50 femtosecond electron transfer in lactones

This study directly measures the charge separation in malachite green lactone (MGL) and phenolphthalein (PP) in aprotic media using femtosecond spectroscopy. The transient spectra show that after optical excitation a transfer process leads directly to the formation of the dimethylaniline cation in the case of MGL and to the phenol radical cation in the case of PP. Two-color pump-probe measurements with a 60 fs cross correlation reveal that the build-up time of the radical cations is 50 fs for PP in acetonitrile. This is the fastest electron transfer so far, which occurs on the time scale of inert solvation dynamics or even faster. This suggests that solvation is not a precondition to reach charge transfer state, indicating a significant role of high-frequency intramolecular vibrational mode(s) in the electron transfer process.