Construction of Mechanofluorochromic and Aggregation-Induced Emission Materials Based on 4-Substituted Isoquinoline Derivatives

Although many organic mechanofluorochromic (MFC) materials have been reported, the design strategy and formation mechanism are still unclear, and thus some of their discoveries are based on chance or a result of blind screening of some compounds. Herein, we show a strategy for constructing MFC materials from a multisubstituted isoquinoline compound with excellent crystallinity. The introduction of bromine atom at 4-position realizes the morphological change from crystalline state to amorphous state under the stimulation of external pressure, but it is not enough to generate MFC phenomenon. Similarly, although naphthalene, benzofuran, and benzothiophene endow the resultant isoquinolines with twisted molecular conformations and aggregation-induced emission (AIE) activities, no obvious solid-state emission color changes are observed. However, the introduction of 2-benzylidenemalononitrile and (E)-2-cyano-3-phenylacrylate leads not only to the AIE activities of IQ-M and IQ-A, but also to their outstanding and reversible MFC properties. The MFC activities of these two derivatives are demonstrated to come from more twisted molecular conformations, larger deformation spaces, and stronger intramolecular charge transfer compared with the other isoquinolines. This work offers important reference value for the construction of MFC and AIE materials from traditional fluorophores.