Electrochemical resonance Raman sensitivity enhancement

Rather serendipitously, transition metal macrocycles display electronic transitions in the U Vand visible spectral regions with very large cross sections. These conditions do not only lead to increased sensitivity in reflectance measurements in this energy range, but also contribute to enhance Raman signals through electronic resonances. This sub-section addresses salient aspects of in situ spectroscopy as applied to the study of macrocydic modified surfaces of relevance to the electrochemical reduction of dioxygen. 

In this chapter, electrochemical properties of ET proteins at electrode interfaces studied by spectroelectrochem-ical techniques are described. In situ spectroelectrochemical techniques at well-defined electrode surfaces are sufficiently selective and sensitive to distinguish not only steady state structures and oxidation states of adsorbed species but also dynamics of reactants, products, and intermediates at electrode surfaces on a monolayer level. The spectroelectrochemical techniques used in studies of ET proteins include IR reflection-absorption, potential-modulated UV-vis reflectance (electroreflectance), surface-enhanced Raman scattering (SERS) and surface plasmon resonance, total internal reflection fluorescence, (TIRE) and absorbance linear dichroism spectroscopies. 

One of the most important tasks of modern electrochemistry is to develop microscopic pictures of solid-liquid interfaces and thus to provide a basis for the detailed understanding of electrochemical processes. To fulfill this task, the development of surface-specific and structure-sensitive in-situ methods to characterize electrochemical interfacial processes is indispensable. As early as 1970, Professor Martin Fleischmann was one of the pioneers in exploring in-situ methods that included surface-enhanced Raman spectroscopy [1], surface X-ray diffraction [2] and nuclear magnetic resonance [3] to characterize electrochemical interfaces. Nowadays, nontraditional electrochemical methods that include spectroscopic and microscopic as well as diffraction techniques have been extensively applied, and this has promoted an understanding of electrochemical interfaces at both atomic and molecular levels. 

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