Fluorescent and Colorimetric Indole Derivatives as Chemosensors: A Comprehensive Metal Ion Detection Review

Abstract Indole‐based compounds have emerged as versatile chemosensors for metal ion detection due to their desirable photophysical characteristics, such as strong fluorescence and tunable electronic properties. These compounds exhibit noticeable fluorescence and/or colorimetric changes upon binding with specific metal ions, making them ideal for real time and selective sensing applications. With increasing concerns over heavy metal contamination in environmental and health‐related fields, such sensors are gaining attention for their high sensitivity, selectivity, cost‐effectiveness, and rapid response. This review highlights recent progress over the past two decades in the design and application of indole‐based sensors for detecting metal ions, including Cu 2+ , Fe 2+ , Fe 3+ , Zn 2+ , Hg 2+ , Mg 2+ , Al 3+ , Ag + , Ni 2+ , and others. The sensing mechanisms are primarily governed by complexation‐induced fluorescence quenching or enhancement, often depending on the coordination environment and electronic transitions within the indole framework. Detailed discussions on coordination chemistry, binding stoichiometry (1:1 and 1:2), solvent effects, and metal–ligand interactions are included in this review. Analytical techniques, such as UV–vis and fluorescence titration are employed to determine association constants and limits of detection (LOD), thereby evaluating sensor performance.