Electron transfer in a donor-substituted acridinium dye: evidence for dynamical solvent control

Time-resolved emission is used to explore the intramolecular excited-state electron transfer in a donor-substituted acridinium dye in a variety of solvents at room temperature. Emission decays are predominantly bi-exponential, with the faster of the two time constants being a good measure of the charge transfer time. In 14 high-polarity solvents this time is correlated to the solvation times previously measured with the solvation probe Coumarin 153 via an apparent power law, τLE→CT≈8.4〈τ〉solv0.65. In solvents less polar than acetone the times observed deviate widely from this relationship, probably due to the effects of ion pairing.