Ultrasound irradiated preparation of a nanosheet assembly from lariat ethers and its application as a stimuli-responsive fluorescent indicator for silver ion in aqueous solution

Herein, an assembly of a new synthesized lariat ether (Pc) was demonstrated as a novel fluorescent indicator for the determination of silver ions in aqueous solution. The silver-specific receptor Pc was constructed by incorporating an azacrown[N,S,O] moiety into a picoline fluorophore. The UV–vis spectra revealed that the self-assembly of the stacked Pc molecules is initially in a form of J-aggreate (Pc_J-agg), whereas it gradually converts to a form of H-aggregate (Pc_H-agg), driven by the π-π stacking and hydrophobic effects. Under ultrasonic oscillation, the transformation of the aggregated forms from Pc_J-agg to Pc_H-agg would be disturbed while a formation of a new stable assembled form of Pc molecules denoted as Pc_NS was initiated. The morphology and nanosheeted structure of the new Pc_NS were revealed by atomic force microscopy and dynamic light-scattering measurement. As for the investigation of its emission property, the fluorescence spectroscopy was used and an evidently blue-shifted fluorescence was observed. When used as a stimuli-responsive fluorescent indicator, the Pc_NS assembly was degraded upon the addition of silver ions, accompanying a 44 nm bathochromic shift in its fluorescence emission spectrum. Investigation of its selectivity for various cations confirmed that the Pc_NS nanosheet assembly could be efficiently used for the detection of silver ions.