Polarity/polarizability solvatochromic probes

Bosch, Roses and coworkers explored the use of solvatochromic probes in solvent mixtures involving various alcohols with water as well as with other alcohols, hexane and benzene in a series of papers106-110. The aniline derivatives they employed were 5 for the polarity/polarizability and the 8/5 probe pair for the EPD/HBA properties of the mixtures, in conjunction with other suitable non-aniline probes. In order to ensure that what is being... 

Aniline derivatives have also been employed as solvatochromic probes to characterize the solvation abilities of various polymers and polymer surfaces. Thin films of various polymers were prepared by Paley and coworkers171 that incorporated the probe 7 for studying the polarity/polarizability and the probe pair 8/7 for studying the HBA/EPD... 

A brief review has been presented of the correlation analysis of solvolysis rates 50 years later, i.e. since Grunwald and Winstein proposed their eponymous equation in 1948.111 -pije authors then propose a method of correlation analysis involving multiple regression on solvent scales SPP (polarity-polarizability), SA (acidity) and SB (basicity). These scales are based on the solvatochromism of suitable probes and were initially for pure (i.e. one-component) solvents, but have now been extended to binary solvent mixtures. This enabled the authors to present a correlation for the solvolysis rate constants of r-butyl chloride in 27 pure solvents and 147 binary solvent mixtures, having a correlation coefficient r = 0.990 and a standard error of the estimate s = 0.40. The most important term in the equation is that involving SPP next comes... 

The Lewis basicity or HB A ability of solvents is described by the Kamlet-Taft parameter, measured by means of the couples of solvatochromic probes 4-nitrophenol compared to 4-nitroanisole or 4-nitroaniline compared to 4-nitro-N, N-diethyaniline, the second probe of the couple serving to eliminate the effects of the solvent polarity and polarizability on its first probe. The resulting values of from the compilation of Jessop et al. [410], supplemented with data from Spange etal. [416] are shown inTable 6.16. An alternative measure of this property that has been applied by Schade et al. [413] to RTILs is Catalan s SB parameter, using the solvatochromic probe N.N-dimethyl-4-aminobenzodifuranone, and the resulting values are shown in Table 6.16. The SB values are linear with the values SB = 0.126 +1.056/. The basicity decreases in a series of RTILs with a common anion phosphonium > ammonium > pyrrolidinium > pyridinium > imidazolium, but more moderately than the acidity increases in the opposite direction shown above as shown by Spange et al. [416]. 

The polarizability of solvents, combined with their polarity, are measured by the Kamlet-Taft n values, obtained most profitably with the solvatochromic probe 4-nitroanisole and shown, as compiled by Jessop et al. [410] and supplemented with values from Kochly et al. [414] and Spange et al. [416] in Table 6.16. The jt values are in a narrow range, 0.95 0.15, i.e., the RTILs are all very polar as expected for ionic liquids. The disadvantage of having both these properties in raie parameter is removed by the separate Catalan parameters SP for polarizability and SdP for dipolarity. These use results from two solvatochromic probes a thiazoline one and 2-(4-(N,N-dimethylamino)benzylidene)malononitrile according to Schade et al. [413], and the values of SP and SdP are also shown in Table 6.16. The polarizability of RTILs is not affected much by the acidity or basicity of its constituent ions, but their polarity does depend on these properties. 

Of the existing solvent scales, the Kamlet and Taft n scale ( D appears appropriate for use with supercritical fluid solvents. The basis of the Kamlet and Taft scale is the effect of solvent polarity and polarizability on the energy of the n - it electronic transition of a solute probe molecule. Solvent molecules in proximity to a solute (the cybotatic region) differentially affect the electronic energy levels of solutes (the solvatochromic effect)... 

Catalan (1995) has developed a set of polarity parameters known as the solvent bipolarity-polarizability (SPP) scale. Like the tt scales, the SPP parameters are based on the abihty of the solvent to shift the positions of absorption bands in a test molecule used as a probe. The effect, known as solvatochromism, utilizes 2-(N,Af-dimethylamino)-7-nitrofluorene (DMANF) by measuring the shift in the absorption spectrum as a series of solvents is used. The value of SPP for each solvent is calculated from the relationship... 

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