Visible absorption peak

A UV or visible absorption peak is caused by the promotion of an electron in one orbital (usually a ground-state orbital) to a higher orbital. Normally the amount of energy necessary to make this transition depends mostly on the nature of the two orbitals involved and much less on the rest of the molecule. Therefore, a simple... 

A sensitive spectrophotometric method based on the strong absorption of the aminochrome-sodium bisulfite addition products (see Section IV, F) at ca. 350 m/x. has been described recently by van Espen128and Oesterling and Tse 277-278 for determining total catecholamines. While not as sensitive as the fluorimetric procedures, this method is considerably more sensitive than the older colorimetric methods based on the visible absorption peak of the aminochromes. Also, it does not have many of the disadvantages (e.g. costly equipment and unstable blanks) often associated with fluorimetric techniques. The basic procedure can be satisfactorily applied to the differential determination of mixtures of adrenaline, noradrenaline, dopamine, metanephrine, and normetanephrine.178... 

Where visible absorption peaks have been found in natural photoreceptor material, no NMR or X-ray crystallographic data has been put forward to demonstrate the presence of a retinene in the material (See Chapter 7). It is proposed here that any such tests will demonstrate the presence of a Rhodonine instead. Rhodonine contains two polar groups separated by a conjugated carbon chain. It is further proposed that opsin is only present as a completely passive substrate. Its association with the liquid crystalline Rhodonine is via a weak hydrogen bond that does not change the electronic configuration of the Rhodonines. 

Electronic excitation in molecules is accompanied by changes in vibrational or rotational energy levels. The energy levels for these excitations are considerably smaller than the energy differences between electronic excitations. These transitions are superposed on the electronic excitations, which results in a large number of absorption peaks so closely spaced that the spectrophotometer cannot resolve them. For this reason, UV-visible absorption peaks usually are much broader than IR absorption peaks. 

The visible absorption peak of 7-methyladrenochrome (63) is observed at 534 nm [146], compared with a normal range of 470 to 495 nm [29]. This bathochromic shift due to the 7-methyl substituent appears to be general, since solutions of 7-methyldopachrome (64) and 4,7-dimethyldopachrome (65) were described as being deep violet in colour [147]. The actual spectra of these compounds were not, however, reported. 

Many organic compounds such as lycopene are colored because their HOMO-LUMO energy gap is small enough that appears m the visible range of the spec trum All that is required for a compound to be colored however is that it possess some absorption m the visible range It often happens that a compound will have its k m the UV region but that the peak is broad and extends into the visible Absorption of the blue to violet components of visible light occurs and the compound appears yellow... 

Both HMR and MR have strong absorption peaks in the visible portion of the spectrum the colour change interval from pH 4 to pH 6 can be conveniently obtained with a sodium acetate-acetic acid buffer system. 

The conformational mobility of a chromophoric main-chain polymer is often connected to its electronic structure. Therefore, changes in the UV-visible absorption spectra and/or chiroptical properties are spectroscopically observable as thermo-, solvato-, piezo-, or electrochromisms. It is widely reported that o-conjugating polysilanes exhibit these phenomena remarkably clearly.34 However, their structural origins were controversial until recently, since limited information was available on the correlation between the conformational properties of the main chain, electronic state, and (chir)optical characteristics. In 1996, we reported that in various polysilanes in tetrahydrofuran (THF) at 30°C, the main-chain peak intensity per silicon repeat unit, e (Si repeat unit)-1 dm3 cm-1, increases exponentially as the viscosity index, a, increases.41 Although conventional viscometric measurements often requires a wide range of low-dispersity molecular-weight polymer samples, a size exclusion chromatography (SEC) machine equipped with a viscometric detector can afford... 

In Fig. 15 are shown UV-visible absorption spectra of type a and type b of 15 bilayers consisting of an alternate A-S-D triad-CaT (1 5) and a pure CaT mono-layer and type a of 15 bilayers containing A-S dyads in place of the triads. Hie LB films of type a were deposited on quartz plates, but the LB film of type b on a chemically modified quartz plate by octadecyltrichlorosilane. An absorption peak around 450 nm can be assigned to the acylated perylene moieties for the dyad and... 

Figure 1.14 Raman spectra from a 0.1 wt% Mo03/y-AI203 catalyst obtained by using different (488, 325, and 244 nm) laser excitation energies [108], The UV-Vis absorbance spectrum is reported in the inset to indicate that while the catalyst does not absorb light in the visible region, it does show two UV absorption peaks at 290 and 220 nm. The data clearly illustrate the advantage of using ultraviolet (244 nm) light for Raman excitation, since the spectrum obtained with visible (488 nm) radiation is dominated by the fluorescence of the solid. (Reproduced with permission from Elsevier.)...

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