Unusual Solvatochromism within 1-Butyl-3-methylimidazolium Hexafluorophosphate + Poly(ethylene glycol) Mixtures

Abstract

Hybrid "green" solvent systems composed of room-temperature ionic liquids (ILs) and poly(ethylene glycols) (PEGs) may have enormous future potential. Solvatochromic absorbance probe behavior is used to assess the physicochemical properties of the mixture composed of IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) and PEG (average molecular weights of 200, 400, 600, and 1500) at ambient conditions. Lowest energy intramolecular charge-transfer absorbance maxima of a betaine dye, i.e., E(T)(N), indicates the dipolarity/polarizability and/or hydrogen-bond donating (HBD) acidity of the [bmim][PF 6] + PEG mixtures to be even higher than that of neat [bmim][PF(6)], the solution component with higher dipolarity/polarizability and/or HBD acidity. Dipolarity/polarizability (pi*) obtained separately from the electronic absorbance response of probe N, N-diethyl-4-nitroaniline shows a trend similar to E(T)(N ) thus confirming the unusually high dipolarity/polarizability of the [bmim][PF(6)] + PEG mixtures. Similar to E(T)(N ) and pi*, the HBD acidity (alpha) of [bmim][PF(6)] + PEG mixtures is also observed to be anomalously high. Contrary to what is observed for E(T)(N ), pi*, and alpha, the hydrogen-bond accepting (HBA) basicity (beta) of the [bmim][PF(6)] + PEG mixtures is observed to be lower than that predicted from ideal additive behavior indicating diminished HBA basicity of the mixture as compared to its neat components. A four-parameter simplified combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation is shown to satisfactorily predict the solvatochromic parameters within [bmim][PF(6)] + PEG mixtures. It is demonstrated that [bmim][PF(6)] + PEG mixtures possess physicochemical properties that are superior to those of either the neat IL or the neat PEG.

Intramolecular Excimer Formation Dynamics of 1,3-Bis-(1-pyrenyl)propane within 1-Butyl-3-methylimidazolium Hexafluorophosphate and Its Polyethylene Glycol Mixtures

“…The Journal of Physical Chemistry B Article appear to depend on the H-bonding network present within the medium involving C2−H of the imidazolium cation and oxygen of the termini hydroxyl and/or the ethoxy units of the PEG (H bonding involving the PF 6 anion of the ionic liquid and the termini hydrogen of the PEG hydroxyl group may also contribute) as proposed earlier;[17][18][19]30 the more the H-bonded network, the longer the decay time. Further, the H-bond donating acidity (α)17 and the dipolarity/polarizability (as revealed by the E T N and π* values 17 along with pyrene and pyrene-1-carboxaldehyde fluorescence responses 19 ) of the ([bmim][PF 6 ] + PEG) mixtures also show maximum values in the region slightly rich in [bmim][PF 6 ] (closer to the equimolar composition).…”

“…17−19 For example, the dipolarity/polarizability and the H-bond-donating (HBD) acidity of mixtures of PEGs of different average molecular weight (MW) with ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([brim][PF 6 ]) were found to be significantly higher (hyperpolarity) than those of pure [bmim] [PF 6 ] or PEG. 17,18 Similarly, the dynamic viscosity of certain ([bmim][PF 6 ] + PEG) mixtures mixture was found to be higher (hyper viscosity) than that of either of the components also exhibited rare "hyperviscosity". 30 These interesting and unusual properties of ([bmim] [PF 6 ] + PEG) mixtures may afford unconventional and hard-to-predict results in important chemical reactions and processes.…”

Liquid mixtures of ionic liquids and polymers as solvent systems

“…In a further step demonstrating the special character of the mixtures of IL and PEG, Sarkar et al [65] focused on PEGs of lower molecular weight, from 200 g/mol up to 1500 g/mol, which are perhaps of higher interest in our case given their liquid status at or near room temperature. They assessed the properties of mixtures of these PEGs with [C 4 mim][PF 6 ], over the whole compositional range, by studying the solvatochromic absorbance probe behavior.…”

Solvatochromic absorbance probe behavior within 1-butyl-3-methylimidazolium hexafluorophosphate+propylene carbonate: Preferential solvation or solvent–solvent interaction?

“…Among the approaches to enhance solute solubility within ILs and to modify physicochemical properties of ILs in desirable fashion, addition of cosolvent(s) or mixing two or more ILs appears both simple and effective [12][13][14][15][16][17][18]. Towards this end, we have previously reported our investigations on the effects of added water [12,13], ethanol [14], aqueous-ethanol [15], poly(ethylene glycol)s [19], and other ILs [16] on a common and popular IL 1-butyl-3-methylimidazolioum hexafluorophosphate ([bmim][PF 6 ]).…”

“…Interestingly, neat propylene carbonate shows negligible hydrogen-bond donating (HBD) acidity, hydrogen-bond accepting (HBA) basicity and dipolarity/polarizability of neat propylene carbonate are significant [23][24][25][26][27]. However, it is recently shown [28], by using temperature-dependent 19 6 ] and the mixture, respectively), providing a much favorable milieu for different reactions to occur [29]. Another aspect at the same mixture composition worth mentioning is that activation energy of neat [bmim][PF 6 ] is two times that of the mixture (37.9 and 18 kJ mol −1 , respectively) [29].…”