Solvatochromism, theory

Sodium nitrite, in monomethine thiazolo-cyanine synthesis, 52 Solvatochromism, of neutrocyanines, 75 of selenazole dyes. 251 Solvent, effect in resonance theory, 71 polarity of, in relation with solvatochromism. 75... 

There are single- and multiparameter approaches for determining the polarity and separation of contribution of different interactions to the total effect of polarity on spectroscopic characteristics. They are based on different theories of solvatochromic shifts of absorption and fluorescence bands. 

The assumptions made in theories of solvatochromic shifts, together with the uncertainty over the size and shape of the cavity radius, explain why the determination of excited-state dipole moments is not accurate. Examples of values of excited state dipole moments are given in Table 7.3. 

Solvatochromic Shifts of Ions. There is at the present time no theory of the solvatochromic shifts of ions except for the effect of the change of volume in different electronic states. This follows from the Born equation, and a being the ionic radii in states i and f (initial and final). 

This external or outer-sphere parameter A0 can be expressed according to a modified form of the Born equation to take into account only the solvent s orientation polarization. (As in the theory of solvatochromic shifts, it is assumed that the induction polarization can follow electronic motion.)... 

Within the QM continuum solvation framework, as in the case of isolated molecules, it is practice to compute the excitation energies with two different approaches the state-specific (SS) method and the linear-response (LR) method. The former has a long tradition [10-24], starting from the pioneering paper by Yomosa in 1974 [10], and it is related to the classical theory of solvatochromic effects the latter has been introduced few years ago in connection with the development of the LR theory for continuum solvation models [25-31],... 

R. Cammi and J. Tomasi, Nonequilibrium solvation theory for the polarizable continuum model - a new formulation at the SCF level with application to the case of the frequency-dependent linear electric-response function, Int. J. Quantum Chem., (1995) 465-74 B. Mennucci, R. Cammi and J. Tomasi, Excited states and solvatochromic shifts within a nonequilibrium solvation approach A new formulation of the integral equation formalism method at the self-consistent field, configuration interaction, and multiconfiguration self-consistent field level, J. Chem. Phys., 109 (1998) 2798-807 R. Cammi, L. Frediani, B. Mennucci, J. Tomasi, K. Ruud and K. V. Mikkelsen, A second-order, quadratically... 

J. Jeon and H. J. Kim, A continuum theory of solvation in quadrupolar solvents. I. Formulation, J. Chem. Phys., 119 (2003) 8606-25 J. Jeon and H. J. Kim, A continuum theory of solvation in quadrupolar solvents. II. Solvation free energetics, dynamics, and solvatochromism, J. Chem. Phys., 119 (2003) 8626-35. 

In asymmetric complexes of the type [(bpy)2RuCl(pi-pyz)Ru-(NH3)4L]4+, studies (94) revealed that there is a solvent donor-number (DN)-dependent contribution to the Frank-Condon barrier of approximately 0.006 eV/DN, which completely overwhelms the dielectric-continuum-theory-derived (l/Dop-l/Ds) solvent dependence typically observed in symmetrical dimers. In this case, variations in MMCT Eop with solvent give linear correlations when plotted against solvent dependent AEm, the difference in potential between the two ruthenium(III/II) couples, as shown in Fig. 10. The microscopic origin of this solvent effect was described by Curtis, Sullivan, and Meyer (122) in their study of solvatochromism in the charge transfer transitions of mononuclear Ru(II) and Ru(III) ammine complexes. The dependence... 

According to the McRae-Bayliss model of solvatochromism [69, 70] which is directly evolved from Onsager s reaction field theory [80], the electronic transition from ground [g) to excited state (e) of a solvatochromic solute is given by Eq. (6-1) [318] ... 

A rational strategy in identifying structural parameters appropriate for QSRR analysis should start from the accepted theories of chromatographic separations. These structural parameters obtained. should quantify the abilities of analytes to take part in the postulated intermolecular interactions which determine chromatographic. separations. Empirical or semi-empirical structural parameters of analytes based on the solvatochromic comparison method and on the linear solvation energy relationships (LSER) belong to that categoiy of structural descriptors. 19,40). 

The degree of clustering may be determined by a direct comparison of the experimental value of the solvatochromic parameter, for example. Ex, with the value which is calculated for a honx)geneous polarizable dielectric. Diis calculation has been done using the McRae-Bayliss nKxlel(221 which is based on the continuum reaction field theory of Onsager. 

This clustering theory may be tested using solvatochromic data. By assuming a linear relation between V2 and kx, in accordance with experimental iesults(6.25). an important result is obtained... 

Figure 6. Qustering of CHFj about (dimethylamino)benzonitrile at 50 C based on solvatochromic shifts in fluorescence (A data from ref. 26, — Onsager reaction field theory).

Kauffman and coworkers118 119 tried to fit the solvatochromic shifts of l-(9-anthryl)-3-(4-/V,/V-dimcthylanilino)propanc (83), relative to the hydrocarbon homomorph with the dimethylamino group replaced by H, to the dielectric non-ideality of solvent mixtures involving hexane with ethanol, tetrahydrofuran and dichloromethane. The shifts were not linear with the mole fraction of the polar component, and Suppan s theory of dielectric enrichment was applied to the data. It was found that the dielectric enrichment that can be calculated from the relative permittivities of the components and of the mixtures is not sufficient to account for the observed solvatochromic shifts, but that preferential solvation of the probe by the polar component is superimposed on this dielectric effect. Earlier,... 

The two parts of the present volume consist of 17 chapters written by experts from 10 countries. They start with historical background, followed by chapters on the theory, structure, thermochemistry, photophysics and photochemistry and electrochemistry of anilines, on their mass spectrometry, NMR spectra and analysis and on their modern syntheses by transition metal catalysed processes. Other chapters deal with their rearrangements, their reactivity as nucleophiles, their use as solvatochromic probes, their hydrogen bonded complexes, and their versatile uses in the chemical industry, and the relevant topic of toxicity and environmental aspects. A chapter on a special group of anilines—the proton sponges—ends the book. 

---