An aggregation induced enhanced emission-active salicylaldehyde Schiff base: a selective fluorescent sensor for picric acid.

In recent luminescent materials research, the development of multifunctional aggregation induced enhanced emission (AIEE)-active molecules through simple and efficient synthetic routes has attracted considerable attention. In this study, a new fluorescence-active organic sensor is synthesized via a straightforward Schiff-base condensation between a simple diamine, N 1-tritylethane-1,2-diamine (1), and 5-(tert-butyl)-2-hydroxyisophthalaldehyde. The resulting compound, 4-(tert-butyl)-2-((E)-((2-(tritylamino)ethyl)imino)methyl)-6-((E)-((2-(tritylamino)ethyl)imino)methyl)phenol (2), was fully characterized and evaluated as a selective fluorescent probe for the detection of picric acid (PA), a widely used and highly mutagenic nitroaromatic explosive. The sensor exhibits high selectivity and sensitivity toward PA over other aromatic explosives in methanol, addressing critical environmental, health, and security concerns associated with PA contamination and misuse. Quantitative fluorescence quenching studies reveal that the sensing behavior follows the Stern-Volmer model, affording a Stern-Volmer constant K SV = 6.309 × 104 M-1 and a detection limit of 0.756 µM. Time-resolved fluorescence lifetime measurements strongly support the proposed quenching mechanism, indicating that PA is sensed through a combination of static (ground-state ion-pair/charge-transfer) and dynamic (collisional, PET-driven) quenching, consistent with the upward-curving Stern-Volmer plot and the decrease in fluorescence lifetime upon PA addition. Furthermore, the sensor demonstrates pronounced aggregation induced enhanced emission (AIEE), retaining strong emission in the aggregated state. To demonstrate practical applicability, a portable paper-based sensing platform was successfully fabricated, enabling rapid and visual detection of PA. Overall, this work presents a simple yet effective molecular design strategy for AIEE-active fluorescent sensors with potential applications in explosive detection, environmental monitoring, and portable security screening technologies.