More is different: activating luminescence in aggregate via restriction of inter-molecular motion

Molecular motion is related to the structures and properties of the molecules and their aggregates. Owing to both weak intermolecular interactions and complicated interplay between molecules, the manipulation of inter-molecular motion to realize specific structures and properties as well as applications, is challenging but attractive. Here, we reported that the photoluminescence property of luminogens could be tuned by the manipulation of the inter-molecular motion based on the dynamic ionic bond between the cation of acridinium and the anion of tetraphenyl boron. The free inter-molecular motion and the strong attraction of the ionic bond in the non/less polar solvents enabled the formation of a dark state in the excited state with faint emission. In contrast, multiple ionic bonds between cation and anion together with non-covalent interactions were observed in the crystalline state. This directly contributed to the restriction of the inter-molecular motion (RIMM), and eventually gave rise to bright aggregation-induced emission. Such a RIMM model for efficient solid-state emission can be validated by several organic ionic species. More importantly, this type of “multicomponent luminogens” showed remarkable reactive oxygen species generation, which enabled them to kill bacteria even superbugs upon white-light irradiation. This study not only provided fundamental insights into the molecular motion-structure-property relationship, but also opened up the possibility of constructing highly efficient luminogens in aggregates via RIMM for advanced applications.