Recent Advances in Organic PET-Based Fluorometric Chemosensors for the Detection of Cu2+ Ions.

Copper is an essential trace element that plays critical roles in enzymatic catalysis, electron transport, and redox homeostasis in living systems. However, abnormal accumulation of Cu2+ due to industrial discharge, agricultural runoff, and corrosion of plumbing systems can lead to severe environmental contamination and health complications. Therefore, the development of reliable and sensitive methods for Cu2+ detection has become an urgent priority in environmental monitoring and biomedical diagnostics. Among various analytical techniques, fluorescence-based detection has emerged as a powerful approach owing to its high sensitivity, operational simplicity, rapid response, and real-time monitoring capability. In particular, organic fluorometric chemosensors have attracted significant attention due to their structural tunability, cost-effectiveness, strong emission properties, and compatibility with aqueous and biological systems. Photoinduced electron transfer (PET)-based sensors are among the most widely explored strategies in this field. In these systems, Cu2+ binding modulates the PET pathway between donor and acceptor moieties, leading to fluorescence "turn-on" or "turn-off" responses. This review summarizes recent advances (2020-2026) in organic PET-based fluorometric chemosensors for Cu2+ detection, focusing on molecular design principles, sensing mechanism, analytical performance, selectivity profiles, and practical applications in environmental and biological systems, while highlighting current challenges and future research directions. We hope this review will provide valuable insights and guidance to researchers for designing next-generation, highly efficient PET-based fluorescent probes for Cu2+sensing.