Rational Design of a New AIE‐Coupled ESIPT‐Based Multi‐chromic State Depended Organo‐luminophore WithTurn‐onEmissive Response to Zn(II) in Aqueous and Solid‐state**

Abstract A newly designed multifunctional AIE‐coupled excited‐state intramolecular proton transfer (ESIPT)‐active asymmetric multichromicfluorophor ( MCF ) has been synthesized and characterized. From tedious experimental spectroscopic dissection of the photophysical properties of MCF and two supporting compounds, ( 3‐benzotriazol‐2‐yl‐2‐hydroxy‐5‐methyl‐benzaldehyde ) (R1) and ( 2‐benzotriazol‐2‐yl‐4‐methyl‐phenol ) (R2)with theoretical discussion, it has been established that ESIPT was driven exclusively towards triazole N centre involving a 6‐member H‐bonded network over imine‐N center in both solid state and solution phase. The competition of aggregation enhanced emissive feature and ACQ (aggregation caused quenching) nature of MCF were also studied thoroughly in the THF/water mixture. New classes of mechanisms are introduced regarding AIE/ACQ phenomenon, which will eradicate the limitation of designing and development of novel solid state emitters. To the best of our knowledge, this unique feature has never been achieved before. Furthermore, reversible mechanochromic fluorescence behavior upon external grinding and acidochromism nature of MCF as acid‐base switch has also been observed. In addition, MCF selectively senses Zn 2+ ion through a colorimetric and fluorescence “turn‐on” route. The actual binding site of Zn 2+ with MCF has also been established with the help of spectroscopic studies. The present study will enlighten for a new way to achieve new multifunctional organic luminescent solids.