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 ofpaggreate (PcJ-agg), whereas it gradually converts to a form of H-aggregate (PcH-agg), driven by the pi-pi stacking and hydrophobic effects. Under ultrasonic oscillation, the transformation of the aggregated forms from Pcj-agg, to PcH-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. (C) 2016 Elsevier B.V. All rights reserved.