Solvatochromic probe behavior within ternary room-temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate plus ethanol plus water solutions

The solvatochromic probe behavior within ternary BMIMPF6 + ethanol + water systems were investigated using four solvatochromic probes: pyrene, 1,3-bis(1-pyrenyl)propane, 1-pyrenecarboxaldehyde, and Reichardt's betaine dye (BMIMPF6 [1-butyl-3-methylimidazolium hexafluorophosphate] is one of the most popular room-temperature ionic liquids [RTIL]). A simplified preferential solvation model based on the weighted mole fraction probe response shows that the pyrene cybotactic region is rich in BMIMPF6 compared to the bulk. However, the 1,3-bis(1-pyrenyl)propane and 1-pyrenecarboxaldehyde solvation environments appear to be ethanol enriched. Although the aldehyde functional moiety on 1-pyrenecarboxaldehyde may explain an ethanol-rich cybotactic region, a significant decrease in bulk viscosity (more than that predicted from additivity) of BMIMPF6 upon aqueous-ethanol addition may result in an increased intramolecular excimer formation efficiency of 1,3-bis(1-pyrenyl)propane. E-T(30) values in ternary BMIMPF6 + ethanol + water solutions are higher than those observed in neat BMIMPF6 or aqueous ethanol, suggesting a local solvation environment rich in water. The results strongly suggest that the physicochemical properties of this RTIL can be modulated in a controlled fashion by adding appropriate amounts of aqueous ethanol.