Solvatochromic method, application

A statistical evaluation and comparison of solvatochromic methods used to determine excited-state dipole moments has been carried out by Koutek [167]. Solvent effects can be taken into consideration using the reaction field theory developed by Katritzky, Zemer, Szafran, and Karelson [176-179] and Siretskii, Kirillov, and Bakhshiev [180] have proposed an equation containing a cos where is the angle between the direction of the ground-state dipole moment and the excited-state dipole moment. The equation worked well for certain aromatic dyes but its general applicability has not been tested. 

An example of an application is shown in Fig. 30.10. This concerns the classification of 42 solvents based on three solvatochromic parameters (parameters that describe the interaction of the solvents with solutes) [13]. Different methods were applied, among which was the average linkage method, the result of which is shown in the figure. According to the method applied, several clusterings can be found. For instance, the first cluster to split off from the majority of solvents consists of solvents 36, 37, 38, 39, 40, 41, 42 (t-butanol, isopropanol, n-butanol. 

Application of the solvatochromic comparison method (Kamlet and coworkers80) reveals a competition between intermolecular and intramolecular hydrogen bonding in molecules bearing both donor and acceptor groups81 such as 17. 

Owing to the original determination from uv—vis spectral solvatochromic shifts, 7T, B, and QLm are called solvatochromic parameters. General rules for estimation of these variables have been proposed (258). Examples of individual parameter investigations are available (260,261). As previously mentioned, individual LFER—LSER studies are performed on related materials. A common method to link these individual studies to group contribution methods, and thereby expand the applicability, is by expansion of solvatochromic parameters to log—linear relationships, such as... 

A sampling of applications of Kamlet-Taft LSERs include the following. (/) The Solvatochromic Parameters for Activity Coefficient Estimation (SPACE) method for infinite dilution activity coefficients where improved predictions over UNIFAC for a database of 1879 critically evaluated experimental data points has been claimed (263). (2) Observation of inverse linear relationship between log 1-octanol—water partition coefficient and liquid... 

Three other methods are applicable in certain circumstances, particularly if there is prior experience in their use. These are the connectivity, solvatochromic, and UNIFAC methods. 

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... 

The p scale was proposed to measure solvent hydrogen bond basicity, i.e. the ability of a bulk solvent to act as hydrogen bond acceptor. This scale was derived by systematic application of the solvatochromic comparison method the final p values were calculated by averaging 13 p parameters for each solvent obtained with different solutes and different physicochemical properties [Kamlet et al, 1981a Kamlet et al, 1983]. 

The development of chiro-solvatochromic compounds should lead to interesting applications. These probes should be capable of distinguishing pairs of enantiomers, as a result of stereoselective interactions, giving rise lo significant spectra differences between solutions of the diastereomeric complexes. One may envisage simple and fast methods for the determination of the enantiomeric... 

The initial construction of this scale involved the systematic application of the solvatochromic comparison method (72). Documentation of solvent-solute hydrogen bonding interactions by this method requires that three important... 

In this chapter, we concentrate on luminescence approaches that are most suitable for stilbenes to be molecular probes and are based on specific and nonspecific labeling, competition, solvatochromism, experimental molecular dynamics, and singlet-singlet and triplet-triplet energy transfer. A general survey is made of the physical principles and application of the fluorescence probe methods stressing on latest developments in this area. 

McRae s equation, which uses the Onsager dielectric functions, has been used to interpret the solvatochromism of a number of coordination compounds. Meyer and one of us have also used Kirkwood s approach, which is simpler since it neglects dispersion forces. Lippert s method is used for species in which absorption and emission data are available for the same excited state when the difference between absorption and emission energies is known a number of terms in the equations will cancel, and it is then relatively simple to obtain the ground- and excited-state dipole moments. This method is not usually applicable for coordination complexes as, if emission is observed, the emitting state is usually different from the main absorption band, e.g., in many cases absorption is to a singlet state and emission is from the corresponding triplet. 

That what follows is not intended just to give a complete overview of existing ideas, but to filter seminal conceptions and to take up more fundamental ideas. It should be mentioned that solvent relaxation phenomena, i.e., dynamic solvent effects, are omitted On the other hand, recent investigations of thermochromism and solvatochromism in solution have also been considered as a rapidly expanding field applicable to both, easy characterization of solvent properties as well as in technological applications. Such methods can be used to investigate mutual solute-solvent and solvent-solvent interactions for example in case of ions in solutions as well as in ionic liquids. 

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