Phase-Sensitive Second Harmonic Microscopy Reveals Bipolar Twinning of Markov-Type Molecular Crystals

Abstract

Phase-sensitive second harmonic microscopy (PS-SHGM) opens up the possibility of imaging the bipolar state of Markov-type organic supramolecular crystals. During the cocrystallization of dipolar guest and nonpolar host compounds, channel-type inclusion compounds form crystals composed of adjacent macrodomains featuring opposite polarities. Through a comparison with crystals of known absolute polarity, the application of PS-SHGM allows a fast noncontact mapping of the domain structure and a determination of the absolute polarity of thin organic and other nonlinear opical crystals.