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

Yanqing Du; Fengying Liang; Mixia Hu; Ren Bu; Meiling Wang; Akihiko Tsuda; Chaolu Eerdun

doi:10.1039/d0ra06719a

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

RSC Adv. 2020 Oct 12;10(61):37463-37472. doi: 10.1039/d0ra06719a. eCollection 2020 Oct 7.

Authors

Yanqing Du¹, Fengying Liang¹, Mixia Hu¹, Ren Bu¹, Meiling Wang¹, Akihiko Tsuda^{1

2}, Chaolu Eerdun¹

Affiliations

¹ Department of Pharmaceutical Sciences, Inner Mongolia Medical University Jinshan Economic & Technology Development District Hohhot Inner Mongolia 010110 China 20030091@immu.edu.cn.
² Department of Chemistry, Graduate School of Science, Kobe University 1-1 Rokkodai-cho, Nada-ku Kobe 657-8501 Japan tsuda@harbor.kobe-u.ac.jp.

Abstract

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 CLN1, bearing two OH groups at the 2-positions on both phenyl rings, as well as reference compounds CLN2-6, and found that it serves as color indicators for pH and fluoride ions. CLN1 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 CH₃CN. CLN1 provided a strong red-shifted absorption band in the visible region under alkaline conditions in water and upon the addition of TBAF in CH₃CN. The absorption spectral study together with TD-DFT calculations and X-ray crystallographic analysis revealed that the characteristic π-resonant structures of CLN1 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.