Zinc(II) bis(dipyrromethenate)s-based «Оn–Off» fluorescent sensors for xylenes

This paper presents the results of spectral-luminescence research of binuclear zinc(II) helicates with deca-, octa-, and tetramethylsubstituted 3,3′-bis(dipyrromethene)s ([Zn 2 L 2 ]) in binary mixtures of cyclohexane with m -, o - and p -xylene. Structure effects of [Zn 2 L 2 ], and aromaticity criteria of analytes (HOMA, NICS, μ ) on the fluorescence quenching efficiency of [Zn 2 L 2 ] in the presence of xylenes was considered. It was found that decamethyl substituted 3,3′-bis(dipyrromethenate)s compared to octa-, and tetramethylsubstituted-analogs shows the highest fluorescence sensitivity to the presence of aromatic compounds. Quantum-chemical modeling showed that [Zn 2 L 2 ] fluorescence quenching in the xylenes presence is caused by the formation of [Zn 2 L 2 A n ] (n = 1 or 2) supramolecular structures. High specificity of spectral-luminescent characteristics changing in the presence of xylenes provides the possibility of using [Zn 2 L 2 ] helicates as new fluorescent sensors for trace amounts (6.5–99 ppm) detection of methylbenzenes in organic media.