Bleaching behavior

Pettinger, B., Ren, B., Picardi, G., Schuster, R. and Ertl, G. (2005) Tip-Enhanced Raman spectroscopy (TERS) of malachite green isothiocyanate at Au(lll) bleaching behavior under the influence of high electromagnetic flelds./. Raman Spectrosc., 36, 541-550. 

In September 2000, Hayazawa and coworkers reported the next study on apertureless SNOM using a silver-coated cantilever and a dye-coated silver film on a glass slide [137]. The dye was rhodamine 6g (Rh-6g). A 40-fold enhancement of Raman scattering was observed with a 4 8-nm laser excitation an enhancement of fluorescence was also noticed (see Fig. 10.16) [137]. The authors observed bleaching behavior for rhodamine 6g, but did not mention whether or not the bleaching rate was tip-enhanced. Instead, they pretreated this system with 20-min illumination until a stationary state was reached. 

Compounds lb and 2b were the Urst fluorinated ligands tested in Mn-catalyzed alkene epoxidation [5,6]. The biphasic Uquid system perfluorooc-tane/dichloromethane led to excellent activity and enantioselectivity (90% ee) in the epoxidation of indene with oxygen and pivalaldehyde (Scheme 1, Table 1). In addition, the fluorous solution of the catalyst was reused once and showed the same activity and selectivity. This represents a considerable improvement over the behavior in the homogeneous phase, where the used catalyst was bleached and reuse was impossible. Unfortunately, indene was the only suitable substrate for this system, which failed to epoxidize other alkenes (such as styrene or 1,2-dihydronaphthalene) with high enantioselectivity. The system was also strongly dependent on the oxidant and only 71% ee was obtained in the epoxidation of indene with mCPBA at - 50 °C. 

The knowledge that allows chemists to describe, interpret, and predict the behavior of chemical substances is gained by making careful experimental measurements. The properties of a sample can be divided into physical properties, which can be measured without observing a chemical reaction, and chemical properties, which are displayed only during a chemical transformation. Physical properties include familiar attributes such as size, color, and mass. Some chemical properties also are familiar to us. As examples, bleach reacts chemically with many colored substances to destroy their colors, and molecular oxygen reacts chemically with many fuels to generate heat. 

Fe (CN)jX species, pulse-irradiated at 530 nm, display bleaching within the 20 ns pulse. After bleaching, the original absorbance is redeveloped at rates linearly depending on the concentration of free X in solution. For 1 (but not 2) a second small absorbance change ( = 10%) accompanied the first. Explain this behavior. 

The submitters have carried out runs using up to 4 1. of the commercial bleach solution (3 moles)—as the largest scale conveniently run in the laboratory—and found no change in the reaction behavior. 

Schneider et al. [63] investigated the photochemistry of the spiro-oxazine merocyanines pumping and probing at 570 nm in acetonitrile. The found that the solution bleached within the <5-psec pulse duration. The bleached state recovered with at least a biexponential behavior, and from their fluorescence decay measurements, three exponentials were required to fit the decay. They attribute these findings to the possibility of three merocyanine isomers that are in equilibrium. Their compounds feature geminal ethyl groups on the indoline moieties and this may influence the system as compared to NOSIl. 

Electrochromic materials of interest can be classified according to three types of color change (1) from a bleached state (transparent) to a colored state, (2) between two colored states, and (3) between several colored states, if more than two redox states are accessible. This behavior is called polyelectrochromic... 

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