Pyrene-based aggregation-induced emission: A bridge model to regulate aggregation

The aggregation process plays a significant role in regulating the aggregate structures from molecules toward macroscopic photophysical properties. Pyrene (Py), as the simplest dimer candidate, serves as a suitable model for studying the aggregation. Herein, a series of Py-based aggregation-induced emission (AIE) materials have been investigated by clarifying the comprehensive roles of oxygen, substituents, molecular motion, and packing during aggregation, initially realizing the aim of controlling aggregate structures. With a largely planar and conjugated conformation, Py shows anomalous AIE characteristics due to the oxygen quenching at the molecular level but turn-on fluorescence in the aggregate state because of the oxygen isolation. Although introducing substituents induces molecular motion and similarly weakened luminescence in the molecular state, the impact of substituents on the aggregate-state photophysical properties enormously differs, exhibiting from weak blue, strong cyan, and strong green to weak yellow emissions, due to variable aggregate structures. Interestingly, the natural alicycle-substituted Py-dehydroabietylamine (Py-DAA) exhibits both mechanochromism and acidichromism, which can be synergistically applied in dynamic encryption-decryption. This work not only elucidates the unique AIE property of Py for the first time but also clarifies the bridging role of aggregation between single-molecular and aggregate states, achieving preliminary control over the aggregate structures.