Influence of additives on the polymorphic manipulation of organic fluorescent crystals and its mechanism

Development of polymorphism-dependent organic fluorescent crystals through polymorphic manipulation with additives could be a potential strategy for making new materials with different functions and properties. In this work, three polymorphs of an X-shaped tetrasubstituted molecule, 2,5-bis(5-methyl-2-thienyl) terephthalaldehyde, were successfully manipulated using additives. Distinct photophysical properties between Form I (530 nm) and Form II (570 nm) were observed, which could provide a potential method for intuitively observing the polymorphic transformation and nucleation of different polymorphic forms. With the incorporation of NMR titration, computational simulation and X-ray crystallographic analysis, the mechanism of additive-induced polymorphism was carefully investigated. Different crystallization experimental results suggest that additives could inhibit the formation of Form I while promoting the formation of Form II.