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.