Timing Ultrafast Charge Transfer via Fano Interference beyond the Core-Hole Clock.

Ultrafast charge transfer (CT) lies at the heart of molecular and electronic functionality. We develop a Fano-based core-hole clock (FCHC) method that captures coherent coupling between localized excitons and the directly populated delocalized CT continua in resonant Auger scattering. Applied to sulfur KLL Auger spectra of a conductive organic polymer, FCHC reveals clear Fano interference and a CT time of 27±1.8  fs, demonstrating that the conventional core-hole clock model underestimates the CT dynamics timescale. We establish FCHC as a robust method for probing ultrafast CT in complex molecular systems.