Solvent spectral shift

To circumvent this difficulty, Luzhkov and Warshel derived a semiclassical approach in which the computed solvent spectral shift is corrected for the difference in the polarization effects in the ground and excited states ... 

Table 6 Computed Solvent Spectral Shifts and Changes in Solvation Energy for the n - >17 Electronic Transition of Acetone (cm ) ...

A solubihty parameter of 24.5-24.7 MPa / [12.0-12.1 (cal/cm ) ] has been calculated for PVF using room temperature swelling data (69). The polymer lost solvent to evaporation more rapidly than free solvent alone when exposed to air. This was ascribed to reestabUshment of favorable dipole—dipole interactions within the polymer. Infrared spectral shifts for poly(methyl methacrylate) in PVF have been interpreted as evidence of favorable acid—base interactions involving the H from CHF units (70). This is consistent with the greater absorption of pyridine than methyl acetate despite a closer solubihty parameter match with methyl acetate. 

The role of specific interactions in the plasticization of PVC has been proposed from work on specific interactions of esters in solvents (eg, hydrogenated chlorocarbons) (13), work on blends of polyesters with PVC (14—19), and work on plasticized PVC itself (20—23). Modes of iateraction between the carbonyl functionaHty of the plasticizer ester or polyester were proposed, mostly on the basis of results from Fourier transform infrared spectroscopy (ftir). Shifts in the absorption frequency of the carbonyl group of the plasticizer ester to lower wave number, indicative of a reduction in polarity (ie, some iateraction between this functionaHty and the polymer) have been reported (20—22). Work performed with dibutyl phthalate (22) suggests an optimum concentration at which such iateractions are maximized. Spectral shifts are in the range 3—8 cm . Similar shifts have also been reported in blends of PVC with polyesters (14—20), again showing a concentration dependence of the shift to lower wave number of the ester carbonyl absorption frequency. 

The basic premise of Kamlet and Taft is that attractive solute—solvent interactions can be represented as a linear combination of a nonspecific dipolarity/polarizability effect and a specific H-bond formation effect, this latter being divisible into solute H-bond donor (HBD)-solvent H-bond acceptor (HB A) interactions and the converse possibility. To establish the dipolarity/polarizability scale, a solvent set was chosen with neither HBD nor HBA properties, and the spectral shifts of numerous solvatochromic dyes in these solvents were measured. These shifts, Av, were related to a dipolarity/polarizability parameter ir by Av = stt. The quantity ir was... 

The spectral absorptions shift to longer wavelengths as the solvent polarity increases. However, care must be taken to distinguish them from the spectral shifts due to deprotonation. 

While excited-state properties of monomeric carotenoids in organic solvents have been the subject of numerous experimental and theoretical studies (Polfvka and Sundstrom 2004), considerably less is known about excited states of carotenoid aggregates. Most of the knowledge gathered so far stems from studies of aggregation-induced spectral shifts of absorption bands of carotenoid aggregates that are explained in terms of excitonic interaction between the molecules in the aggregate. 

Using the Onsager model, the function Av-l(t) can be calculated for all time domains of dielectric relaxation of solvents measured experimentally for commonly used liquids (see, for example, [39]). Such simulations, for example, give for alcohols, at least, three different time components of spectral shift during relaxation, which are due to appropriate time domains of solvents relaxation. 

The same equation was introduced by Suppan, where Av /was treated as spectral shift of the probe spectra in two different solvents [60]. 

When we perform experiment in such way that there is no interference of H-bonds or these bonds are stable and structure of solvent also does not varies essentially, solvatochromic plot demonstrates very good linearity as shown, for example, for some naphthylamine derivatives in ethanol-water mixtures. The linearity of solvatochromic plots is often regarded as an evidence for the dominant importance of nonspecific universal intermolecular interaction in the spectral shifts. Specific solvent effects lead to essential deviation of measured points from this linear plot. 

The method of revealing of H-bonds is very simple an addition of low concentration, 1-3% of molar fraction, of alcohols (ethanol, methanol) to the solution in neutral solvent (CH, for example) results in a substantial spectral shift. Further addition of alcohols, up to 100%, gives much smaller shifts. A small percentage of alcohol may cause 50-80% of total spectral shift. Upon addition of the trace quantities of alcohol, one sees that the intensity of the initial spectrum is decreased, and new red-shifted spectrum appears. The appearance of new spectral component is a characteristic of specific solvent effects. Because the specific spectral shifts occur only at low concentration of alcohol, this effect is probably attributed to H-bonding to electronegative group in the molecule. The next experiment, which can support this conclusion, is an addition of aprotic solvent, for example,... 

Ware WR, Lee SK, Brant GJ, Chow PP (1970) Nanosecond time-resolved emission spectroscopy spectral shifts due to solvent-solute relaxation. J Chem Phys 54 4729 1737... 

Ware WR, Chow PP, Lee SK (1968) Time-resolved nanosecond emission spectroscopy spectral shifts due to solvent-solutes relaxation. Chem Phys Lett 2(6) 356-358... 

In the preparation of 15 nm core-shell fluorescent silica particles, Ow et al. (2004) reported that the naked core (2.2 nm) alone produced a fluorescence intensity of less than the free dye in solution, presumably due to dye quenching. However, upon addition of the outer silica shell around the core, the brightness of the particles increased to 30 times that of the free dye (using tetramethylrhodamine-5-(and 6)-isothiocyanate (TRITC)). They speculate that shell may protect the core from solvent effects, as evidenced by a lack of spectral shift upon changing the solvent in which the particles are suspended. 

In the OFRR, the wall thickness is important, as it determines the fraction of the light in the core that interacts evanescently with the gain medium when the solvent is of low RI. To precisely characterize the OFRR thickness noninvasively, we use the method developed previously22, in which various concentrations of water-ethanol mixtures are passed through the OFRR, and the WGM spectral shift in response to RI changes in the core is plotted as demonstrated in Fig. 19.4b. By matching the experimental sensitivity results with those obtained from our... 

Solvation properties, of supercritical solvents, 14 80-81 Solvatochromic materials, 22 708t Solvatochromic probes, 26 853—855 Solvatochromic spectral shifts, 23 96 Solvatochromy, 20 517 Solvay, 7 641 Solvay process, 15 63... 

Fig. 31.— 13C-N.m.r. Spectra of Native Neisseria meningitidis Serogroup A Polysaccharide (A 27 and 28) and O-Deacetylated Product (B 28). [Solvent, D20 at 37° the spectral-shift axis is based on external tetramethylsilane (8C = 0).]...

X0 is the value of the property in the gas phase. (In practice, X and X0 are often the logarithm of the property in question.) The parameters a and p are measures of a solvent s ability to donate and accept hydrogen bonds, respectively, and tt is an index of its polarity/polarizability. They were initially assigned on the basis of ultraviolet spectral shifts of certain dyes in a variety of solvents, and hence were labeled solvatochromic parameters.186"188... 

Vincent M, Gallay J, Demchenko AP (1995) Solvent relaxation around the excited-state of indole - analysis of fluorescence lifetime distributions and time-dependence spectral shifts. J Phys Chem 99 14931-14941... 

Ware W. R., Lee S. K., Brant G. J. and Chow P. P. (1971) Nanosecond Time-Resolved Emission Spectroscopy Spectral Shifts due to Solvent-Excited Solute Relaxation, J. Chem. Phys. 54, 4729-4737. 

Pi-complexing is most commonly used to rationalize effects observed in aromatic solvents. The most frequent evidence cited is magnetic anisotropy effects on chemical shifts in the solute molecule. As was the case for hydrogen bonding no quantitative correlations with substantive parameters such as ultraviolet spectral shifts have been attempted. 

Baur, M., Nicol, M. Solvent Stark Effect and Spectral Shifts. J. Chem. Phys. 44, 3337 (1966). 

The dipole-dipole interactions of the fluorophore in the electronic excited state with the surrounding groups of atoms in the protein molecule or with solvent molecules give rise to considerable shifts of the fluorescence spectra during the relaxation process. These spectral shifts may be observed directly by time-resolved spectroscopic methods. They may be also studied by steady-state spectroscopic methods, but in this case additional data must be obtained by varying factors that affect the ratio between tf and xp. 

There are substantial difficulties in the interpretation of temperature-dependent shifts of protein spectra because of the thermal lability of proteins and the possibility of temperature-dependent conformational transitions. Low-temperature studies in aqueous solutions revealed that for many of the proteins investigated the observed shifts of the fluorescence spectra within narrow temperature ranges were probably the result of cooperative conformational transitions, and not of relaxational shifts/100 1 Spectral shifts have also been observed for proteins in glass-forming solvents, 01) but here there arise difficulties associated with the possible effects of viscous solvents on the protein dynamics. 

The fluorescent probe 2,6-TNS and other similar aminonaphthalene derivatives (1,8-ANS, DNS) were considered to be indicators of the polarity of protein molecules, and they were assumed to be bound only to hydrophobic sites on the protein surface. The detection of considerable spectral shifts with red-edge excitation has shown that the reason for the observed short-wavelength location of the spectra of these probes when complexed to proteins is not the hydrophobicity of their environment (or, at least, not only this) but the absence of dipole-relaxational equilibrium on the nanosecond time scale. Therefore, liquid solvents with different polarities cannot be considered to simulate the environment of fluorescent probes in proteins. 

The isolated enantiomers S (M ) and R (Mr) of a chiral molecule M exhibit the same spectral features since their physical properties are identical. However, their aggregation with a chiral chromophore of defined configuration (Cr/s) leads to the formation of two diastereomeric complexes with different spectral properties, i.e., and [C /yM ]. The lcR2PI spectroscopy is able to discriminate between Mj and by measuring the spectral shift of the diastereomeric [C /yM ] and [Cj5/5-Mj ] complexes with respect to that of the bare chromophore Cr/s- It is convenient to define the diastereomeric clusters as homochiral when the chromophore and the solvent have the same configuration, and heterochiral in the opposite case. 

The opposite direction of spectral shift with solvent polarity is observed for the spiro-oxazine [4] and naphthopyran mero-forms and this is generally accepted to infer a quinoidal HOMO and a zwitterionic LUMO state in their cases. This shift is shown also in Fig. 7b for a naphthopyran TT isomer (CHR2). Of course, H-bonding and other specific interactions will also affect the position of the mero-form spectral maximum. In the case of the substituted BIPS, spiro-oxazine, and CHR2, there is evidence to support their respective assignments to a zwitterionic and quinoidal forms, including x-ray [36,80-85] and NMR [36,55,86-88] data. 

We have found that emission spectra of the cooperatively excited ADF from upper electronic states and of the one quantum excited PF are different. ADF spectrum is shifted in the longwave direction with respect to PF spectrum (see Table II). The shift effect depends on solvent type. ADF spectral shift is most considerable and comprises 500 cm"l (see Fig. 1) for the case of ZnTPP in decane. 

The emitting species was found to be the singlet-excited state of 3-aminophthlate ion in both protic and aprotic solvents. This identification was made based on the equivalence of the chemiluminescence spectrum of luminol and the fluorescence spectrum of 3-AP ion . In different reaction media, slightly different maximum chemiluminescence wavelengths are observed (Table 2). The spectral shift observed when the system changes from aqueous media to DMSO or other aprotic solvents can be ascribed to a quinoidal form of 3-aminophthalate (26) formed in aprotic solvents (Scheme 15). ... 

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