Quantum Design for Ultrafast Probing of Molecular Chirality through Enantiomer-Specific Coherent pi-Electron Angular Momentum

Abstract

Probing molecular chirality, right-handed or left-handed chiral molecules, is one of the central issues in chemistry and biochemistry. The conventional theory of optical activity measurements such as circular dichroism has been derived in the second-order processes involving electric and magnetic dipole moments, and the signals are very weak. We propose an efficient enantiomer-probing scenario for chiral aromatic ring molecules based on photoinduced coherent pi-electron rotations. In our model, the resultant laser-induced currents themselves produce a strong magnetic field. The principle for probing molecular chirality is a utilization of dynamic Stark effects of two electronic excited states. These electronic states subjected to strong nonresonant linearly polarized UV lasers become degenerate to create enantiomer-specific electronic angular momentum. A pair of enantiomers of phenylalanine was taken as an example. Enantiomer-specific coherent magnetic fluxes on the order of a few teslas can be generated in several tens of femtoseconds. The direct detection of strong coherent magnetic fluxes could be carried out by time-resolved magnetic force microscopy experiments. The results provide important implications for the measurement of effective probing of chiral aromatic molecules.