A Colorimetric and Ratiometric Fluorescent Probes Based on Intramolecular Charge Transfer

A new colorimetric and ratiometric fluorescent anion receptor based on 4-methyl-1-hydroxybenzo-phenone p-nitrophenylhydrazone 1, was designed and synthesized. In the compound 1, the phenolic hydroxyl moiety and the hydrazone moiety are anion binding sites and the nitrobenzene moiety is a signaling group. Upon addition of AcO-, H2PO4-, F-, the color of receptor 1 in DMSO solutions changed from yellow to purple, while no obvious color changes were observed on addition of the other anions tested. Accordingly, the sensor 1 could sense visually AcO-, H2PO4-, F- without resorting to any spectroscopic instrumentation. The binding properties of the receptor 1 with anions such as AcO-, H2PO4-, F-, Cl-, Br-, I- were investigated by UV-Vis and Fluorescent titrations. The H-1 NMR titrations further looked into the nature of host-guest interactions.