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.