Aayoosh Singh, Amit Kumar Singh, Pranjalee Yadav, Avanish Kumar Singh, Pradeep Kumar, Saripella Srikrishna, Vinod P. Singh
Abstract The development of multifunctional luminophores with tunable and stimuli‐responsive optical properties is critical for the advancement of sensing, bioimaging, and optoelectronic technologies. Herein, a novel coumarin‐based smart luminogen, ( E )‐ N '‐(1‐(7‐(diethylamino)‐2‐oxo‐2 H ‐chromen‐3‐yl)ethylidene)thiophene‐2‐carbohydrazide (ETH) is developed that exhibits pronounced multistimuli responsive behavior including aggregation‐induced enhanced emission (AIEE), solvatochromism, viscochromism, reversible mechanochromism, and acidochromism. ETH shows solid‐state fluorescence modulation on applying mechanical stress and exposing in acid/base vapor, with reversible redshifted emission. The ETH coated paper enables its practical applications in pressure‐sensitive devices and portable acid vapor detection kits. In a mixed CH 3 CN–H 2 O system, ETH functions as a solvent‐controlled dual‐mode fluorescent probe, showing a turn‐on response to Zn 2+ and a turn‐off response to Cu 2+ with high sensitivity. Job's plot revealed 2:1 ligand‐to‐metal stoichiometry for Zn 2+ and 1:1 for Cu 2+ . The fluorescent aggregates of ETH enable selective detection of Cu 2+ through a disaggregation‐induced fluorescence quenching mechanism. A portable cotton‐swab‐based test kit is developed for practical and on‐site detection of Cu 2+ . ETH demonstrates excellent biocompatibility, as predicted by in vivo fluorescence imaging in Drosophila larval gut tissues. The combination of reversible optical switching, high fluorescence quantum yield and structural adaptability establish ETH as a novel multifunctional material for sensing, live‐cell imaging, and smart optoelectronic devices.