Solvent controlled intramolecular electron transfer in mixtures of 1-butyl-3-methylimidizolium tetrafluoroborate and acetonitrile

Time-resolved emission techniques were used to study the excited-state intramolecular electron transfer of 9-(4-biphenyl)-10-methylacridinium (BPAc⁺) in mixtures of 1-butyl-3-methylimidizolium tetrafluoroborate ([Im₄₁][BF₄])+ acetonitrile (ACN), a mixture previously shown to be of nearly constant polarity and nearly ideal mixing behavior. Reaction times (τ_rxn) track solvation times (τ_solv) as a function of mixture composition over a range of more than 3 orders of magnitude in τ_solv. This same correlation extends to a variety of neat dipolar solvents and ionic liquids. Reaction times are ∼2-fold larger than τ_solv over most of the range studied but appear to reach a limiting value of ∼3 ps in the fastest solvents.