Selective chemosensing of organophosphorus pesticide ethyl parathion explored by a luminescent Ru(III)-Salophen complex in water

New ruthenium complex [RuL(PPh3)2][PF6] (1) (L, salophen = N,N-bis(salicylidene)phenylenediamine) was prepared and thoroughly characterized by different analytical methods. [RuL(PPh3)2][PF6] complex was used as molecular sensor for a quick and selective detection of ethyl parathion (EP) in pure aqueous solution. The complex was employed as a luminescent chemosensor for the detection of organophosphate pesticides such as ethyl parathion (EP), malathion (MT), cadusafos (CS) and glyphosate (GP). The results show that the complex [RuL(PPh3)2]+ is able to detect efficiently EP in neutral aqueous phase. The spectral binding, titration and interference analyses reveal that the addition of EP to ruthenium complex 1 decreases the fluorescence intensity (I0/IF = 3.86) without interference from other pesticides. The binding constant of the ruthenium complex with EP was K = 1.06 × 105 M-1. The stoichiometric ratio for the ruthenium complex with EP determined by Jobs plot was 1:1. Since two phosphines are presented trans to each other, competing for the same d orbitals of the central metal ion, one of the phosphines is being replaced by a EP; thus, the equilibrium of [RuL(PPh3)2]+ to [RuL(EP) (PPh3)]+ + PPh3 was seen in 31P NMR, where the signal corresponding to two PPh3 ligands situated trans to each other at ∼31.88 ppm was shifted to ∼46.87 ppm (PPh3 trans to EP) and new signal at ∼6.13 ppm was grown for PPh3 free. NMR experiments and DFT calculations confirm the coordination of the sulfur atom to Ru(III) (phosphorothiote in EP). The quenching of fluorescence intensity is behaved linearly with the concentration of EP up to a value of 7.26 μM and the limit of detection (LOD) was found to be 2.05 μM.