Effect on absorption spectra

An intramolecular charge transfer toward C-5 has been proposed (77) to rationalize the ultraviolet spectra observed for 2-amino-5-R-thiazoles where R is a strong electron attractor. Ultraviolet spectra of a series of 2-amino-4-p-R-phenylthiazoles (12) and 2-amino-5-p-R-phenylthiazoles (13) were recorded in alcoholic solution (73), but, reported in an article on pK studies, remained undiscussed. Solvent effects on absorption spectra of 2-acetamido and 2-aminothiazoles have been studied (92). 

All those spectral changes which arise from alteration of the chemical nature of the chromophore-containing molecules by the medium, such as proton or electron transfer between solvent and solute, solvent-dependent aggregation, ionization, complexation, or isomerization equilibria lie outside the scope of this chapter. Theories of solvent effects on absorption spectra assume principally that the chemical states of the isolated and solvated chromophore-containing molecules are the same and treat these effects only as a physical perturbation of the relevant molecular states of the chromophores [435-437]. 

Thus, solvent effects on absorption spectra can be used to provide information about solute-solvent interactions [1-4]. On the other hand, in order to minimize these effects, it would be preferable to record absorption spectra in less interacting nonpolar solvents, such as hydrocarbons, whenever solubility permits. Suitable choice of a spectral solvent may be facilitated by consulting Tables A-4 (UV/Vis), A-5 (IR), A-6 ( H NMR), and A-7 NMR) in the Appendix, which list some of the more common solvents and their absorption properties. 

Substituent Effect on Absorption Spectra of Benzo[6]quinolizinium Salts... 

V. Luzhkov and A. Warshel, Microscopic calculations of solvent effects on absorption spectra of conjugated molecules, J. Am. Chem. Soc., 113 (1991), 4491 99. 

H.P. Braun, M.E. Michel-Beyerle, J. Breton, S. Buchanan, and H. Michel, Electric field effect on absorption spectra of reaction centers of Rb. sphaeroides and Rps. viridis, FEBS Lett. 221 221 (1987). 

Parac M et al (2010) QM/MM calculation of solvent effects on absorption spectra of guanine. J Comput Chem 31 90-106... 

In Sec. 2 the effective mass equation is introduced and the band structure is discussed with a special emphasis on an Aharonov-Bohm effect. Optical absorption spectra are discussed in Sec. 3. A lattice instability, in particular induced by a magnetic field perpendicular to the tube axis, is discussed in Sec. 4 and magnetic properties of ensembles of CNTs are discussed in Sec. 5. 

These spectra show even fewer features than those of the palladium catalysts. Absorption takes place almost exclusively in the region 2000-2100 cm-1. There are some weak bands below 2000 cm-1, but our experimental method did not allow us to determine their frequencies with reasonable accuracy. It is clear that also with the iridium catalysts the particle size has an effect on the spectra. The spectrum of Ir-8 shows only one intense band at 2048 cm-1, whereas the other two have additional bands at higher frequencies. There is also a marked dependence of the intensity of the 2048 cm-1 band on the CO pressure, especially in the case of Ir-37 and Ir-100. We shall not try to interpret the CO spectra of the iridium samples, as we consider the data available insufficient for the purpose. 

Owing to experimental difficulties, knowledge of aggregation effects in alkaline dithionite solutions of leuco vat dyes is sporadic [20,21]. Investigations based on absorption spectra have shown that, depending on concentration and temperature, planar polycyclic molecules such as the violanthrone derivatives Cl Vat Blues 19, 20 and 22 and the perylene tetracarboxydiimide derivatives Cl Vat Reds 23 and 32 are mainly present as monomers or dimers in leuco vat solutions. Violanthrones that do not have a coplanar structure because of the presence of... 

Shifts in absorption spectra due to the effect of substitution or a change in environment (e.g. solvent) will be discussed in Chapter 3, together with the effects on emission spectra. Note that a shift to longer wavelengths is called a bathochromic shift (informally referred to as a red-shift). A shift to shorter wavelengths is called a hypsochromic shift (informally referred to as a blue-shift). An increase in the molar absorption coefficient is called the hyperchromic effect, whereas the opposite is the hypochromic effect. 

Dimerization effects on absorption and emission spectra of TCP are shown in Figures 1 and 2. Similar effects are observed upon dimerization of ZnTCP (12), formation of [TPPS/TTAP] and... 

The dipole moment of an excited state can be estimated from an analysis of solvent effects on absorption and emission spectra the... 

Porter has correlated solvent shifts on absorption spectra with the photoreactivity of substituted benzophenones.365 He has noted red shifts for the unreactive substituted ketones upon shifting from cyclohexane to 2-propanol, which effect he ascribes to absorption into an intramolecular charge-transfer band which would be stabilized by solvent polarity. He reasons further that the charge-transfer nature of... 

Some other polymers of the same type with valence (I) were also prepared (Fig. 17). They exhibit almost the same structure, except that halides are replaced by diphosphine ligands (diphos) such as bis(diphenylphosphino) butane (dppb), bis(diphenylphosphino)pentane (dpppen), and bis(diphenyl-phosphino)hexane (dpph).36,40 Again a model complex, compound 25, was studied as reference (Fig. 17). The electronic spectra exhibit an absorption band near 480 nm. These coordination materials are not luminescent at room temperature but are luminescent in solution in butyronitrile at low temperature (i.e., 77 K). Density functional theory (DFT) calculations showed that luminescence arises from a da-da triplet excited state. In these polymers, the nature of the phosphine ligand has a crucial effect on absorption and emission bands. Such behavior is explained by the increase in electronic density on the... 

The first published work on the pressure dependence of optical spectra of solids seems to be of Paetzold (1940), who has studied the effect of pressure on absorption spectra of praseodymium nitrate, ruby, and other minerals between 1938 and 1939. To generate a maximum pressure of 0.1 GPa the samples were subjected to pressurised nitrogen. Using the same high pressure apparatus, Hellwege and Schrock-Vietor (1955) studied the pressure dependence of the absorption spectra of EuZn-nitrate. These authors, for the first time, applied the crystal-field Hamiltonian formalism for the analysis of the high pressure spectroscopic results. 

Several examples have shown that specific interactions such as hydrogen bonding interactions should be considered as one of the intrinsic aspects of solvent effects on absorption or fluorescence spectra. 

The ligand field transitions of tetrahedrally coordinated Fe3 are Laporte-allowed. Consequently, small amounts of tetrahedrally coordinated Fe3 may have a large effect on the spectra of iron-bearing clays. In the optical spectrum of nontronite (4), the small amount of tetrahedral Fe3 gives an intense absorption band near 23,000 cm 1 that is assigned to the 6A- - Aj, E transition. 

Hazen, R. M., Bell, P. M. Mao, H.-K. (1978) Effects of compositional variation on absorption spectra of lunar pyroxenes. Proc. 9th Lunar Planet. Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 9 (Pergamon Press, New York), pp. 2919-34. 

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