Hydroxychalcone dyes that serve as color indicators for pH and fluoride ions

• Published in: RSC advances Vol. 1; no. 61; pp. 37463 - 37472
• Main Authors: Du, Yanqing, Liang, Fengying, Hu, Mixia, Bu, Ren, Wang, Meiling, Tsuda, Akihiko, Eerdun, Chaolu
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 12.10.2020; The Royal Society of Chemistry
• Subjects: Absorption spectra; Aromatic compounds; Bonding strength; Carbonyl groups; Carbonyls; Charge transfer; Chemistry; Color; Crystallography; Dyes; Fluorides; Halochromism; Hydrogen bonding; Indicators; NMR; Nuclear magnetic resonance
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d0ra06719a

A chalcone, which is composed of two aromatic rings bridged by an α,β-unsaturated carbonyl group, exhibits a variety of biological activities. With an objective to develop a novel chalcone-based functional dye, we have synthesized a chalcone diol CLN 1 , bearing two OH groups at the 2-positions on both phenyl rings, as well as reference compounds CLN 2-6 , and found that it serves as color indicators for pH and fluoride ions. CLN 1 showed a vivid color change from colorless to yellow (halochromism) in water at pH ≥ 10. Furthermore, it presented a selective color change from colorless to red upon the addition of TBAF in an organic solvent such as CH 3 CN. CLN 1 provided a strong red-shifted absorption band in the visible region under alkaline conditions in water and upon the addition of TBAF in CH 3 CN. The absorption spectral study together with TD-DFT calculations and X-ray crystallographic analysis revealed that the characteristic π-resonant structures of CLN 1 caused by the ionization or OH-F − interactions and the planar conformation due to its intramolecular hydrogen bonding may provide a strong charge transfer (CT) absorption in the visible region. A chalcone diol shows visible color changes upon sensing pH of water and fluoride ions in an organic solvent.