UV- and visible light absorption

Internal absorpsion loss UV and visible light absorption by electron transition ( a. ) infrared absorption by vibronic transition ( a )... 

Ultraviolet (UV) and visible light absorption 0.2 < X(p.m) < 0.8 Functional group analysis Pyrolysis/ozonolysis... 

Cabot has recently introduced a new carbon black called Elftex PI00, for use in pipe. It is said to be superior in dispersibility, particle size, moisture absorption and purity. (Moisture absorption in carbon black can cause processing problems and surface defects.) Elftex PI00 also has good UV and visible light absorption. 

A typical photochemical isomerization of the azobenzene amphiphile was found in an ethanol solution. A trans isomer converted to a cis isomer with ultraviolet irradiation. Back reaction from cis to trans was accelerated when a weak n-n absorption band of the cis isomer at ca.450nm was excited (Figure 21a). An alternative irradiation of uv and visible light to the ethanol solution gave reversible changes of the ji-ji transition between 355nm and 325nm attributed to the trans and cis isomers, respectively. 

We have now looked at the way photons are absorbed. Photons of UV and visible light cause electrons to promote between orbitals. Infrared photons have less energy, and are incapable of exciting electrons between orbitals, but they do allow excitation between quantized vibrational levels. The absorption of microwaves, which are less energetic still, effects the excitation between quantized rotational levels. 

When a photon passes close to a molecule, there is an interaction between the electromagnetic field associated with the molecule and that associated with the radiation. If, and only if, the radiation is absorbed by the molecule as a result of this interaction, can the radiation be effective in producing photochemical changes (Grotthus-Draper law, see, e.g., Finlay son-Pitts and Pitts, 1986). Therefore, the first thing we need to be concerned about is the probability with which a given compound absorbs uv and visible light. This information is contained in the compounds uv/vis absorption spectrum, which is often readily available or can be easily measured with a spectrophotometer. 

Improvement of the efficiency for the photochemical splitting of water was the aim of Morris and Mallouk [83], A parallel optical screening method was developed to select photocatalytically active catalysts by their absorption spectra with UV and visible light. 

In solution, 10a showed typical photochromic behavior on irradiation with UV and visible light (Fig. 9.4). Although the radical moiety has a weak absorption in the region from 550 to 700 nm, this did not prevent the photochromic reaction. Almost 100 % photochemical conversions were observed in both the cyclization from the open-ring isomer 10a to the closed-ring isomer 10b and the cycloreversion from 10b to 10a. For the practical use of photochromic devices, high conversion is one of the most important characteristics. 

Diarylethenes 16 and 17 underwent reversible photochromic reactions by alternate irradiation with UV and visible light. A typical absorption spectral change for 16 is shown in Fig. 9.6. The changes in the ESR spectra accompanying the photo-chromic reaction were examined for diarylethenes 16 and 17. Figure 9.7 shows the ESR spectra at different stages of the photochromic reaction of 16a. The ESR spectrum of 16a showed 15 complex lines. This suggests that the two... 

Compound 24(00) underwent photochromic reaction by alternate irradiation with UV and visible light. Upon irradiation of the ethyl acetate solution of 24(00) with 313-nm light, an absorption at 560 nm appeared, as shown in Fig. 9.10. This absorption grew and shifted and the system reached the photostation-ary state after 120 min. The color of the solution changed from pale blue to red-purple and then to blue-purple. Such a red spectral shift suggests the formation of 24(CC). The isosbestic point was maintained at an initial stage of irradiation,... 

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. 

Atoms of certain metals will absorb and emit radiation of specific wavelengths when heated in a flame, in direct proportion to the number of atoms present. Atomic spectrophotometric techniques measure the absorption or emission of particular wavelengths of UV and visible light, to identify and quantify such metals. 

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