Designed benzimidazolium salts: Modulation of fluorescence response towards metal cations in pure aqueous media

• Two new hydrophilic benzimidazolium salts with ‘receptor1–spacer1–fluorophore–spacer2–receptor2’ PET design were synthesized and the effect of statistical enhancement of PET process on emission intensities was observed.
• The photophysical properties and interaction with various metal cations were studied in pure aqueous media.
• The modulation of the fluorescence response towards metal cations was observed with the variation in the receptor arm of the PET scaffold as turn-ON response for Cr3+, Ba2+ and Fe3+ was observed with one of the sensors, the other showed a turn-OFF response for Fe3+ in pure aqueous media.

Design and synthesis of two new benzimidazolium salts based PET sensors of the type ‘receptor1–spacer1–fluorophore–spacer2–receptor2’ is described. Alteration in one of the receptor arm modulates the emission intensity as well as the fluorescence response towards different metal ions. The ligand with morpholine receptor arm exhibits good selectivity for sensing Cr(III), Ba(II) and Fe(III) by ‘turn-ON’ PET mechanism in pure aqueous media. 1H NMR studies confirmed the interaction of the morpholine nitrogen with metal ion. However, the ligand with piperidine receptor arm acted as ‘turn-OFF’ sensor for Fe(III) in pure aqueous media.

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