Direct Visualization of Crystal Formation and Growth Probed by the Organic Fluorescent Molecules

In this chapter, the direct visualization of crystal formation and growth probed by organic fluorescent molecules exhibiting mechanofluorochromism and displaying aggregation-induced emission (AIE) is discussed. The fluorescence observations of the evaporative crystallization can reveal a two-step nucleation model for nuclei formation. The fluorescence from the droplets showed dramatic changes depending on the molecular state, such as monomer, amorphous, and crystal polymorph. The quartz crystal microbalance (QCM) measurement also revealed the changes in the mechanical properties during the solvent evaporation. These methods provide a useful and convenient fluorescence tool for in situ crystal analysis, from which detailed experimental evidence and mechanistic insights into crystal formation and transformation can be obtained through direct fluorescence visualization with real-time, on-site, and nondestructive methods.