Polymer Molecular Weight-Dependent Unusual Fluorescence Probe Behavior within 1-Butyl-3-methylimidazolium Hexafluorophosphate + Poly(ethylene glycol)

Abstract

Poly(ethylene glycols) (PEGs) and room-temperature ionic liquids (ILs) are both projected as possible alternatives to volatile organic compounds (VOCs). Their potential usage in chemical applications, however, is often hampered by their limited and, in some cases, undesired individual physicochemical properties. Properties of mixtures of PEG with a common IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) are assessed via responses of three fluorescence probes: pyrene (Py) and pyrene-1-carboxaldehyde (PyCHO) are the dipolarity sensing probes and 1,3-bis-(1-pyrenyl) propane (BPP) is the probe for microfluidity. All three probes demonstrate anomalous fluorescence behavior within the mixture of [bmim][PF6] with four different PEGs of average molecular weight (MW) 200, 400, 600, and 1500 g.mol(-1), respectively, across complete composition range. Cybotactic region dipolarity of the probe Py within the mixtures is observed to be higher than that expected from ideal additive behavior. PyCHO lowest energy fluorescence maxima implying the static dielectric constant around the cybotactic region shows values within the mixtures to be even higher than that in neat PEG, the component having higher static dielectric constant of the two, clearly indicating the milieu to have anomalously high dipolarity. "Hyperpolarity" inherent to the PEG+[bmim][PF6] mixture is confirmed. Intramolecular excimer-to-monomer fluorescence intensity ratio of BPP indicates the microfluidity within the mixture to be even lower than that within neat [bmim][PF6], the component with lowest microfluidity. Presence of strong solvent-solvent interactions within the mixture is proposed to be the major reason for the anomalous fluorescence probe responses. Specifically, extensive hydrogen-bonded network involving termini hydroxyls of PEGs and PF6- as well as ethoxy/hydroxyl oxygens of PEGs and the C2-H of bmim+ is proposed to be responsible for the unusual outcomes. Fluorescence probe responses are shown to be adequately predicted by a four-parameter simplified combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) model. Unusually altered physicochemical properties are demonstrated to be the key feature of the "hybrid green" PEG+IL systems.

Liquid mixtures of ionic liquids and polymers as solvent systems

“…On the contrary, the hydrogen bond basicity (ˇ) of the mixtures was found to lie below the ideal additive prediction. Anomalous "hyperpolarity" inherent to the PEG + [C 4 mim][PF 6 ] systems was confirmed by fluorescence probe behavior in an analogous work [66]. Tentatively, the authors explained the unusually enhanced properties in terms of an extensive network of hydrogen bond donors and acceptors, involving the C2 position of the imidazolium ring as donor and the terminal hydroxyl groups as well as the ethoxy groups of PEG as acceptors, and the [PF 6 ] − anion as acceptor and the terminal hydroxyl groups of PEG as donors.…”

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).…”

“…18,19,23,62 In order to distinguish the classical excimer, which forms in and exists only in the excited state, from the related species formed from interor intramolecular association of pyrene species before optical excitation, fluorescence excitation scans with emission wavelengths at 378 (monomer emission maximum) and 487 nm (excimer emission maximum), respectively, for 1Py(3)1Py were acquired. These two excitation scans of 1Py (3) 6 ], respectively, at each temperature investigated were found to be identical within our measurement precision.…”

Linking Diffusion–Viscosity Decoupling and Jump Dynamics in a Hydroxyl‐Functionalized Ionic Liquid: Realization of Microheterogeneous Nature of the Medium

“…[68] Moreover,t he polar domains are thought to be compact, as they are formed due to coulombic interactions betweenc ations and anions, whereas the nonpolard omains are rather loose,a nd are formed mainly by hydrophobic interactions amongt he alkyl groups. [68][69][70][71][72] BPP is aw ell-documented fluorescent probe that can be employed to detect microviscosity by measuring the excimer emission band, which is located in the 450-500 nm region, in its emission spectralp rofile. [68] Since the anionic moiety is hydrophobic FAPi nb oth [OH-Emim] [FAP] and [Emim][FAP],i ti sr easonablet oa ssume that the hydrophobic domains of these ILs are created by FAPm oieties and the polar domainsb yt he cationic moiety.I nterestingly,T able 3 also showst hat the faster rotational relaxation component of C153 is almost constanta tr oom temperature in both ILs, whereas the values for the slower component change.…”