Exploration of ESIPT in 4,6‐<i>O</i>‐Ethylidene‐<i>N</i>‐(2‐hydroxybenzylidene)‐β‐D‐glucopyranosylamine and Its Application in Selective Turn‐on Response Toward Lu(III) ion

4,6-O-Ethylidene-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine (PL1) exhibits excited state intramolecular proton transfer (ESIPT) mechanism, which has been established by experimental and theoretical calculations. Further, PL1 selectively interacts with Lu³⁺ ion yielding a turn-on response in methanol, where the emission intensity of the former enhances (~15 fold) after metal ion interaction. The complexation has been investigated using various analytical tools like UV-visible absorption/emission, nuclear magnetic resonance spectroscopy and lifetime studies. The relative quantum yield of PL1 (0.0043) enhances to 0.1025 upon interaction with the Lu³⁺ ion. The studies on stoichiometry by Job's plot, ESI mass spectrometry and density functional theory calculations revealed the ligand-to-metal interaction in 2 : 1 ratio.