For instance, Dong et al. studied
an organic salt as a fluorescent probe with ratiometric emission at
490 and 594 nm based on intramolecular charge transfer for Ca2+
determination. And the probe displayed high selectivity for Ca2+
and a large Stokes shift of 189 nm [16]. Wang and co-workers synthesized benzoselenadiazole based diarylamine as a near-infrared
optical sensor for F−, and the designed sensor showed a turn-on
ratiometric fluorescence signalling with F− by inhibiting the excited
state intramolecular proton transfer processes [21]. However, these
reported dyes based probes for Ca2+ and F− are faced with the poor
water solubility which severely restricts their application in water
environment systems. Moreover, synthesis of many organic dyes is
complex and expensive.