Bio‐inspired melatonin‐naphthalimide conjugate as a biocompatible fluorescent probe for real‐time H 2 S imaging in living cells

We report probe 1 , a novel melatonin–naphthalimide‐based fluorescent probe for the rapid and sensitive detection of hydrogen sulfide (H 2 S). The probe exhibits a distinct “turn‐on” fluorescence response through the specific reduction of an azide group to an amine, a mechanism rigorously validated by spectroscopic analysis, LC/MS, and TD‐DFT calculations. Probe 1 displays high sensitivity with a detection limit of 0.19 μM and excellent selectivity over other relevant analytes. Furthermore, bio‐imaging in A549 cells confirmed its low cytotoxicity and efficient membrane permeability, enabling real‐time monitoring of intracellular H 2 S fluctuations. These results demonstrate the potential of 1 as a robust and biocompatible tool for H 2 S detection in both environmental and biological contexts.