Real-time fluorescence visualization of the evaporation crystallization process based on the AIEE mechanism

Abstract

It is difficult to study the nucleation process of crystals intuitively due to the limitations of the current methods. In this study, based on the aggregation-induced emission enhancement mechanism, phase transition and nucleation of different polymorphs of dimethyl 5-aminoisophthalate (DM5AIP) were investigated by using fluorescence changes. The relationship between fluorescence variation and solution concentration was studied, which proved that when the concentration increased, DM5AIP molecules would prefer H-aggregates in acetonitrile. The evaporation crystallization of dimethyl 5-aminoisophthalate was successfully monitored in real time by fluorescence changes. And the evolution of DM5AIP aggregation during evaporation crystallization was systemically studied by means of Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectrometry. The results showed that the solute molecules tend to form aggregates via π–π interactions in a face-to-face manner in acetonitrile, while they tend to form aggregates by staggered accumulation and C–H⋯π weak interactions in methanol. Finally, because of the obvious difference in the fluorescence color of the two polymorphs of DM5AIP, the phase transition process was successfully observed in real time.