Femtosecond laser-driven enantioselectivity on achiral-chiral polymorphic transition

Enantioselective crystallization is commonly controlled during nucleation from solutions. Here, we propose a facile approach to realize the enantioselective polymorphic transition of crystals in a dry state via intense femtosecond (fs)-pulsed laser irradiation. A dried metastable achiral crystal of sodium chlorate is utilized as a starting target. When circularly polarized (CP) fs laser pulses with a high repetition rate are tightly focused on the surface of the achiral crystal, a polymorphic transition to the stable chiral crystal is triggered at the focal spot. The chiral crystal is outwardly expanded even after the laser is ceased and eventually replaces the entire achiral crystal. The crystal enantiomeric excess achieves more than 20%, suggesting that the handedness of the CP light causes a chiral bias for the enantioselective polymorphic transition. The dynamics and mechanism of the enantioselective polymorphic transition are discussed based on the helical optical force exerted during the polymorphic transition process.