Sensitizers light absorption

Figure 3. Photocatalytic cycles based on an oxidative (left) and reductive (right) quenching of an excited polypyridine complex M. (The photosensitizer M in these cycles has been called light absorption sensitizer (LAS), since it enables a photochemical reactions between chemical species which do not absorb light [74, 266].)...

Studies in these fields [16] have shown that transition metal complexes may play the role of sensitizers both in the photoinduced processes schematized by Eq. 15 and in the light generating processes schematized by Eq. (16). In the first case, the complex can be called a light absorption sensitizer (LAS), while in the second case it can be called a light emission sensitizer (LES). High luminescence efficiency is a useful property for a LAS, and a necessary requirement for a LES. 

The task of the mediator is to absorb light and to make light energy available as chemical energy for the electron transfer process. Such mediators are usually called photosensitizers. We prefer to call them light absorption sensitizers (LAS) [36] to underline their role and to use a parallel expression in the case of the mediators of chemiluminescent electron transfer processes (vide infra). 

Fig.15 Light driven electron transfer process via the intermediacy of a light absorption sensitizer (LAS).

To determine of Ce(IV) in acid soluble single crystals, a simple and sensitive method is proposed. The method is based on the reaction of tropeoline 00 oxidation by cerium(IV) in sulfuric acid solution with subsequent measurement of the light absorption decrease of the solution. The influence of the reagent concentration on the analysis precision is studied. The procedure for Ce(IV) determination in ammonium dihydrophosphate doped by cerium is elaborated. The minimal determined concentration of cerium equal to 0.04 p.g/ml is lower than that of analogous methods by a factor of several dozens. The relative standard deviation does not exceed 0.1. 

Balzani, V., Barigelletti, F., De Cola, L. Metal Complexes as Light Absorption and Light Emission Sensitizers. 158, 31-71 (1990). 

Figure 11 Illustration of the interfacial CT processes in a nanocrystalline dye-sensitized solar cell. S / S+/S represent the sensitizer in the ground, oxidized and excited state, respectively. Visible light absorption by the sensitizer (1) leads to an excited state, followed by electron injection (2) onto the conduction band of Ti02. The oxidized sensitizer (3) is reduced by the I-/I3 redox couple (4) The injected electrons into the conduction band may react either with the oxidized redox couple (5) or with an oxidized dye molecule (6).

In principle, EPR spectrometry is well suited as a method to monitor kinetic events however, in practice, the time required to tune the spectrometer, and its intrinsically low sensitivity compared to fluorescence or light-absorption spectrometry, affect its competitiveness. Relatively slow reactions on the timescale of minutes, such as the decomposition of the DMPO-superoxide adduct and the subsequent formation of the hydroxyl radical adduct (cf. Pou et al. 1989) are readily followed, either as the first-order disappearance of the DMPO/ OOH signal... 

Detection of the presence of certain analytes in the fluid can also be accomplished if the analytes have light absorption in the wavelength range of interest. The sensitivity can be enhanced by using the microresonator structure due to the increased... 

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