Recent developments in rhodamine salicylidene hydrazone chemosensors

Rhodamine spirocyclic chemosensors have attracted a lot of attention due to their simplicity, high sensitivity, and real-time detection for various analytes. Among the different types of substituents, salicylidene hydrazone is a well-known component due to its electron-donating ability and adjustable coordination cavity, which has strong sensitivity to various metal ions. In this review, the fluorescent and colorimetric sensors are classified according to their recognition and sensing categories, including Cu 2+ and Hg 2+ sensors, other metal ions sensors (Zn 2+ , Fe 3+ , Pb 2+ , Cr 6+ , Al 3+ ) , CN − and amino acid sensors. Salicylidene modulation with electron-donating groups is a powerful approach for fluorescence detection of metal ions with a nanomolar range, and the indirect sensing strategy is a good idea for the sensitive detection of anions and other species. This review article focuses mainly on advances in the field of salicylidene based rhodamine hydrazone chemosensors, concerning the spirolactam ring-opening sensing mechanism that has been developed in the last decade.