Solvatochromic method

Another UV/Vis spectroscopic method for the determination of water in organic solvents involves the use of solvatochromic dyes (such as the pyridinium A-phenolate betaine dye (44) m Chapter 7.4), and is based on the observation that water has a very high polarity compared with most organic solvents [142-145]. Even small amounts of water cause a strong hypsochromic band shift of the dissolved solvatochromic dye, which can be related to the water content by a cahbration curve. A typical detection hmit of this method is of the order of 1 mg water in 1 mL solvent for routine spectrophotometers [142], An analogous solvatochromic method has been developed for the determination of aqueous ethanol mixtures [146],... 

The solvatochromic method developed by Taft and coworkers [94] has also been used to explain the solvent effect on redox potentials. Lay [95] considered specific hydrogen bonding contributions to the thermodynamics and kinetics of electron transfer. 

The understanding and reliable prediction of the influence of the solute-solvent interactions on the nonlinear optical properties of molecular systems is a significant issue for a width range of theoretical and experimental areas of studies. In this review, it was shown that the simple two-state approximations combined with tlie solvatochromic methods are an effective tools in prediction tlie direction of tlie changes of molecular nonlinear responses as a function of solvent polarity. This methodology based on the description of the solvent effects at the molecular level should be treated as a supporting for the most sophisticated quantum chemical approaches. 

Bartkowiak reviewed the connection between the NLO response and solva-tochromlc behavior of donor-acceptor Tr-conjugated molecules. The marked NLO properties of these molecules are associated with an intra-molecular charge-transfer excited state. This author points out that the environmental interactions may have a very significant effect on the hyperpolarizabilities (they may even lead to a change of sign). Bartkowiak shows that a simple two-state model combined with the solvatochromic methods may allow the prediction of changes of in molecular hyperpolarizabilities as a function of the solvent polarity. 

To investigate the possibility of variable ESA, we have used the solvatochromic method of Kamlet and co-workers (7-10). According to this approach, a solvent-dependent phenomenon (in this case log solvolysis rate k) is a function of four solvent properties solvent hydrogen-bond donor ability or electrophilicity, a solvent hydrogen-bond acceptor ability or nu-... 

The solvatochromic methods (solvent-shift methods) are experimentally much simpler as they do not use any external field. However, they are less reliable because of the numerous... 

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. 

The precision of the solvatochromic method was further tested against the association constants AT/, between phenol (5a) and a variety of HBA bases in CCI4 as determined by Gramstad and co-workers (75). As in the case of p-flu-orophenol, a good linear relationship was found to exist between log Kf and the enhanced solvatochromic shifts ... 

Since the two level model (Eq. 4) applies well to NLO chromophores characterized by a major CT transition, the solvatochromic method may afford a way to evaluate the quadratic hyperpolarizability, but only the component along the major CT direction, by recording electronic absorption spectra of this absorption... 

The shift in the n —> rt band is largely caused by solvent acidity however, an n — jr transition is also obviously sensitive to the polarity of the medium, the contribution of which must be subtracted if acidity is to be accurately determined. To this end, our group used the solvatochromic method of Kamlet and Taft to plot the frequency of the absorption maximum for the n —> n transition against solvent polarity (the SPP value). As expected, non-acidic solvents exhibited a linear dependence [eq. (10.3.13)], whereas acidic solvents departed from this behavior -die more acidic the greater the divergence. This departure from the linear behavior described by eq. [10.3.13] is quantified by Avdetz>... 

The solvatochromic method employs an indicator substance as a probe at a low concentration, which is used as a stand-in for the ions or other solute molecules to be... 

The most informative approach to understanding these solvation forces at the present time is the Solvatochromic method introduced by Kamlet and his colleagues, which separates the contributions to log/ into measures of solute size, polarity/polarizability, and hydrogen bond donor and acceptor strength. In its most general form, log/ for any solvent pair can be stated as... 

The shift in the n u band is largely caused by solvent acidity however, an n 71 transition is also obviously serrsitive to the polarity of the mediitm, the contribution of which must be subtracted if acidity is to be accttrately determined. To this end, oiu group used the solvatochromic method of Kamlet and Taft to plot the frequency of the... 

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