Two novel red-emitting fluorescent chemosensors for trace water determination with high sensitivity and large Stokes shift

Water plays a crucial role in human daily life and industrial production. However, the real-time detection technology for trace water still needed to be developed. In this paper, two red-emitting fluorescent receptors (HDBF and NDBF) for the recognition of water were designed and synthesized based on the beta-diketone difluoroboron complex and natural product vanillin. The two fluorescent probes showed excellent optical properties such as large Stokes shifts (227 nm and 286 nm), long emission wavelengths (627 nm and 686 nm), and high fluorescence quantum yields (11.28% and 6.15%). The limits of detection of HDBF and NDBF for water were determined as low as 0.016% and 0.018%, respectively. Their detecting mechanism towards water was confirmed as the hydrogen-bonding interaction by H-l NMR titration analysis. Furthermore, the two fluorescent sensors were successfully utilized in probing trace water in 1,4-dioxane by utilizing wet cotton swab as carrier, which suggested their practical application value for trace water determination.