Brightening Quinolineimines by Al3+ and Subsequent Quenching by PPi/PA in Aqueous Medium: Synthesis, Crystal Structures, Binding Behavior, Theoretical and Cell Imaging Studies

Abstract

Recent years have witnessed an upsurge of Al3+ selective optical sensors involving simple Schiff bases to other complex organic frameworks. However, more than ∼95% of such reports lack crystallographic evidence, and proposals of binding sites for Al3+ are based upon spectroscopic evidence only. We herein synthesized and fully characterized a quinolineimine derivative (CMO) and explored its potential toward efficient detection of Al3+ with crystallographic evidence. The ongoing nonradiative photoinduced electron transfer (PET) and excited state intramolecular proton transfer (ESIPT) processes in CMO got inhibited via the chelation enhanced fluorescence (CHEF) effects induced by Al3+, and consequently turn-on fluorescence response was observed with 18-fold emission enhancements. The theoretical calculations performed were in good consonance with experimental results. We also explored further the applicability of the CMO·Al3+ complex toward highly sensitive and selective detection of inorganic phosphate (PPi) and an explosive picric acid (PA) via fluorescence quenching processes through two different chemical routes. The bioimaging of Al3+ and PPi were carried out in the living human cancer cells (MCF-7).