Two-Component Aggregation-Induced Emission Materials: Tunable One/Two-Photon Luminescence and Stimuli-Responsive Switches by Co-Crystal Formation

Molecular materials with aggregation-induced emission (AIE), which have been paid much attention recently, are important for applications in optoelectronic devices, chemical sensors, and biomedical probes. To date, single-component AIE systems are largely developed; however, the knowledge on the aggregation emission properties for multicomponent systems is still rather limited. In this work, it is shown that the AIE can be further extended to two-component molecular assemblies, with the (naphthylvinyl)pyridine (NP) as the model. The NP-based two-component solutions present typical AIE properties, and their aggregation/crystalline states (co-crystals) further exhibit different fluorescence emission (blue/cyan/green) with variable photoluminescence quantum yields as high as 50.4%. The co-crystals present adjustable two-photon fluorescence emission that is absent for the pristine NP solid. Moreover, NP-based co-crystals represent smart luminescent switches with reversible changes upon external stimuli (such as heat and base vapor), and the fluorescence visualization can be easily monitored benefitting from their high-efficiency photoemission and obvious color change. It can be expected that by virtue of facile design of intermolecular interactions (such as halogen/hydrogen bonds and pi-pi interactions) during co-aggregation and/or co-crystallization, the two-component AIE materials can be readily extended to other fluorphore systems toward tuning high-efficiency solid-state emission, two-photon luminescence, and stimuli-responsive switching.