Noninvasive Three-dimensional Assessment of Single Molecular Crystals Using Multiphoton Microscopic Observation and Their Deformation-induced Emission Characteristics.

Distinguishing the luminescence contribution from the surface and bulk of a crystal is a long-standing challenge in crystal materials. Herein, three-dimensional, multiphoton, luminescence microscope imaging of the elastic molecular single crystal 1,4-bis(4-methylthien-2-yl)-2,3,5,6-tetrafluorobenzene, was conducted. Further, the luminescence contribution from the surface and bulk of the crystal was experimentally distinguished. Strong luminescence was observed only from the surface of the crystal, while the bulk did not emit strongly. Furthermore, the surface and bulk luminescence behavior responded well to the mechanical shape change of the crystal; i.e., strong luminescence was observed for the elongated side of the crystal.