Dipyrromethene-based colorimetric and fluorescent sensors for the monitoring Zn ions in aqueous media and food additives.

Using 3,3',5,5'-tetramethyl-2,2'-dipyrromethene (1), its meso-phenyl derivative (2) and 3,3',5,5'-tetraphenyl-2,2'-dipyrromethene (3), the influence of the arylation effects of the meso-spacer and pyrrole cores of dipyrromethene bidentate chelate ligands (HL) on their colorimetric and fluorescent sensory characteristics towards Zn ions in solutions was studied. The action of the sensors was based on the coordination reaction of dipyrromethene ligands by Zn ions with the formation of stable (lgK = 5.2-8.9) intramolecular chelate complexes [ZnL]. It was found that the spectral responses of the reactions of HL with Zn(AcO) in DMF/HO (9:1, v/v) differ greatly depending on the peripheral substitution nature of the dipyrromethene core. The analytical reaction of 3,3',5,5'-tetramethyl-2,2'-dipyrromethene 1 with Zn(AcO) is accompanied by bright color responses and high sensitivity of chromophore (LOD = 1.7 × 10 M) and fluorescent (LOD = 4 × 10 M) detection of the analyte. Arylation of the meso-spacer of 3,3',5,5'-tetramethyl-2,2'-dipyrromethene leads to almost complete suppression of the fluorescence response (fluorescence enhancement factor ∼ 4) of reaction of 2 with the analyte. Sensitivity of chromophore-ratiometric detection of Zn ions: LOD is 1 × 10 M. Arylation of the pyrrole rings of ligand 3 leads to a significant decrease in the sensitivity of both spectrophotometric and fluorescent detection of the analyte. For the first time, encouraging results of practical application of dipyrromethene sensor 1 in the analysis of Zn ions in samples of distilled and atmospheric water from melted snow, as well as extracts from food additives, were demonstrated.