Spectral, band shifts

Binding energies of complexes, equilibrium constants, spectral band shift in complexing etc. have been determined. 

Over the last few years, the development of solvents of desired properties with a particular use in mind has been challenging. To evaluate the behaviour of a liquid as solvent, it is necessary to understand the solvation interactions at molecular level. In this vein, it is of interest to quantify its most relevant molecular-microscopic solvent properties, which determine how it will interact with potential solutes. An appropriate method to study solute-solvent interactions is the use of solvatochromic indicators that reflect the specific and non-specific solute-solvent interactions on the UV-Vis spectral band shifts. In this sense, a number of empirical solvatochromic parameters have been proposed to quantify molecular-microscopic solvent properties. In most cases, only one indicator is used to build the respective scale. Among these, the E (30) parameter proposed by Dimroth and Reichardt [23] to measure solvent dipolarity/polarisability which is also sensitive to the solvent s hydrogen-bond donor capability. On the other hand, the n, a and P (Kamlet, Abboud and Taft)... 

Tanner PA, Fu L, Cheng B-M (2009) Spectral band shifts in the electronic spectra of rare earth sesquioxide nanomaterials doped with europium. J Phys Chem C 113 10773-10779... 

The spectral band shifts were also related to solvent parameter (p(s, n) which is given as follows [15]... 

Solvent Influence. Solvent nature has been found to influence absorption spectra, but fluorescence is substantiaHy less sensitive (9,58). Sensitivity to solvent media is one of the main characteristics of unsymmetrical dyes, especiaHy the merocyanines (59). Some dyes manifest positive solvatochromic effects (60) the band maximum is bathochromicaHy shifted as solvent polarity increases. Other dyes, eg, highly unsymmetrical ones, exhibit negative solvatochromicity, and the absorption band is blue-shifted on passing from nonpolar to highly polar solvent (59). In addition, solvents can lead to changes in intensity and shape of spectral bands (58). 

The spectral bands corresponding to TaF6 and TaF72 in molten state are shifted towards higher frequencies, compared to their position in corresponding spectra obtained for the crystals. This phenomenon is common and is observed for other systems as well. 

Figure 3.17 presents ps-TR spectra of the olehnic C=C Raman band region (a) and the low wavenumber anti-Stokes and Stokes region (b) of Si-rra i-stilbene in chloroform solution obtained at selected time delays upto 100 ps. Inspection of Figure 3.17 (a) shows that the Raman bandwidths narrow and the band positions up-shift for the olehnic C=C stretch Raman band over the hrst 20-30 ps. Similarly, the ratios of the Raman intensity in the anti-Stokes and Stokes Raman bands in the low frequency region also vary noticeably in the hrst 20-30 ps. In order to better understand the time-dependent changes in the Raman band positions and anti-Stokes/Stokes intensity ratios, a least squares htting of Lorentzian band shapes to the spectral bands of interest was performed to determine the Raman band positions for the olehnic... 

As well known, the electronic spectral bands show shifts as a whole in solvents of different nature. This phenomenon called solvatochromism is directly connected with the intermolecular interactions in the solute-solvent system. 

Photoexcitation of Cu rare-gas films in the region of the 2P 2S absorption band produces intense narrow emissions bands showing large spectral red shifts as seen in Figure 4,(34). 

Most of the complexes to be described here have trigonal symmetry. For a trigonal center, the splitting of the spectral bands due to the lifting of orientational degeneracy is described by two parameters, A1 and A2. The parameter A is proportional to the hydrostatic component of the stress and gives rise to a shift in frequency that is independent of the stress direction, whereas A2 gives rise to a shift that depends on the orientation of the center. 

The concept of dynamic silver clusters capable to transfer between molecules was also pointed out recently by Ras et al. for silver clusters prepared by photoactivation using PM A A as scaffold [20], Every specific initial ratio of silver ions to methacrylate unit, Ag+ MAA, results in distinct spectral bands (Fig. 12a, b). Thus, an initial ratio 0.5 1 gives an absorption band at 503 nm, whereas a ratio 3 1 gives a band at 530 nm. The shuttle effect was proven when for a given silver cluster solution with ratio 3 1 and absorption at 530 nm, a blue shift was achieved by the addition of pure PMAA. For instance if the added amount of polymer decreases the ratio Ag+ MAA from 3 1 to 0.5 1, the new optical band will match exactly with the band corresponding to a solution with initial ratio 0.5 1, that is 503 nm (Fig. 12c). The explanation given for this blue shift was the redistribution of the existent silver clusters in PMAA chains over the newly available PMAA chains, in other words that the clusters shuttle from partly clusters-filled chains to empty ones. 

In 1899, Lowry discovered the change in the rotatory power over time of a solution of nitrocamphor in benzene, an effect previously encountered only with aqueous solution of sugars. He named this effect "mutarotation," and its discovery was taken as a prominent achievement for Armstrong s laboratory research group. 50 Lowry ascribed the phenomenon to tautomeric conversion (from a CH-N02 form to a C = NO-OH form), that is, the shift of a hydrogen atom and the shift of a double bond. In 1909, he and Desch concluded that this reversible transformation occurs very quickly because they could not find an ultraviolet absorption spectral band characteristic of either isomer. 51 But what triggered this reversible transformation ... 

For NP2 and NP3 at pH 7.5, the shift in Soret band positions of the NO complexes for the two oxidation states is somewhat larger—8-10 nm, from 421-423 to 413 nm for the Fe(III) and Fe(II) complexes, respectively (50). However, in contrast to NPl-NO (49) and NP4-NO (50), at pH 5.5 NP2-NO and NP3-NO show very different spectral shifts upon electrochemical reduction, as shown in Fig. 6c for NP3-NO. The Soret band shifts to 395 nm, and both the wavelength maximum and shape of the Soret band are typical of five-coordinate heme-NO centers, including guanylyl cyclase, upon binding NO (53, 54). The reduced forms of both NP2-NO and NP3-NO exhibit similar pH dependence of the absorption spectra, whereas NPl-NO and NP4-NO do not show any pH dependence of their absorption spectra over the pH range 5.5-7.5 (50). 

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