Thermo-solvatochromism of zwitterionic probes in aqueous alcohols: effects of the properties of the probe and the alcohol

Tada, Erika B.; Silva, Priscilla L.; Seoud, Omar A. El

doi:10.1039/b308550c

Cited by 28 publications

(53 citation statements)

References 55 publications

(14 reference statements)

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“…We treated the data obtained according to the following solvation model, employed in previous studies. [2][3][4] where (m) represents the number of solvent molecules whose exchange in the probe solvation shell affects E T (usually m Յ 2). Arguments for the use of 1:1 stoichiometry for Solv-W have been published elsewhere.…”

Section: Thermo-solvatochromism In Binary Solvent Mixturesmentioning

confidence: 99%

Thermo‐Solvatochromism of Merocyanine Polarity Probes – What Are the Consequences of Increasing Probe Lipophilicity through Annelation?

et al. 2008

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The question raised in the title has been answered by comparing the solvatochromism of two series of polarity probes, the lipophilicities of which were increased either by increasing the length of an alkyl group (R) attached to a fixed pyridine-based structure or through annelation (i.e., by fusing benzene rings onto a central pyridine-based structure). The following novel solvatochromic probes were synthesized:. The solvatochromic behavior of these probes, along with that of 2,6-dibromo-4-[(E)-2-(1-methylpyridinium-4-yl)ethenyl]phenolate (MePMBr 2 ) was analyzed in terms of increasing probe lipophilicity, through annelation. Values of the empirical solvent polarity scale [E T (MePMBr 2 )] in kcal mol -1 correlated linearly with E T (30), the corresponding values for the extensively employed probe 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (RB). On the other hand, the nonlinear correlations of E T (MeQMBr 2 ) or E T (MeAMBr 2 ) with E T (30) are described by second-order polynomials. Possible reasons for this behavior include: i) self-aggregation of the probe, ii) photoinduced cis/trans isomerization of the dye, and iii) probe structure-and solvent-dependent contributions of the quinonoid and zwitterionic limiting formulas to the ground and excited states of the probe. We show that mechanisms (i) and (ii) are not operative under the experimental conditions employed; experimental evidence (NMR) and theoretical calculations are presented to support the conjec-

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Section: Thermo-solvatochromism In Binary Solvent Mixturesmentioning

confidence: 99%

Thermo‐Solvatochromism of Merocyanine Polarity Probes – What Are the Consequences of Increasing Probe Lipophilicity through Annelation?

et al. 2008

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“…Briefly, whereas the ability of solvents to form hydrogen bonds with the phenolate oxygen of RB is attenuated due to steric hindrance by the two ortho phenyl rings, the corresponding ability of WB is enhanced because of lower steric hindrance around the phenolate oxygen, and the additional ability of two ortho chlorine atoms to form hydrogen bonds [39]. Additionally, our solvatochromic data have indicated that lipophilicity of both solvent and probe are important to solvatochromism [36,38,[40][41][42]; there is no provision for the latter property in eq. 3.…”

confidence: 99%

“…Figure 4 shows the dependence of E T (MePMBr 2 ) on χ W for mixtures of W with MeOH, 1-propanol, PrOH, MeCN, and dimethylsulfoxide (DMSO) at 25°C [45]. This dependence is not linear (i.e., it is not ideal); a large body of solvatochromic data shows that this is a general behavior [10,[13][14][15][16][37][38][39][40][41][42][43][44][45]. How can this dependence be explained?…”

confidence: 99%

“…The input data to calculate K dissoc include densities of the mixtures, the molar masses and volumes of the two components (V S and V W , respectively), along with initial estimates of K dissoc and V S-W . That is, K dissoc and V S-W are calculated simultaneously from the same set of experimental data [40][41][42][43]. This calculation, however, may be subject to uncertainty because both parameters (K dissoc and V S-W ) are correlated.…”

Section: Solvation In Binary Solvent Mixturementioning

confidence: 99%

“…3 [36][37][38][39][40][41][42][43][44][45]. Historically, the solvent polarity scales of RB and WB have been termed E T (30) and E T (33), respectively.…”

Section: Use Of Solvatochromic Dyes To Probe Solvationmentioning

confidence: 99%

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Solvation in pure and mixed solvents: Some recent developments

Seoud

2007

Pure and Applied Chemistry

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The effect of solvents on the spectra, absorption, or emission of substances is called solvatochromism; it is due to solute/solvent nonspecific and specific interactions, including dipole/dipole, dipole-induced/dipole, dispersion interactions, and hydrogen bonding. Thermo-solvatochromism refers to the effect of temperature on solvatochromism. The molecular structure of certain substances, polarity probes, make them particularly sensitive to these interactions; their solutions in different solvents have distinct and vivid colors. The study of both phenomena sheds light on the relative importance of the solvation mechanisms. This account focuses on recent developments in solvation in pure and binary solvent mixtures. The former has been quantitatively analyzed in terms of a multiparameter equation, modified to include the lipophilicity of the solvent. Solvation in binary solvent mixtures is complex because of the phenomenon of "preferential solvation" of the probe by one component of the mixture. A recently introduced solvent exchange model allows calculation of the composition of the probe solvation shell, relative to that of bulk medium. This model is based on the presence of the organic solvent (S), water (W), and a 1:1 hydrogen-bonded species (S-W). Solvation by the latter is more efficient than by its precursor solvents, due to probe/solvent hydrogen-bonding and hydrophobic interactions. Dimethylsulfoxide (DMSO) is an exception, because the strong DMSO/W interactions probably deactivate the latter species toward solvation. The relevance of the results obtained to kinetics of reactions is briefly discussed by addressing temperature-induced desolvation of the species involved (reactants and activated complexes) and the complex dependence of kinetic data (observed rate constants and activation parameters) in binary solvent mixtures on medium composition.

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