UV-vis absorption band

Comparing the IR spectrum in Figure 10.15 to the UV/Vis spectrum in Figure 10.17, we note that UV/Vis absorption bands are often significantly broader than those for IR absorption. Figure 10.14 shows why this is true. When a species... 

Quantitative Analysis of Mixtures The analysis of two or more components in the same sample is straightforward if there are regions in the sample s spectrum in which each component is the only absorbing species. In this case each component can be analyzed as if it were the only species in solution. Unfortunately, UV/Vis absorption bands are so broad that it frequently is impossible to find appropriate wavelengths at which each component of a mixture absorbs separately. Earlier we learned that Beer s law is additive (equation 10.6) thus, for a two-component mixture of X and Y, the mixture s absorbance, A, is... 

To substitute the strongly bound axial CO ligand of the ruthenium or osmium center, it is necessary to employ more drastic conditions than simple stirring at room temperature. Imamura (11,20) used photolysis to synthesize porphyrin trimers on the basis of simultaneous coordination of two 4-pyridyl porphyrins to the same ruthenium porphyrin (12, Fig. 3). Some interesting photophysical behavior was observed for these systems. The trimers have an extra UV-Vis absorption band at about 450 nm which is ascribed to metal-ligand charge transfer (MLCT), a d7r(Ru(II))-7r (OEP) transition. This band shows a batho-chromic shift in more polar solvents, and decreased in intensity when... 

PPS was discussed in terms of a network structure, and showed a broad UV-VIS absorption band extending to 420 nm, while PMPS with a linear Si skeleton showed by comparison, a relatively sharp o-a absorption band at 334 nm, as shown in Figure 55(a). The emission spectra were also very different, as is evident in Figure 55(b). 

A series of novel ruthenium(IV) dioxolene complexes, formally [3 + 2] cycloadducts, have been obtained via the reaction of cix-[Ru (0)2(Me3tacn)(CF3C02)] with trimethylsilylacetylenes (Scheme 14). " These dark blue complexes display a characteristic UV-vis absorption band at 550-680 nm. They are also characterized by electrospray mass spectrometry. The X-ray structure of the complex formed with bis(trimethylsilyl)acetylene has been determined the two Ru—O bonds of the metallocycle are of the same length (1.978 A). 

Another transient aminoxyl radical has been generated , and employed in H-abstraction reactivity determinations" . Precursor 1-hydroxybenzotriazole (HBT, Table 2) has been oxidized by cyclic voltammetry (CV) to the corresponding >N—O species, dubbed BTNO (Scheme 9). A redox potential comparable to that of the HPI —PINO oxidation, i.e. E° 1.08 V/NHE, has been obtained in 0.01 M sodium acetate buffered solution at pH 4.7, containing 4% MeCN". Oxidation of HBT by either Pb(OAc)4 in AcOH, or cerium(IV) ammonium nitrate (CAN E° 1.35 V/NHE) in MeCN, has been monitored by spectrophotometry , providing a broad UV-Vis absorption band with A-max at 474 nm and e = 1840 M cm. As in the case of PINO from HPI, the absorption spectrum of aminoxyl radical BTNO is not stable, but decays faster (half-life of 110 s at [HBT] = 0.5 mM) than that of PINO . An EPR spectrum consistent with the structure of BTNO was obtained from equimolar amounts of CAN and HBT in MeCN solution . Finally, laser flash photolysis (LFP) of an Ar-saturated MeCN solution of dicumyl peroxide and HBT at 355 nm gave rise to a species whose absorption spectrum, recorded 1.4 ms after the laser pulse, had the same absorption maximum (ca 474 nm) of the spectrum recorded by conventional spectrophotometry (Scheme 9)59- 54... 

Scheme 13).16 The presence of the BMes2 group induces a moderate downfield shift of the 31P NMR signal (by 2-3 ppm), suggesting only weak, if any, electron transfer from phosphorus to boron. Consistently, the UV-vis absorption band for 16a (/lmax 332 nm) is blue shifted compared with that of the related NB system (354 nm). 

Disilyne 76 is emerald green in the solid state and shows two allowed n- n absorption bands in hexane at 259 (e 10300) and 328 (e 5800) nm and two forbidden n- n absorption bands at 483 (e 120) and 690 (e 14) nm.41 Theoretical calculations for 76 at the HF/6-311G(d)//B3LYP/6-31G(d) level have shown that HOMO and HOMO-1 are two split n orbitals and LUMO and LUMO+ 1 are two split lowest 7i orbitals. The out-of-plane n orbitals HOMO and LUMO+ 1 are represented by pure (p -p )7i orbitals, whereas the in-plane n orbitals HOMO-1 and LUMO are represented mainly by (py-py)n orbitals with a weak contribution of the a (Si-Si) orbital of the central bond. The presence of the nondegenerate n and ti molecular orbitals in 76 is responsible for the UV-vis absorption band feature of 76. 

Early proposals suggested [72] that catalase contains a p-oxo-bis(p-carboxylato)-dimanganese core. The UV-Vis spectra of this structural motif present in model complexes exhibit 480-520 nm d-d absorptions [73] similar to the UV-Vis absorption bands of manganese catalases. The EPR studies of oxidized T. ther-mophilus catalase [74] also suggested a MnIIIMnI" p-oxo-bis(p-carboxy 1 ato) core as a possible structural motif for the active site. 

The quantitative difference in adsorption behavior of linear polymers between alkaline and acidic conditions can be verified from surface plasmon resonance (SPR) results [111]. As seen in Fig. 6, the adsorption kinetics change along any profile of rapid saturation, gradual increase after rapid increase or gradual increase, depending on the type of linear polymers. The equilibrium of adsorption is reached faster for NaPGA and NaHA than for DNA. However, the film at equilibrium is thicker at acidic condition than at alkaline condition. The quantitative estimation of adsorption of DNA on dendrimer SAMs can be also carried out from the intensity increase of a UV-vis absorption band at 258.8 nm [110]. 

The on-line detection of TNT and some of its breakdown products during their SC-CO2 extraction out of contaminated soils was simulated under different pressures and temperatures. The nitroaromatic compounds dissolved in sc-C02 were identified by their characteristic UV-VIS absorption bands. A quantification of the analytes was possible for concentrations lower than 1 ppm. 

The term solvatochromism is used to deseribe the pronouneed ehange in position (and sometimes intensity) of a UV/Vis absorption band that aeeompanies a ehange in the polarity of the medium. A hypsoehromie (or blue) shift with inereasing solvent polarity is usually ealled negative solvatochromism. The eorresponding bathoehromie (or red) shift is termed positive solvatochromism. What kind of eompounds exhibit this response to ehanges in solvent polarity ... 

It should be mentioned that solvent effects on the intensity of UV/Vis absorption bands cannot be interpreted in a simple qualitative fashion as is the case for the band position shifts [85, 308, 309, 321-323]. 

The UV-Vis Absorption Bands for the M(TCPyP) Species in Acetonitrile Solution and the Respective log (e) = Molar Absorptivity. 

Again, the challenge involves a suitable detection system. As illustrated in Fig. 1, many radicals produced upon pulse irradiation of an aqueous system have UV/Vis absorption bands that can be monitored. Clearly, it is suitable to directly follow absorbance changes in the hydrated electron and the carbonate radical anion, with absorption maxima of 715 nm and 600 nm respectively, through the use of an UV/vis spectrophotometer with fast response time. The OH radical. 

Initial reports concerning the protonation behavior of corrole involved claims of having observed both a mono- and a diprotonated species. In the case of the monoprotonated macrocycle, the UV-vis absorption bands remained relatively unchanged compared to those of the free-base species. In the case of diprotonated corroles, on the other hand, the second protonation event was presumed to occur at one of the meso carbons, resulting in a disruption of the n-electron conjugation. This latter conclusion was based upon the dramatic changes observed to occur in the UV-vis absorption spectrum. 

The me o-phenyl-substituted sapphyrins 5.33-5.35, 5.37, 5.45-5.47, and 5.49-5.50 (as HCl salts) display UV-vis absorption bands that resemble qualitatively those of the better studied all P-alkyl-substituted sapphyrins. For instance, 10,15-diphenylsapphyrin 5.33, when dissolved in CH2CI2, exhibits a Soret band that is bathochromically shifted by ca. 5-10 nm relative to that of the meso-unsubstituted alkylsapphyrins to 462 nm. A further bathochromic shift of ca. 30 nm (out to A-max = 484 nm) is observed for the Soret band of the bis-HCl salt of wc50-tetraphenylsapphyrin 5.50. Each of the phenyl-substituted sapphyrin salts also exhibit two to three (as opposed to four for alkyl-sapphyrin salts) weak Q-type bands in their absorption spectra. These bands fall in the 625-780 nm region and are thus red-shifted relative to the corresponding bands of alkyl-substituted sapphyrins. 

H NMR spectroscopic analysis (e.g., 8cH-inner = —16.0 ppm 5cH-outer = 13.8 and 14.7 ppm, in CF3CO2D). Macrocycle 7.85 also exhibits UV-vis absorption bands characteristic of highly conjugated porphyrin-related annulenes. For instance, in 5% TFA in CH2CI2, system 7.85 exhibits one fairly intense Soret-like band at 667 nm... 

The new UV-Vis absorption band at 425 nm (Fig. 48) was taken as evidence in support of participation of benzidine, the tail-to-tail dimer, in the polymerization process. 

Figure 18. Diterpenes from some old- and new-world montane Salvia spp showing convergence of molecular characters leading to yellow and UV-A/B absorbing chromophores. UV-Vis absorption bands (log e) are shown when known. For references see text.

In analogy with the case of rotational strength, the dipole strength D representing the transition probability of the UV—Vis absorption band is estimated from the observed spectra, as follows ... 

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