Solvatochromic molecule

Combining the idea of solvent-induced changes in molecular structure with the concept of a solvent continuum around the solvatochromic molecule, a micro-structural model of solvatochromism has been developed by Dahne et al., which reproduces, qualitatively correctly and quantitatively satisfactorily, the solvatochromic behavior of simple merocyanine dyes [95b], The results obtained with this model for 5-(dimethylamino)penta-2,4-dienal are in good agreement with the solvent-dependent experimental data such as transition energies, oscillator strengths, r-electron densities, and r-bond energies [95b] cf. also [326, 327],... 

Figure 1. Two-level picture corresponds to the second-harmonic generation (SHG) process in the gas phase and in polar solvent a) positively solvatochromic molecule, b) negatively solvatochromic molecule...

To determine the polarity of the microenvironment of polymers, polymer labelled with solvatochromic reporters were prepared, either by (1) copolymerization with solvatochromic monomers 2 >3 or (2) polymer analogous reactions (e.g., the reaction of copolymer acUve esters with primary amino groups of the solvatochromic molecule or alkylation reaction of PVIm and cross-linked polymers with solvatochromic mole-cule.34i37 The properties of the microenvironment of polymers were studied by the shift and shape of band in electronic spectra of a solvatochromic reporter molecule embedded in polymers. 

The concept of reduced solvation of the solvatochromic chromo-phore bound to polymer chain with solvent molecules and preferential intramolecular solvation of the solvatochromic molecule with side subtituent of the polymer backbone was supported by means of time-resolved absorption spectrometry of the merocyanines bonded to poly/ methyl methacrylate/. ... 

Figure 10.3.4. Examples of the solvatochromic molecules a) positive solvatochromic paranitroaniline, b) negative Reichardt s dye and c) inversely solvatochromic Brooker s merocyjanine.

Based on the presented research it can be stated, that the excited state line width parameter has an important influence on the CT2pa in the case of the moderate positive solvatochromic molecules, as the individual parameters may cancel each other. In the case of strongly negative solvatochromic molecule, the T probably just confirmed the tendency established by the three other parameters. 

Donor strengths, taken from ref. 207b, based upon the solvent effect on the symmetric stretching frequency of the soft Lewis acid HgBr2. Gutmann s donor number taken from ref 207b, based upon AHr for the process of coordination of an isolated solvent molecule to the moderately hard SbCL molecule in dichioroethane. ° Bulk donor number calculated as described in ref 209 from the solvent effect on the adsorption spectrum of VO(acac)2. Taken from ref 58, based on the NMR chemical shift of triethylphosphine oxide in the respective pure solvent. Taken from ref 61, based on the solvatochromic shift of a pyridinium-A-phenoxide betaine dye. 

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. 

Solvatochromic shifts are rationalized with the aid of the Franck-Condon principle, which states that during the electronic transition the nuclei are essentially immobile because of their relatively great masses. The solvation shell about the solute molecule minimizes the total energy of the ground state by means of dipole-dipole, dipole-induced dipole, and dispersion forces. Upon transition to the excited state, the solute has a different electronic configuration, yet it is still surrounded by a solvation shell optimized for the ground state. There are two possibilities to consider ... 

The dielectric constant and refractive index parameters and different functions of them that describe the reactive field of solvent [45] are insufficient to characterize the solute-solvent interactions. For this reason, some empirical scales of solvent polarity based on either kinetic or spectroscopic measurements have been introduced [46,47]. The solvatochromic classification of solvents is based on spectroscopic measurements. The solvatochromic parameters refer to the properties of a molecule when its nearest neighbors are identical with itself, and they are average values for a number of select solutes and somewhat independent of solute identity. 

Small molecule size-c Ecluslon chrmutography 441 Soap-film meter (GC) 4, 235 Solid-phase extraction 777 cartridges 777 membranes 780 optimization 777, 783 sorbents 778, 785 trace enrichment 777, 783 Solubility parameters 460 Solvatochromic parameters GC 191... 

A question which has intrigued colour chemists for years is why indigo, a relatively small molecule, absorbs at such long wavelengths. The colour of indigo depends crucially on its environment. It is known that, in the vapour phase, the only situation in which it approaches a monomolecular state, indigo is red. In solution, indigo exhibits pronounced positive solvatochromism in non-polar solvents it is violet, while in polar solvents it is blue. In the solid state, and when applied to fabric as a vat dye, it is... 

Tables 11-6, 11-7, and 11-8 show calculated solvatochromic shifts for the nucle-obases. Solvation effects on uracil have been studied theoretically in the past using both explicit and implicit models [92, 94, 130, 149, 211-214] (see Table 11-6). Initial studies used clusters of uracil with a few water molecules. Marian et al. [130] calculated excited states of uracil and uracil-water clusters with two, four and six water molecules. Shukla and Lesczynski [122] studied uracil with three water molecules using CIS to calculate excitation energies. Improta et al. [213] used a cluster of four water molecules embedded into a PCM and TDDFT calculations to study the solvatochromic shifts on the absorption and emission of uracil and thymine. Zazza et al. [211] used the perturbed matrix method (PMM) in combination with TDDFT and CCSD to calculate the solvatochromic shifts. The shift for the Si state ranges between (+0.21) - (+0.54) eV and the shift for the S2 is calculated to be between (-0.07) - (-0.19) eV. Thymine shows very similar solvatochromic shifts as seen in Table 11-6 [92],...

Solvatochromic shifts for cytosine have also been calculated with a variety of methods (see Table 11-7). Shukla and Lesczynski [215] studied clusters of cytosine and three water molecules with CIS and TDDFT methods to obtain solvatochromic shifts. More sophisticated calculations have appeared recently. Valiev and Kowalski used a coupled cluster and classical molecular dynamics approach to calculate the solvatochromic shifts of the excited states of cytosine in the native DNA environment. Blancafort and coworkers [216] used a CASPT2 approach combined with the conductor version of the polarizable continuous (CPCM) model. All of these methods predict that the first three excited states are blue-shifted. S i, which is a nn state, is blue-shifted by 0.1-0.2 eV in water and 0.25 eV in native DNA. S2 and S3 are both rnt states and, as expected, the shift is bigger, 0.4-0.6eV for S2 and 0.3-0.8 eV for S3. S2 is predicted to be blue-shifted by 0.54 eV in native DNA. 

There have been several other attempts to define solvent polarity parameters, among the more successful being those related to solvatochromic shifts the shift in wave-length/frequency of a band in the spectrum of a suitable absorbing species resulting from its interaction with the molecules of a series of different solvents. Particularly large shifts were observed with the zwitterion (51),... 

It is possible, however, that the electrochromic response of some styrylpyridi-nium probes, for example, RH421 (see Fig. 2), is enhanced by a reorientation of the dye molecule as a whole within the membrane. There is a steep gradient in polarity on going from the aqueous environment across the lipid headgroup region and into the hydrocarbon interior of a lipid membrane. Therefore, any small reorientation of a probe within the membrane is likely to lead to a change in its local polarity and hence a solvatochromic shift of its fluorescence excitation spectrum. Such a... 

Table I lists a variety of organic nonlinear materials which have appeared in the literature their relative powder efficiencies, absorption cutoffs and /3 values (if available) are also provided. These materials are "typical" only in that they represent results from the few classes of organic compounds investigated to date, yet they are instructive in that one learns which molecular properties may be important. A few caveats are in order to avoid misinterpretation of the data in Table I. Except for compound 10 (19) all the powder efficiency and cutoff data are from our own measurements. Powder measurements were performed on ungraded samples using the Nd YAG output at 1.06/t as fundamental since powder efficiency is a function of particle size distribution and a variety of other factors (3) these values are only semiquantitative. The cutoff values are the wavelengths for which 10-4M solutions in ethanol (unless otherwise indicated) have no absorbance. The cutoff values will be similar to those found in crystal state except where intermolecular charge transfer is important in the crystal or the molecule is solvatochromic, this latter effect being quite common for cyanine dyes such as...

The details of how nitroaromatic explosive molecules interact with the chromo-phores in the polymer matrix requires further study. Initial observations suggest that because nitroaromatic explosive molecules are highly electron-deficient, that chro-mophores have an electron-rich donor and bridge, and that both nitroaromatic explosives and chromophores are highly polar, explosive molecules and chromo-phores have a strong tendency to interact with each other. The interaction between explosives and the polymer takes place in two steps. In the initial step nitroaromatic explosive molecules create a more polar environment around the chromophores. The increased polar environment produces a solvatochromic red-shift of the... 

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