Ratiometric fluorescent determination of palladium based on the C–N bond cleavage of allyl quaternary ammonium

Abstract

An allyl quaternary ammonium modified phenanthroimidazole derivative (AL-PPI) has been designed and synthesized for ratiometric detection of palladium. The probe AL-PPI shows high sensitivity and selectivity toward Pd⁰, with the limit of detection (LOD) of 8.46 nM in ethanol and 11.5 nM in CTAC aqueous solution, respectively. The sensing mechanism is based on Pd⁰-catalyzed C–N bond cleavage of the N-allylpyridinium moiety in AL-PPI. The fluorescence of AL-PPI can be quenched by Pd²⁺. However, by using tris(2-thiophenyl)phosphine (TFP) as the reductant and ligand, AL-PPI shows a ratiometric fluorescence response toward Pd²⁺. With the aid of TFP, the LOD of AL-PPI for Pd²⁺ is 4.29 nM. When encapsulated in CTAC micelles, the fluorescence quantum yield of AL-PPI is enhanced dramatically, which may facilitate its application in quantitative detection of palladium in practical samples.