A dual-functional 8-hydroxyquinoline fluorescent probe for simultaneous detection of solvent microenvironments and trace water in organic media

Reliable detection of trace water in organic solvents is indispensable for maximizing the efficiency and safeguarding the performance of water-sensitive chemical reactions. Herein, we synthesized and characterized a highly emissive organic molecule, 2-(1-butyl-6-(butylamino)-5-methoxy-1<i>H</i>-benzo[<i>d</i>]imidazol-2-yl)quinolin-8-ol (DBIMHQ), from an 8-hydroxyquinoline-benzimidazole combination. The as-prepared DBIMHQ exhibits significant solvatochromic behavior in various solvent systems. Moreover, DBIMHQ exhibited a noticeable red shift in fluorescence and a visible color change (under UV light) in different solvent systems as their polarity increased. The positive solvatochromism was examined through solvent polarity indices like the Lippert-Mataga plot and the <i>E</i>NT parameter. Interestingly, the newly prepared molecule DBIMHQ shows a substantial change in fluorescence in aprotic/protic organic solvents upon the addition of water into the DBIMHQ-solvent system. DBIMHQ exhibited a considerable decrease in the fluorescence intensity upon interaction with less than 1% water content by volume in organic solvents within a short timescale (<30 s). Besides these changes, the DBIMHQ-THF solvent system shows a remarkable spectral shift from 517 nm to 530 nm and a color change from bright green to weak yellow upon the addition of a trace amount (1% v/v) of water. Furthermore, the intermolecular hydrogen bonding interaction between water and the fluorophore DBIMHQ was elucidated through ¹H NMR titration analysis and DFT studies. The practical applicability of DBIMHQ was demonstrated through the quantitative and qualitative analyses of water in raw food materials. In addition, a chitosan-DBIMHQ thin film was developed as a solid support for real-time detection of trace water in organic solvents.