  
Ideal Tool ◽  
The Relationship

Resonance Raman spectroscopy is an ideal tool to investigate the structural properties of chromophores embedded in complex (biological) environments. This holds particularly for metalporphyrins which serve as prosthetic group in various proteins. Resonance Raman dispersion spectroscopy involves the measurement of resonance excitation and depolarization ratios of a large number of Raman lines at various excitation energies covering the spectral region of the chromophore's optical absorption bands. Thus, one obtains resonance excitation profiles and the depolarization ratio dispersion of these bands. While the former contains information about the structure of excited electronic states involved in the Raman scattering process, the latter reflects asymmetric perturbations which lower the porphyrin macrocycle symmetry from ideal D4h. The article introduces and compares different quantum mechanical approaches designed to quantitatively analyze both resonance excitation and the relationship between symmetry lowering and depolarization ratio dispersion.

Application of UV-Vis and resonance Raman spectroscopy to study bleaching and photoyellowing of thermomechanical pulps

Holzforschung ◽  
2006 ◽  
Vol 60 (3) ◽  
pp. 231-238 ◽  
Author(s):  
Anna-Stiina Jääskeläinen ◽  
Anna-Maija Saariaho ◽  
Jouko Vyörykkä ◽  
Tapani Vuorinen ◽  
Pavel Matousek ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Light Exposure ◽  
Resonance Raman Spectroscopy ◽  
Resonance Raman ◽  
Excitation Wavelength ◽  
Thermomechanical Pulp ◽  
Pulp Bleaching ◽  
Absorption Bands ◽  
Peroxide Bleaching ◽  
Brightness Reversion

Abstract The chemistry of thermomechanical pulp bleaching and brightness reversion was studied. First, UV-Vis reflectance spectroscopy was used to obtain information on the reactive structures in pulp. Based on these data, a Raman excitation wavelength was chosen close to the absorption bands of the chromophores formed to take advantage of the resonance enhancement (resonance Raman spectroscopy). Fluorescence was rejected with a picosecond Kerr gate. The results revealed that coniferyl aldehyde structures were partly removed by alkaline peroxide bleaching and these structures were further degraded during light exposure. However, this reaction was obviously not responsible for chromophore formation in the pulp. On the other hand, based on the resonance Raman spectra, formation of quinonoid structures, possibly para-quinones, was a more prominent explanation for the brightness reversion.

scholarly journals Resonance Raman Spectro-Electrochemistry to Illuminate Photo-Induced Molecular Reaction Pathways

Molecules ◽  
2019 ◽  
Vol 24 (2) ◽  
pp. 245 ◽  
Author(s):  
Linda Zedler ◽  
Sven Krieck ◽  
Stephan Kupfer ◽  
Benjamin Dietzek
Keyword(s):  
Structural Changes ◽  
Raman Band ◽  
Resonance Raman Spectroscopy ◽  
Spectroscopic Method ◽  
Resonance Raman ◽  
Reaction Pathways ◽  
Excitation Wavelength ◽  
Absorption Bands ◽  
The Individual ◽  
Sequential Reduction

Electron transfer reactions play a key role for artificial solar energy conversion, however, the underlying reaction mechanisms and the interplay with the molecular structure are still poorly understood due to the complexity of the reaction pathways and ultrafast timescales. In order to investigate such light-induced reaction pathways, a new spectroscopic tool has been applied, which combines UV-vis and resonance Raman spectroscopy at multiple excitation wavelengths with electrochemistry in a thin-layer electrochemical cell to study [RuII(tbtpy)2]2+ (tbtpy = tri-tert-butyl-2,2′:6′,2′′-terpyridine) as a model compound for the photo-activated electron donor in structurally related molecular and supramolecular assemblies. The new spectroscopic method substantiates previous suggestions regarding the reduction mechanism of this complex by localizing photo-electrons and identifying structural changes of metastable intermediates along the reaction cascade. This has been realized by monitoring selective enhancement of Raman-active vibrations associated with structural changes upon electronic absorption when tuning the excitation wavelength into new UV-vis absorption bands of intermediate structures. Additional interpretation of shifts in Raman band positions upon reduction with the help of quantum chemical calculations provides a consistent picture of the sequential reduction of the individual terpyridine ligands, i.e., the first reduction results in the monocation [(tbtpy)Ru(tbtpy•)]+, while the second reduction generates [(tbtpy•)Ru(tbtpy•)]0 of triplet multiplicity. Therefore, the combination of this versatile spectro-electrochemical tool allows us to deepen the fundamental understanding of light-induced charge transfer processes in more relevant and complex systems.

scholarly journals Structure of the retinal chromophore in sensory rhodopsin I from resonance Raman spectroscopy

1989 ◽  
Vol 264 (31) ◽  
pp. 18280-18283
Author(s):  
S P Fodor ◽  
R Gebhard ◽  
J Lugtenburg ◽  
R A Bogomolni ◽  
R A Mathies
Keyword(s):  
Raman Spectroscopy ◽  
Resonance Raman Spectroscopy ◽  
Resonance Raman ◽  
Sensory Rhodopsin ◽  
Retinal Chromophore ◽  
Sensory Rhodopsin I
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