Abstract An oxadiazole derivative (OXD) containing symmetrical pyridine-2- formamidophenyl-binded moiety was synthesised as fluorescence turn-on sensor OA1. Its ultraviolet–visible (UV–vis) and fluorescent spectra (FS) gave prominent fluorescence enhancement only for monovalent silver ion (Ag+) in HEPES buffer solution (10 mM, pH= 7.0, DMF-H 2 O, 9: 1, v/v), which indicated the photo-induced electron transfer (PET) ...