Enantioselective separation of axial chiral olefins by laser pulses using coupled torsion and pyramidalization motions

Abstract

Quantum control of selective separation of enantiomers in a racemate using a sequence of ultrashort perpendicular propagating laser fields is demonstrated using a two-dimensional model including the coupled torsion and pyramidalization motions of an axial chiral olefin. The mechanism is demonstrated for the pre-oriented model system (4-methyl-cyclohexylidene)fluoromethane using nuclear wavepackets propagated on potential energy surfaces calculated using time dependent density functional theory (TD-DFT). The energetical degeneracy of both aR- and aS-forms is broken by using an enantioselective infrared (IR) laser pulse that excites one quantum in the achiral pyramidalization degree of freedom of one enantiomer, followed by an enantioselective ultraviolet (UV) laser field that transfers selectively this enantiomer to the electronic singlet excited state, whereas the counterpart remains unexcited in the ground state. Both, the IR and UV lasers are linearly polarized fields with defined polarizations, designed such that the interaction with one selected enantiomer vanishes, while with the other is maximized. Our results show 96% enantiomer separation within few picoseconds.