Ultrafast chiroptical switching in UV-excited molecules

Molecular chirality is a key design property for many technologies including bioresponsive imaging, circularly polarized light detection and emission, molecular motors and chiroptical switches. Imaging and manipulating the primary steps of transient chirality is therefore central for controlling numerous physical, chemical and biological properties that arise from chiral molecules in response to external stimuli. So far, the manifestation of electron-driven chiral dynamics in neutral molecules has not been demonstrated at their natural timescale. Here, we use time-resolved photoelectron circular dichroism (TR-PECD) to image the dynamics of coherent electronic motion in neutral chiral molecules and disclose its impact on the molecular chiral response. We report on a rapid sign inversion of the chiroptical signal occurring in ~7 fs following the UV-excitation of methyl-lactate molecules. The populated electronic coherences can be used for chiroptical switching where the amplitude and direction of the net photoelectron current generated by PECD is controlled. The interpretation of the results is supported by theoretical modelling of both the molecular photoexcitation to Rydberg states and the subsequent photoionization via PECD. Our findings establish a general method to investigate electron dynamics in a variety of chiral systems with high sensitivity and pave the way to a new scheme for enantio-sensitive charge-directed reactivity in neutral chiral molecules.