Chirality in nonlinear optics and optical switching

Chirality in molecular opto-electronics is limited sofar to the use of optically active liquid crystals and a number of optical phenomena are related to the helical macroscopic structure obtained by using one enantiomer, only. In this paper, the use of chirality in nonlinear optics and optical switching is demonstrated. The additional options offered by the combination of circularly polarized light and chiral molecules gives rise to the observation of Second Harmonic Generation from centrosymmetric crystals of a racemic mixture. This phenomenon is due to the existence of optical activity in the hyperpolarizability. Chiroptical switching is observed in inherently dissymmetric molecules, that can undergo a photochemical isomerization of a strongly dextrorotatory isomer into a strongly laevorotatory isomer. Using circular dichroism the switching between these two pseudo-enantiomers can be monitored accurately.