C─H···π interaction induced H-aggregates for wide range water content detection in organic solvents

J-aggregation and H-aggregation are identified as two classical models of functionally oriented non-covalent interactions, and significant attention has been drawn by researchers. However, due to the scarcity of single-crystal examples of H-aggregation, a comprehensive understanding of the relationship between its stacking mode and optical behaviour has been hindered. In recent studies, two polyaromatic Schiff base compounds, Cl-Salmphen and H-Salmphen, were successfully synthesized, and both were found to exhibit H-aggregation. In the findings, H-Salmphen was shown to display typical C─H···π interactions, characteristic of Aggregation-Induced Emission (AIE) active molecules, whereas its halogenated counterpart was identified as behaving similar to Aggregation-Caused Quenching (ACQ) active molecules. These types of results suggest that identical intermolecular interactions can produce differing optical behaviours. Light was shed, at least in part, on the formation mechanisms of H-type aggregates and their luminescence properties from these observations. Additionally, the high optical signal-to-noise ratio inherent to H-aggregates was utilized for the exploration of water content detection. As an outcome, a high-performance fluorescent filter paper was developed, enabling easy real-time detection using a smartphone.