Solvatochromogenic flavone dyes for the detection of water in acetone Original Research Article

Two flavone dyes, 3-hydroxy-4′-N,N-dimethylaminoflavone (HMAF) and 4′-N,N-dimethylaminoflavone-3-yl methacrylate (DMAFMA), have been investigated as solvatochromogenic fluorophores for the determination of water in acetone. The solvent-dependent absorption and fluorescence spectral characteristics of HMAF and DMAFMA have been studied in a series of organic solvents and water/acetone binary mixtures. Spectral shifts of the compounds were observed in these solvents and their mixtures. DMAFMA exhibits a normal fluorescence emission in various solvents. Besides the normal emission, HMAF shows an abnormal band which is attributed to intramolecular proton transfer occurring across a pre-existing intramolecular hydrogen bond. As a result of the proximity effect, conformation change, and the formation of intra- or intermolecular hydrogen bonds, the emission intensity changes with the change in solvents polarity. A maximum change was observed for HMAF in ethanol, and for DMAFMA in tetrahydrofuran. With incremental addition of small amounts of water to HMAF and DMAFMA acetone solution, spectral red shifts of the compounds were also observed, while the changes in the fluorescence intensity were in a reverse direction for these two compounds. Owing to the formation of solvate complexes involving hydrogen bonding with the increase of water content, the fluorescence intensity of HMAF increases and that of DMAFMA decreases. HMAF fluorescence emission intensity changes as a function of water content in the 0.0–10.0% range, with a detection limit of 0.02%. By using the DMAFMA reagent, a linear range of 0.0–3.0% and a detection limit of 0.005% are achieved. Small amounts of alcohols and aldehydes show no substantial effect on the determination of water in acetone samples with the flavone dyes. The proposed methods were applied to the determination of water in reagent-grade acetone. The results agree well with those obtained by the gas chromatographic method.