Detection of hydroxyaromatics in a superior manner by a water soluble fluorescent iron-complex

Abstract

The fluorescence detection of phenolic compounds and a way to crystallize out iron ions and phenolic compounds from aqueous solution are investigated. A water soluble iron complex (N,N'-bis(3-imidazolium-1-ylpropyl)naphthalenediimide)di[bis-2,6-pyridinedicarboxylateferrate] (1) having a cationic part as fluorescent species, where the cationic fluorescent part is not in direct contact with the paramagnetic iron (3+) ion is used to detect phenolic compounds in water. The iron-complex also forms inclusion complex with phenolic compounds providing a conceptual means to remove the phenolic pollutants from solution. The fluorescence emission of the complex in aqueous solution is quenched by various hydroxyaromatic compounds and provides means for their detection. The detection limits to detect common phenolic compounds are in the range 0.39 μM to 0.66 μM. The quenching constant for 2,4,6-trinitrophenol by the complex is 3.98 × 106 mol−1 which is at par with several other good quenchers used for such detection. Structural study on the inclusion complexes showed selective formation of 1:1 inclusion complex of 1 with 1,4-dihydroxybenzene, but a 1:2 inclusion complex with phenolic compounds namely 1,3,5-trihydroxybenzene, 3-nitrophenol, 4-nitrophenol. The structural study and the conformational adjustments of the inclusion complexes are presented. The formation of different inclusion complexes in one-pot provided a means to crystallize out iron ions and nitrophenols simultaneously.