In Situ Microscopic Observation of the Crystallization Process of Molecular Microparticles by Fluorescence Switching

To clearly understand the solid‐state amorphous‐to‐crystalline transformation is a long‐standing challenge because such crystallization occuring in confined environments is difficult to observe directly. We developed an in situ and real‐time imaging procedure to record the interface evolution in a solid‐state crystallization of molecular amorphous particles. The method, by employing a tetra‐substituted ethene with novel morphology‐dependent fluorescence, which can distinguish the interfaces between the crystalline and amorphous phase by fluorescence color, is a simple and practical method to probe the inner process of a molecular microparticle. The crystallization of amorphous microparticles in different cases was clearly recorded, where the perfect microparticles and those with defects demonstrate diverse destinies. The details disclosed in this observation will deepen the understanding for a series of solid‐state crystallization that we know little about before.