Turn‐on chemosensors for silver ions based on oligomers with diaza‐16‐crown 6‐ether receptors and aromatic fluorophore end groups

The reaction of N‐(2,4‐dinitrophenyl)pyridinium chloride ( 1 ), diaza‐18‐crown 6‐ether (DA18C6) and 2,5‐bis(aminophenyl)‐1,3,4‐oxadiazole ( 2 ) caused the opening of the pyridinium ring and yielded an ionic oligomer (oligomer‐1) comprising a 5‐DA18C6‐penta‐2,4‐dienylideneammonium chloride main chain and 2‐(4‐aminophenyl)‐5‐phenyl‐1,3,4‐oxadiazole or 2‐(4‐N‐phenylpyridinium)‐5‐phenyl‐1,3,4‐oxadiazole end groups. Accordingly, the reaction of 1 , DA18C6 and 2,7‐diaminofluorene ( 3 ) yielded oligomer‐2. The structures of oligomer‐1 and oligomer‐2 were determined by comparing their ¹H NMR spectra with those of model compounds, which were synthesized by the 1:1 reaction of 1 with 2 or 3 . Oligomer‐1 and oligomer‐2 exhibited weak bluish‐green photoluminescence (PL) before the inclusion of Ag⁺ in the DA18C6 receptor, after which they exhibited strong bluish‐green PL. These observations can be explained by the occurrence of photoinduced electron transfer in the oligomers. Copyright © 2011 Society of Chemical Industry