Carbazole-Based Schiff Bases: Structural Insights and Applications toward Metal Ion Detection

Carbazole-based Schiff bases have emerged as versatile chemosensors for detecting toxic and essential metal ions, addressing critical environmental and health concerns arising from metal pollution. This chapter explores their structural design, emphasizing the integration of the electron-rich carbazole core with imine (‒C=N‒) functionalities, which enhance π-conjugation, thermal stability, and selective metal coordination. Detection of transition metal ions such as Fe3+, Cr3+, Al3+, and Cu2+ has been successfully achieved using carbazole-based Schiff bases with a detection limit up to nanomolar range. Heavy metals, such as Hg and Pb, have also been detected using such materials. These sensors operate via mechanisms such as photoinduced electron transfer (PET), excited-state intramolecular proton transfer (ESIPT), chelation-enhanced fluorescence (CHEF), and aggregation-induced emission enhancement (AIEE), enabling “turn-on” or “turn-off” optical responses. This chapter highlights advancements in logic gate integration, smartphone-based detection, and AIEE-active probes for on-site monitoring. Challenges such as hydrolytic instability and aqueous solubility are addressed through structural modifications, including sulfonate groups or nanomaterial integration. Future directions emphasize push-pull architectures, near-infrared emission, and user-friendly formats like hydrogel strips. By bridging synthetic versatility with functional adaptability, carbazole-Schiff bases offer scalable solutions for environmental, industrial, and biomedical metal sensing, underscoring their potential in next-generation detection technologies.