Multiple naphthalimide dimers polymorphs triggered solvatofluorochromism, solid-state emission and aggregation-induced emission by different interaction and its application in fluorescence ratiometric sensing of dichloromethane and 1,4-dioxane

Understanding the structure–property relationships of solid-state, solution luminescence and aggregation-induced emission (AIE) at the molecular level could greatly develop efficient organic light-emitting materials. However, intermolecular π···π interaction were always considered to quench fluorescence. By contrast, a diametrically opposed effect was recently found in a class of naphthalimide polymorphs. In this work, naphthalimide derivative ND showed solvatofluorochromic properties, which attributed to the interaction of ND with different solvents resulted in ND polymorphs directly and these polymorphs formed dimers in crystallization states. Apart from the different structural motifs, torsion angles, π···π, CH···π and other supramolecular interactions made a significant difference between these polymorphs. Also, these polymorphs displayed distinctly different luminescent color in solids under 365 nm UV light. Obvious AIE characteristics were observed in aqueous mixtures. The X-ray diffraction analysis suggested that the π···π stacking interaction was the critical element that determined the solid-state emission and AIE in aqueous solution and CH···π interaction governed solvatofluorochromism. In addition, the solvents-protomed polymorphs interconversion provided a new pathway for the colormetric and ratiometric sensing of dichloromethane and 1,4-dioxane.