Dipyrromethene as multifunctional sensor towards d-metal cations

Multifunctional sensors are becoming increasingly important because a single such compound can be used to detect ions of two or more metals. We propose a 3,3′,4,4′,5,5′-hexamethyl-2,2′-dipyrromethene (HL) as multifunctional chemosensor for absorbance ratiometric detection of Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ ions, and fluorescent detection of Zn2+, Cd2+ ions. The influence of the nature of complexing ion and medium on the thermodynamic stability of the [ML2] complexes, chromophoric and fluorescent responses of complexation reactions was analyzed. The lgKo values of [ML2] formation processes range from 4.72 to 11.08 and, regardless of the medium nature, increase in similar sequences of complexing agents: Cd2+, Ni2+, Hg2+, Co2+, Zn2+, Cu2+ – in the c-hexane/propanol-1 (30:1, v/v) and Cd2+, Hg2+, Co2+, Zn2+ – in DMF. The maximum fluorescent response (I/Io = 100–150) was observed for the reaction of dipyrromethene with Zn2+ ions. The reaction of HL with Cd(AcO)2 is accompanied by a 10-fold increase in fluorescence. Depending on the nature of the metal ion being determined and the medium, the detection limit of M2+ ions reaches 5 × 10−9–5 × 10−8 mol/L. Test-systems as HL-doped cellulose tablets were developed for detecting trace amounts of Zn2+ and Cd2+ ions in aqueous solutions. The using 3,3′,4,4′,5,5′-hexamethyl-2,2′-dipyrromethene as a multifunctional chemosensor, both chromophore detection of Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ ions and “turn-on” fluorescent sensing trace amounts of Zn2+ and Cd2+ ions can be performed. Considering the significant differences in the chromophore-fluorescent characteristics of ligands and metal complexes, dipyrromethenes have great prospects for use in cation recognition.