Hydroxychalcone Color Indicators for pH and Fluoride Ion

Chalcone, an α,β-unsaturated carbonyl group bridged aromatic compound, exhibits a variety of biological activities. With an objective to develop a novel chalcone-based functional dye, we have synthesized a chalcone diol, bearing two hydroxyl groups (-OH) at the 2-positions on both phenyl rings. This new chalcone derivative was then employed as a color indicator for pH and fluoride ion^[1]. The chalcone diol showed a vivid color change from colorless to yellow (halochromism) in water at pH ≥ 10. In CH₃CN, this chalcone diol showed a specific color change from colorless to red upon sensing of fluoride ion.

The absorption spectral study together with TD-DFT calculations and X-ray crystallographic analysis revealed that the characteristic Π-resonant structures of the chalcone diol caused by OH–F^- interactions and the planar conformation owing to its intramolecular hydrogen bonding may provide a strong charge transfer (CT) absorption in the visible region.

The observed results and the mechanisms revealed in this study provide important ideas and strategies for the future molecular design of chalcone-based chemosensors and bioactive substances.

[1] Y. Du, F. Liang, M. Hu, R. Bu, M. Wang, A. Tsuda, C. Eerdun, RSC Advances 2020, 10, 37463–37472.