New Publication in Nature
A new experimental approach provides the long-awaited tools to understand the role of electrons in the molecular chiral reactivity and offers a way to control physical and chemical properties that result from chiral interactions. The study, published in the journal “Nature”, was led by Universität Hamburg and DESY as part of a collaboration with the Centre Laser Intense et Applications (CELIA) and the Laboratoire de Chimie et Physique Quantiques (LCPQ) in France and the Max Born Institute in Berlin.
An ultrashort UV light pulse excites two chiral molecules that are mirror images of each other, called enantiomers. The light-induced electron motion generates a chiral electronic current whose rotation direction is opposite and depends on the chiral structure of each molecule; an enantio-sensitive phenomenon that is opening new perspectives for photochemical control.
Image credit: Ella Maru Studio, Inc.Abstract: Chiral molecules, used in applications such as enantioselective photocatalysis, circularly polarized light detection, and emission and molecular switches, exist in two geometrical configurations that are non-superimposable mirror images of each other. These so-called (R) and (S) enantiomers exhibit different physical and chemical properties when interacting with other chiral entities. Attosecond technology might enable influence over such interactions, given that it can probe and even direct electron motion within molecules on the intrinsic electronic timescale6 and thereby control reactivity. Electron currents in photoexcited chiral molecules have indeed been predicted to enable enantiosensitive molecular orientation, but electron-driven chiral dynamics in neutral molecules have not yet been demonstrated owing to the lack of ultrashort, non-ionizing and perturbative light pulses. Here we use time-resolved photoelectron circular dichroism (TR-PECD) with an unprecedented temporal resolution of 2.9 fs to map the coherent electronic motion initiated by ultraviolet (UV) excitation of neutral chiral molecules. We find that electronic beatings between Rydberg states lead to periodic modulations of the chiroptical response on the few-femtosecond timescale, showing a sign inversion in less than 10 fs. Calculations validate this and also confirm that the combination of the photoinduced chiral current with a circularly polarized probe pulse realizes an enantioselective filter of molecular orientations following photoionization. We anticipate that our approach will enable further investigations of ultrafast electron dynamics in chiral systems and reveal a route towards enantiosensitive charge-directed reactivity.
More information in the DESY press release.
The online publication can be found here.