Stacking-dependent tetracolour luminescence and mechanofluorochromic properties of an isoquinoline derivative with aggregation-induced emission

Abstract

Although nearly one-third of organic compounds have polymorphism, the presence of more than three polymorphs with definite crystalline structures in an organic molecule is very rare. Herein, an aggregation-induced-emission-active isoquinoline derivative containing ethyl (E)-2-cyano-3-phenylacrylate at the 8-position is found to have four polymorphs, which are confirmed by X-ray single-crystal analysis. The four polymorphs exhibit different solid-state emissions, including yellow, orange-yellow, orange, and red colours, which are determined to be ascribed to the different stacking arrangements rather than molecular conformations. Furthermore, these polymorphs exhibit reversible and tetracolour switching mechanofluorochromic activities due to the transition between the crystalline and amorphous states.