Influence of Chiral Ionic Liquids on Stereoselective Fluorescence Quenching by Photoinduced Electron Transfer in a Naproxen Dyad

Abstract

In a previous study of a naproxen dyad in a pair of N-methylimidazoliummethyl menthylether−NTf2 chiral ionic liquids (J. Phys. Chem. B 2008, 112, 7555), we observed that though intramolecular electron transfer was impeded, a consistent small stereodifferentiation in the fluorescence lifetime of the dyad was obtained. We proposed that this discrimination was purely electronic in nature and did not arise from geometrical effects, which can influence nonradiative rate processes, such as intramolecular electron transfer. In our present work, we have studied the interaction of the same chiral naproxen dyad molecule in both the previously studied menthyl-based NTf2 ionic liquids and also in bis(tertrabutylphosphonium) (TBP) d-,l-tartrate ionic liquids. Unlike in the menthyl-based IL pair, the amount of quenching is different in the bis(TBP) tartrate enantiomeric liquids and the tartrate enantiomers have a different temperature dependence on the nonradiative rate of the dyad. This chiral discrimination most likely arises from the steric effects of the different conformations of the chiral molecules. We have shown that the viscosity and polarity of the solvents can influence the rate of electron transfer. On the other hand, no such electron transfer quenching is observed in the menthyl-based NTf2 IL solvents. To our knowledge, this is the first example of chiral ionic liquids inducing a stereoselective fluorescence quenching by photoinduced, intramolecular electron transfer. In a previous study of a naproxen dyad in a pair of N-methylimidazoliummethyl menthylether-NTf 2 chiral ionic liquids (J. Phys. Chem. B 2008, 112, 7555), we observed that though intramolecular electron transfer was impeded, a consistent small stereodifferentiation in the fluorescence lifetime of the dyad was obtained. We proposed that this discrimination was purely electronic in nature and did not arise from geometrical effects, which can influence nonradiative rate processes, such as intramolecular electron transfer. In our present work, we have studied the interaction of the same chiral naproxen dyad molecule in both the previously studied menthyl-based NTf 2 ionic liquids and also in bis(tertrabutylphosphonium) (TBP) D-,L-tartrate ionic liquids. Unlike in the menthyl-based IL pair, the amount of quenching is different in the bis(TBP) tartrate enantiomeric liquids and the tartrate enantiomers have a different temperature dependence on the nonradiative rate of the dyad. This chiral discrimination most likely arises from the steric effects of the different conformations of the chiral molecules. We have shown that the viscosity and polarity of the solvents can influence the rate of electron transfer. On the other hand, no such electron transfer quenching is observed in the menthyl-based NTf 2 IL solvents. To our knowledge, this is the first example of chiral ionic liquids inducing a stereoselective fluorescence quenching by photoinduced, intramolecular electron transfer.

Configuration‐Dependent Photoinduced Electron Transfer in Diastereomeric Naphthalene‐Amino‐Naphthalene Triads

“…Specifically, diastereomeric NPX‐pyrrolidine dyads have attracted great attention in connection with stereoselective fluorescence quenching by EX or PET 3a. 4 These systems have proven to be appropriate models for the study of photophysical stereodifferentiation induced by chiral ionic liquids4a, b and for the investigation of singlet excited‐state quenching by means of spin chemistry methods 4d. e…”

Enhanced stability and activity of cellulase in an ionic liquid and the effect of pretreatment on cellulose hydrolysis

“…These difficulties have been overcome by the introduction of room temperature ionic liquids (ILs), which have been reported to dissolve substantial amounts of cellulose. ILs are novel compounds that have great potential for replacing conventional, volatile, environmentally harmful organic solvents used in many catalytic and organic reactions (Adhikary et al, 2008; Bose et al, 2009). Rogers and coworkers (Fort et al, 2007; Remsing et al, 2006; Swatloski et al, 2002) have carried out comprehensive studies on cellulose dissolution and regeneration in ILs.…”

Chiral ionic liquids: A compendium of syntheses and applications (2005–2012)

“…In an extension of this work, they studied the effect of bis(tetrabutylphosphonium) D-,L-tartrate CILs with the same two naproxens and reported the first example of CIL induced stereoselective fluorescence quenching by photoinduced, intramolecular electron transfer. 120 …”