Copillar[5]arene Appended Pyrene Schiff Base: Photophysics, Aggregation Induced Emission and Picric Acid Recognition

Herein, we report the synthesis of copillar[5]arene-based pyrene Schiff base 1 and its characterization by using ¹H, ¹³C NMR, FT-IR and mass spectrometry. UV-vis absorption, steady-state fluorescence and time-resolved fluorescence are done to elucidate the photophysical behaviors of 1. To understand the electronic structure of 1, density functional theory (DFT) calculations are performed. Owing to the presence of pyrene via a Schiff base linkage, compound 1 exhibits aggregation-induced emission (AIE) characteristics. It shows aggregation in aqueous THF and DMF. The aggregation behavior is successfully demonstrated by steady-state fluorescence, dynamic light scattering (DLS) and time-correlated single-photon counting (TCSPC) experiments. Experimental findings reveal that hydrophobic effect is the driving force in the formation of aggregates. As application, the aggregated state of 1 in aqueous THF fluorimetrically recognizes picric acid (PA) selectively over a series of nitro- and nonnitroaromatics with a detection limit of 1.62×10^-7 M. The emission of the aggregated state is fully quenched upon interaction with PA.