All Optical Determination of Microscopic and Macroscopic Structure of Chiral, Polar Microcrystals from Achiral, Nonpolar Molecules

Organic microcrystals obtained from an octupolar molecule are studied by polarized nonlinear optical microscopy. While two-photon fluorescence microscopy is employed to verify the monocrystallinity of the analyzed domains, second-harmonic generation microscopy allowed determination of the point group symmetry of the crystallites. This combined analysis revealed that the achiral, octupolar molecules form chiral and polar conglomerate structures; the former are confirmed by circular dichroism spectroscopy. We additionally present a convenient and straightforward image analysis protocol, based on polarization dependent second-harmonic generation microscopy. This allows assessing the local organization and homogeneity of crystalline structures, which is highly relevant for technological applications, with high resolution and sensitivity.