Absorption spectra various solvents

The preceding empirical measures have taken chemical reactions as model processes. Now we consider a different class of model process, namely, a transition from one energy level to another within a molecule. The various forms of spectroscopy allow us to observe these transitions thus, electronic transitions give rise to ultraviolet—visible absorption spectra and fluorescence spectra. Because of solute-solvent interactions, the electronic energy levels of a solute are influenced by the solvent in which it is dissolved therefore, the absorption and fluorescence spectra contain information about the solute-solvent interactions. A change in electronic absorption spectrum caused by a change in the solvent is called solvatochromism. 

When the silver nanocrystals are organized in a 2D superlattice, the plasmon peak is shifted toward an energy lower than that obtained in solution (Fig. 6). The covered support is washed with hexane, and the nanoparticles are dispersed again in the solvent. The absorption spectrum of the latter solution is similar to that used to cover the support (free particles in hexane). This clearly indicates that the shift in the absorption spectrum of nanosized silver particles is due to their self-organization on the support. The bandwidth of the plasmon peak (1.3 eV) obtained after deposition is larger than that in solution (0.9 eV). This can be attributed to a change in the dielectric constant of the composite medium. Similar behavior is observed for various nanocrystal sizes (from 3 to 8 nm). 

Fig. 3. Ultraviolet absorption spectrum of p-f-butylphenol in various solvents. The absorbance values are arbitrarily shifted vertically for purposes of clarity. — Water ...

Forster (1959) classifies the qualitative features based on which one can distinguish the various modes of energy transfer. Mainly, only collisional transfer depends on solvent viscosity (vide infra), whereas complexing between the donor and acceptor changes the absorption spectrum. On the other hand, the sensitizer lifetime decreases for the long-range resonant transfer process, whereas it should be unchanged for the trivial process. 

The values of ftot for various benzotriazole compounds in a range of solvents are listed in Table II. Values of the fluorescence quantum yield for TIN and TINS, corrected for the absorbance by their non-fluorescent, planar conformers at the excitation wavelength, are listed in Table III. In all the benzotriazole solutions examined, maximum fluorescence emission was observed at about 400 nm indicating that this emission originates from the non proton-transferred species. This was confirmed by examination of the fluorescence excitation spectrum which corresponds to the absorption spectrum of the non-planar form of the molecule. 

The absorption spectrum of a pharmaceutical substance depends partially upon the solvent that has been employed to solubilize the substance. A drug may absorb a miximum of radiant energy at a particular wavelength in one solvent but shall absorb practically little at the same wavelength in another solvent. These apparent changes in spectrum are exclusively due to various characteristic features, namely ... 

It should be recalled that, in polar rigid media, excitation on the red-edge of the absorption spectrum causes a red-shift of the fluorescence spectrum with respect to that observed on excitation in the bulk of the absorption spectrum (see the explanation of the red-edge effect in Section 3.5.1). Such a red-shift is still observable if the solvent relaxation competes with the fluorescence decay, but it disappears in fluid solutions because of dynamic equilibrium among the various solvation sites. 

In the present paper, the effect of various solvents on the absorption spectrum and the fluorescence spectmm of a heterocychc compound was investigated. 

Anion solvation has been studied by observing the shift in the absorption spectrum of the benzophenone anion in various solvents and as a function of temperature. The benzo-phenone anion was formed from the reaction of the benzophenone molecule and a precursor to the solvated electron. Approximately 0.25 M benzophenone is put into the solution so that all the presolvated electrons will react with the benzophenone and virtually none will form the solvated electron. This process occurs much more quickly than the solvation processes that are observed [14,20]. 

Absorption spectra of peridinin in different solvents are shown in Fig. 2a. In the nonpolar solvent M-hexane, the absorption spectrum exhibits the well-resolved structure of vibrational bands of the strongly allowed S0-S2 transition with the 0-0 peak located at 485 nm. In polar solvents, however, the vibrational structure is lost and the absorption band is significantly wider. In addition, there are also differences between the various polar solvents. Although the loss of vibrational structure is obvious, a hint of shoulder is still preserved in methanol and acetonitrile, but in ethylene glycol and glycerol the absorption spectrum is completely structureless with a broad red tail extending beyond 600 nm. 

The 7e,7e-diiodide was isolated as the 1 1 mixture of the tetrafluoroborate and the triiodide salt. The electronic absorption spectra of the diiodide in various solvents are identical to the spectrum of the iodine-free compound1. 

Because the 2570 A band of phenylalanine is weak, it is often obscured in proteins by the much stronger tyrosine and tryptophan absorptions. It is occasionally visualized in protein spectra as ripples (fine structure) in the spectral region 2500-2700 A. These ripples can be amplified by the difference spectral technique, as is shown in Fig. 13. A typical phenylalanine difference spectrum, obtained in a comparison of the isoelectric amino acid with a solution of the same concentration at pH 1 is shown in Fig. 12. Difference spectra for phenylalanine in various solvents have been measured by Bigelow and Geschwind (1960), Yanari and Bovey (1960), and Donovan et al. (1961). Fluorescence activation and emission spectra for phenylalanine were measured by Teale and Weber (1957). 

It is frequently assumed that the absorption spectrum of a test substance will accurately represent its activation or action spectrum because only absorbed radiation can bring about a photochemical change. Frequently neglected are solvent (bathochromic or hypsochromic) or matrix effects such as polarity, pH, complexation, dimerization, binding, self-filtering, and quantum efficiency differences between various absorption bands, etc., which may occur. 

The effects of the mixed supersonic expansion of CDMA with various solvent molecules (such as cyclohexane, carbon tetrachloride, acetone, acetonitrile, methanol, dichloromethane and chloroform) on the emission spectra have been investigated by Phillips and co-workers [82d[. The cluster size distribution was varied by changing the nozzle temperature and the partial pressure of the solvent. Two emission components were observed in each case. The long-wave emission was attributed to dimers (which can be isolated or solvated) and to monomer complexed with chloroform or dichloromethane (of unknown stoichiometry). On the other hand, it has been reported by Bernstein and co-workers [84] that CDMA forms with acetonitrile two kinds of 1 1 complexes of different geometry. The first cluster has a structured excitation spectrum, similar to that of the bare molecule, but blue shifted by about 252 cm . The second exhibits a broad excitation spectrum with some resolvable features between 31400 and 31 600 cm (Table 2). The complexes show different fluorescence spectra excitation into the broad absorption leads to the red-shifted emission with respect to that of the monomer (Figure 8) and of the blue ... 

The absorption spectrum of phenol was measured in various. . . mixed solvents,. . . With increasing concentration of dioxane. .. [a] new absorption. . . appears. . , which seems to be due to hydrogen bridged phenol molecules,, the anomalous phenomenon, is attributable to H bonding between solute and proton acceptor molecules, S. NAGAKURA and H. BABA Tokyo, Japan, 1952... 

The absorption spectrum of l-phenylazo-2-naphthol in various solvents and the spectra of the photoinduced colored species at low temperature generated by the exposure of this compound to light at various wavelengths was studied in detail, For any o-hydroxyazo compound, e.g., l-phenylazo-2-naphthol, the combined results of tautomerization and rotation around single and double bonds lead to the eight configurations ATI, AT2, ACl, AC2, HTl, HT2, HCl, and HC2, where H and A represent the hydrazone and azo forms, respectively, and T and C denote the trans and cis configurations, respectively. 

The UV absorption values in various solvents are expressed in E 1%/lcm and e for quantification purposes. The values given in the table for each spectrum are those obtained in commercially available pure substance and checked on several photometers. Anyone who is familiar with this type of material will know that the values may differ slightly from those of other investigators. 

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