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

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).近年来，针对Al³⁺的选择性光学传感器研究呈现激增态势，此类传感器涵盖简单希夫碱（Schiff bases）乃至其他复杂有机骨架结构。然而，此类研究报告中超过约95%缺乏晶体学证据，针对Al³⁺结合位点的推测仅基于光谱学证据。本研究合成并对一种喹啉亚胺衍生物（CMO）进行了全面表征，同时借助晶体学证据探究了其高效检测Al³⁺的应用潜力。CMO中原存的非辐射光诱导电子转移（photoinduced electron transfer, PET）与激发态分子内质子转移（excited state intramolecular proton transfer, ESIPT）过程，会因Al³⁺诱导产生的螯合增强荧光（chelation enhanced fluorescence, CHEF）效应受到抑制，最终观测到开启型荧光响应，发射强度提升18倍。所开展的理论计算结果与实验数据吻合良好。此外，本研究还探究了CMO·Al³⁺复合物通过两种不同化学途径实现荧光淬灭的过程，以此完成对无机焦磷酸（PPi）与烈性炸药苦味酸（PA）的高灵敏、高选择性检测。本研究还在活体人体癌细胞（MCF-7）中开展了Al³⁺与PPi的生物成像实验。