Ethyl solvatochromism

The dramatic influence of solvent effects on the UV and visible spectra of certain pyridine compounds, known generally as a solvatochromic effect, has been much utilized in the expression of solvents effects. The polarity parameter. Z or ET is defined (58JA3253, B-68MI204002) from the longest wavelength charge transfer band of 1-ethyl-4-methoxycar-bonylpyridinium iodide (equation 3). 

Solvent polarity parameters — use solvatochromic dyes (dyes whose electronic transitions are strongly dependent on the nature of the solvent) as indicators of solvent polarity. A comprehensive solvent polarity scale was first proposed by Kosower who defined the polarity parameter, Z, as the molar transition energy, Ej, for the charge transfer band of 1-ethyl-(methoxycarbonyl)pyridynium iodide in a given solvent as... 

A striking example is the negatively solvatochromic effect observed for l-ethyl-4-(methoxycarbonyl)pyridinium iodide, the UV/Vis spectra of which in a variety of solvents are shown in Fig. 6-3 [65-67]. The longest-wavelength band of the ground-state ion-... 

Kosower [5, 55] has taken the longest-wavelength intermolecular charge-transfer (CT) transition of l-ethyl-4-(methoxycarbonyl)pyridinium iodide as a model process. It exhibits a marked negative solvatochromism cf. the formula of this dye and its UV/Vis... 

The same authors also introduced a r scale of solvent dipolarity/polarizability [84a]. This n scale is so named because it is derived from solvent effects on the n n electronic transitions of a selection of seven positively solvatochromic nitroaromatics of the type D-C6H4-A, where D and A stand for electron-donor e.g. NMe2) and electron-acceptor e.g. NO2) groups, respectively 4-nitroanisole, A,A-diethyl-3-nitroaniline, 4-methoxy-/ -nitrostyrene, 1-ethyl-4-nitrobenzene, A-methyl-2-nitro-p-toluidine, N,N-diethyl-4-nitroaniline, and 4-(dimethylamino)benzophenone. Given a solvatochromic indicator compound, the n value for a solvent S was defined according to Eq. (7-32) ... 

Af-Butyl-4-nitroaniline (30) was also shown42 to be able to donate a hydrogen bond to HBA solvents, hence could be used as a solvatochromic probe, but has not been explored further in this respect. Drago29 reported the wavenumbers of the lowest energy absorption bands of three /V-alkyl-substituted nitroanilines 27, /V-ethyl-4-nitroanilinc (31) and N-ethyl-3-nitroaniline (32). Their spectral shifts relative to that in dioxane are shown in Figure 2 as a function of / Kt and a fair correlation is seen. 

Amine-substituted benzimidazole was studied with regards to its emission spectra in various solvents71. The spectral shifts of l-methyl-6-aminobenzimidazole (65a) from ethyl acetate (peak at 330 nm) to pyridine (peak at 470 nm) are appreciable, but there appears to be no systematic dependence on the polarity or HBA/EPD properties the peak emissions are at 370 nm for hexane and 362 nm for formic acid, and in many solvents 65a emits at 354 nm. Substitution of V-p-tolyl instead of the amino group at the 6 position (65b) did not improve the solvatochromic performance. 

Another attempt to relate the results from the use of a solvatochromic probe (Phenol Blue (66)) to the inherent properties of solvent mixtures was made by Phillips and Brennecke122. They obtained the interaction energies (required for the application of the non-random two-liquid (NRTL) approach) of 66 with each of the solvent components from its solubility in the neat solvent. The mixtures studied contained cyclohexane as one component and acetone, triethylamine, ethyl butyrate, cyclohexanone, toluene and acetophenone as the other. Then the local compositions deduced from the solvatochromism of 66 were compared with those calculated by the NRTL equation and reasonable agreement was found. 

Wetzler and coworkers123 employed 4-aminophthalimide (63) and 4-amino-lV-methyl-phthalimide (64) as solvatochromic (and thermochromic) fluorescent probes in solvent mixtures. A bathochromic shift of the emission spectra was found in mixtures of toluene with ethanol and with acetonitrile123 when the more polar solvent was added to toluene, but raising the temperature causes a relative hypsochromic effect. Mixtures of benzene and acetonitrile were studied by Nevecna and coworkers124 for their polarity by means of the probes 46 and 47 and with respect to the correlation of this with the rate constants of the reaction of triethylamine with ethyl iodide. The fluorescence of the ammonium salt of 4-(l-naphthylsulfonate)aniline (84) in dioxane and water mixtures was studied by Hiittenhain and Balzer125. 

Mancini PME, Adam C, del Perez AC, Vottero LR (2000) Solvatochromic and kinetic response models in (ethyl acetate + chloroform or methanol) solvent mixtures. Molecules 5 587-588... 

The indicators whose solvatochromic behavior was analyzed in terms of Equation 42 were ethyl 4-aminobenzoate (9), 4-aminobenzophenone (10), 3,5-dinitroaniline (II), 3-nitroaniline (12), and N-ethyl-3-nitroaniline (13). Because, with amphiprotic HBA-HBD solvents, these indicators form type-AB... 

The Z scale is based on the strong solvatochromism of the l-ethyl-4-(methoxycarbonyl)pyridinium iodide ion-pair (4) and defined by the position (in kcal mol ) of the maximum of its first absorption band, which has marked intermolecular charge-transfer connotations according to Scheme IV (the excited state of the chromophore is much less... 

Amino-5-ethyl-oxido-6-phenylphenanlhridinium betaine was shown recently by Finkentey and Zimmermann [Fi81] to be a new solvatochromic compound. Its structure was proved by H-NMR and mass spectroscopy. In aqueous solutions it is in a pH dependent equilibrium with its conjugated aminophenol and the twice protonated dication. The betaine shows a strong negative solvent effect. Its solutions in aprotic solvents are blue, in amphiprotic solvents red to purple. 

MPI24 is a structural analogue of l-ethyl-4-carboethoxypyridinium iodide (EPI) (SCHEME I) i.e., of the compound originally proposed by Kosower23 for semiempirical measurement of the solvent polarity. Very similar wavelengths were found for the maxima of the solvatochromic bands of these compounds. The polarity scale based on MPI may, therefore, be correlated with a similar scale proposed by Dimroth.25... 

Figure 2. Correlation of a semiempirieal polarity scale (Ep (IB DNS)), based on the shift of the solvatochromic emission band of the compound EB DNS, with the Dimroth parameter 730 For symbols of the solvents see Figure 1 (24) ethylene glycol, (25) ethyl cellosolve. EpdN DNS) (kJ/mol) is the energy of the emission maximum of DNS fluorochrome E -gQ (kcal/mol).

In ethyl acetate/methanol, with methanol content over 2.5 vol. %, the wavelength of the solvatochromic maximum of merocyanine bound to... 

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