Cyanide fluorescent sensors from indolium-fluorophore conjugates

Abstract

Indolium conjugated with three fluorophores including julolidine, triphenylamine, and pyrene (INJ, INT, INP) were successfully synthesized via condensation reaction with an excellent yield over 80%. All of derivatives were fully characterized and investigated the photophysical properties revealing that synthesized indolium-fluorophore conjugates has a negligible quantum yield. All synthesized compounds expressed the great selectivity toward cyanide ion indicating by colorimetric and fluorescence signal change due to internal charge transfer process (ICT) was interrupted. The sensitivity on cyanide detection was carried on both colorimetric and fluorescence mode resulting the excellent sensitivity on INT and INJ which can be operated for analysis of cyanide concentration that lower than EPA guidance. 1H-NMR, Job’s plot and mass spectrometry were used to confirm the sensing mechanism between indolium-fluorophore conjugates and cyanide. 1H-NMR indicated the 1,2-nucleophilic addition of cyanide with 1:1 ratio that provided by Job’s plot pattern. With the lowest LOD at 24 nM on fluorescence mode in aqueous system, INT was applied for real water samples analysis illustrating the high accuracy and precision with 98-106% recovery. Moreover, the preliminary result of convenient paper-based sensor for cyanide analysis was carried out successfully.