Surfactant-assisted self-assembled polymorphs of AIEgen di(4-propoxyphenyl)dibenzofulvene

Some aggregation-induced emission (AIE) substances show morphology-dependent emissions. The preparation of diverse morphologies from one AIEgen using simple physical methods remains a challenge. This article reports the systematic studies on the self-assembled polymorphs of an AIEgen, di(4-propoxyphenyl)dibenzofulvene (DBF), assisted by three types of surfactants. By varying the surfactant type and concentration, various morphologies of DBF aggregates with different sizes and shapes, such as micro-sized spherical particles, lines, dendritic structures, needles as well as large and long thin sheets, are obtained. Yellow-emitting DBF aggregates are commonly formed in the dispersions with all types of surfactants, while green-emitting aggregates are more commonly formed in the dispersions with a high concentration of Pluronic F-127 and the mixed surfactants of cetyl trimethylammonium bromide (CTAB) and sodium dodecylbenzene sulfonate (SDBS). Very impressively, green-emitting hexagonal and rhombic thin sheets and multifaceted 3D structures are also obtained. In addition, freezing-thawing treatment and mechanical stirring of the DBF dispersions lead to the formation of green-emitting particles and even blue-emitting thin sheets. XRD characterization proves the crystalline nature of the DBF aggregates. The origin of the polymorphs of DBF aggregates is explained by the interactions between DBF and surfactant molecules and the transformation from small aggregates to large ones. This work proves that polymorphs can be obtained with only one AIEgen with the assistance of surfactants. This strategy can be applied to other AIE substances for the fabrication of polymorphic crystals with outstanding luminescence properties.