The solvatochromic behavior of 2,6‐dichloro‐4‐(2,4,6‐triphenyl‐1‐pyridinio)phenolate (WB) was studied by UV–visible spectrophotometry in 32 pure solvents, in binary mixtures of 1‐butanol–cyclohexane (BuOH–Cyhx), and of water with methanol, ethanol, 1‐propanol, 2‐butoxyethanol (2‐BE), acetonitrile, 1,4‐dioxane and THF. The solvent polarity, ET(33) in kcal mol−1, was calculated from the position of the longest‐wavelength intramolecular charge‐transfer absorption band of WB and the results were compared with those for 2,6‐diphenyl‐4‐(2,4,6‐triphenyl‐1‐pyridinio)phenolate [RB, ET(30)] and of 1‐methyl‐8‐oxyquinolinium betaine [QB, ET(QB)]. For pure solvents, ET(33) is a linear function of ET(30), with a slope of practically unity. Steric crowding from the two ortho phenyl rings of RB hinders the formation of H‐bonds with solvents, which results in similar susceptibilities of WB and RB to solvent acidity. For binary solvent mixtures, all plots of ET versus the mole fraction of 1‐butanol or water are non‐linear owing to preferential solvation of the probe by one component of the mixed solvent and, when applicable, to solvent micro‐heterogeneity. Preferential solvation due to non‐specific and specific probe–solvent interactions was calculated for BuOH–Cyhx and water–acetonitrile. Both solvation mechanisms contribute to the non‐ideal behavior in the former binary mixture, whereas probe–solvent specific interactions dominate the solvatochromic behavior in the latter. The composition of the probe solvation shell was calculated. In aqueous alcohols, preferential solvation is by the alcohol. In water–aprotic solvent mixtures, preferential solvation of RB and WB is by the solvent which is present in lower concentration, whereas QB seems to form its own, water‐rich solvation shell over a wide range of water concentration. Copyright © 2000 John Wiley & Sons, Ltd.
epoc ABSTRACT: Thermo-solvatochromism of 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)-phenolate, 1-methylquinolinium-8-olate and 4-[2-(1-methylpyridinium-4-yl)ethenyl]-phenolate, in the temperature ranges 10-45 C (methanol) and 10-60 C (1-and 2-propanol) was investigated in binary water-alcohol mixtures. Thermo-solvatochromic data were treated according to a modified model that explicitly considers the presence of 1:1 water-alcohol species in bulk solution, and its exchange reactions with water and alcohol in the solvation micro-sphere of the probe employed. Concentrations of these complex species were calculated from density data. Plots of the empirical solvent polarity parameter, E T , versus effective mole fraction of water in the binary mixtures indicate that the probes are preferentially solvated by the alcohol, except for one case. A temperature increase causes gradual desolvation of the probe, due to a decrease in the H-bonding abilities of all components of the binary solvent mixture.
The thermo‐solvatochromic behavior of 2,6‐dichloro‐4‐(2,4,6‐triphenylpyridinium‐1‐yl)phenolate (WB), 1‐methylquinolinium‐8‐olate (QB) and 4‐[2‐(1‐methylpyridinium‐4‐yl)ethenyl]phenolate (MC) was investigated in binary mixtures of water (W) and 2‐alkoxyethanols (ROEtOH) in the temperature ranges from 10 to 60°C (2‐ethoxyethanol and 2‐n‐propoxyethanol) and 10 to 40°C (2‐n‐butoxyethanol). Thermo‐solvatochromic data were treated according to a model that is based on the presence in bulk solution of three solvents, W, ROEtOH and a 1:1 H‐bonded species, ROEtOH–W. Solvation by ROEtOH–W is favored over solvation by either of the two precursor solvents. The present data, and those recently published on thermo‐solvatochromism of the same probes in five alcohols (methanol, ethanol, 1‐propanol, 2‐propanol and 2‐methyl‐2‐propanol) and one ROEtOH (2‐methoxyethanol), were submitted to regression analysis. The results indicate that solvation is more sensitive to solute–solvent hydrophobic interactions than H‐bonding between the probe phenoxy oxygen and the hydroxyl group of the H‐bond donating solvent (HBD). Temperature increase results in gradual desolvation of the probes, due to the concomitant decrease of the structure of all components of the binary solvent mixture. For pure solvents, the temperature‐induced desolvation depends on the structure of the probe (order: WB>MC>QB) and the HBD solvent (order: 2‐ethoxyethanols>aliphatic alcohols, for the same alkyl group; organic solvent>water). The probe solvatochromic response is due to the electronic transition zwitterion→di‐radical; it serves as a model for reactions that are associated with a large polarity difference between the reagents and activated complexes. For WB, for ΔT = 50°C, the desolvation energies range from 2.1 to 3.7 kcal mol−1. The contribution of temperature‐induced desolvation to the activation enthalpies of these reactions is, therefore, important. Copyright © 2005 John Wiley & Sons, Ltd.
The solvatochromic behavior of 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)-1-phenolate (RB), 2,6-dichloro-4-(2,4,6-triphenyl-1-pyridinio)-1-phenolate (WB), 1-methyl-8-oxyquinolinium betaine (QB), and sodium 1-methyl-8-oxyquinolinium betaine 5-sulfonate (QBS) has been studied as a function of increasing the length of R in the series C12H25N+R3Br- (R = methyl, ethyl, n-propyl, and n-butyl). The microscopic polarity of water at the solubilization site of the micelle-bound probe, E T in kcal/mol, has been calculated from the position of its intramolecular charge-transfer band in the UV−vis region. Calculated polarities depend on the length of R and the probe structure and charge. This is attributed to gradual “dehydration” of the interfacial region as a function of the increasing length of R, and different (average) solubilization sites of the probes. Thus, hydrophobic RB and WB are located in a less polar environment than hydrophilic QB and QBS. These conclusions have been confirmed by measuring 1H NMR chemical shifts of the discrete protons of both surfactant and probes. The “effective” water concentration at the probe solubilization site, [water]interfacial, has been calculated from solvatochromic data in bulk aqueous 1-propanol and aqueous 1,4-dioxane. Both reference binary mixtures gave consistent [water]interfacial; our data also agree with those based on the use of a micelle-bound arenediazonium ion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.