Symmetry breaking and birth of chirality in molecular film at the air/water interface: an approach with nonlinear optics

Second Harmonic Generation (SHG) was used to investigate the two enantiomers of a chiral bridged binaphthol derivative 1(+) and 1(-) at the air-water interface under lateral compression in a Langmuir trough. For each enantiomer, surface pressure and SH intensity were measured simultaneously during compression and decompression cycle of the molecular film. S polarized output SHG intensity as a function of the input polarization angle of the fundamental beam demonstrated the supramolecular origin for the chirality. The formation of 1(+) and 1(-) aggregates in the film was deduced from the non-vanishing SHG intensities collected for the 90 degrees input and S output polarization angles.