The new role of dipyrromethene chemosensor for absorbance-ratiometic and fluorescence "turn-on" sensing Zn ions in water-organic solutions and real water samples.

This study presents a dipyrromethene-based sensitive and selective probe for Zn ions detection in aqueous and water-organic media. The probe demonstrates absorbance-ratiometric and "off-on" fluorescent sensing for Zn in a DMSO/HO (9:1, v/v) mixture. The 3,3',4,4',5,5'-hexamethyl-2,2'-dipyrromethene (HL), similar to its analogs, exhibits weak fluorescence (with a quantum yield of less than 0.001). However, upon the presence of Zn ions in the sensor HL solution, there is a remarkable increase (up to 200-fold) in fluorescence intensity due to the formation of a stable intramolecular chelate complex [ZnL]. This complex formation induces a significant hyperchromic effect and a red shift (57 nm) in the characteristic absorption bands. The sensing mechanism of the probe towards Zn ions was thoroughly investigated through absorbance and fluorescent titrations, molar ratio plots, H NMR, and DFT/TDDFT studies. The fluorescence response exhibited a strong linear relationship with Zn concentration within the range of 0 to 5.7 × 10 mol/L. The detection limit (LOD) and limit of quantitation (LoQ) for Zn were determined as 2 × 10 mol/L and 6.6 × 10 mol/L, respectively. Moreover, the probe demonstrated high selectivity for Zn ions over other metal ions (Na, Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, Pd, Cd, Hg, Pb). Test systems in the form of test-strips and cotton-pads were developed based on the dipyrromethene sensor for rapid "naked-eye" detection of zinc ions in water. The sensor was successfully applied for detecting Zn ions in real water samples.