Development of a Pyrone-Fused Tricyclic Scaffold-based Ratiometric Fluorescent Probe for Al Detection.

Aluminum (Al) is environmentally abundant and can harm living organisms in various ways, such as by inhibiting root growth, damaging faunal nervous systems, and promoting tumor cell proliferation. However, the dynamics of Al in living organisms are largely unknown; thus, detecting Al in the environment and organisms is crucial. Fluorescent probes are useful tools for the selective detection of metal ions. In particular, ratiometric fluorescent probes exhibit a detection response at two different maximum fluorescence emission wavelengths; which is advantageous for avoiding the influence of background fluorescence. A novel pyrone-fused tricyclic scaffold-based ratiometric fluorescent probe for detecting Al, ethyl 11-imino-1-oxo-3-phenyl-1H,11H-pyrano[4,3-b] quinolizine-5-carboxylate (PQ), was developed in this study. The PQ fluorescence blue shifted from 505 to 457 nm upon the addition of Al. The blue shift was accompanied by a change in the fluorescence color of the PQ solution from green to blue. Fluorescence titration experiments demonstrated that the fluorescence intensity ratio at the two peaks of interest (457/505 nm) increased in a concentration-dependent manner upon the addition of Al. Moreover, this study demonstrated that a PQ-soaked paper displays a visible color change under ultraviolet light upon exposure to Al. The above results suggest that PQ is an effective ratiometric probe for the detection of Al in the environment. Future studies will be conducted to introduce various substituents and develop fluorescent probes by leveraging the fluorescence property of a pyrone-fused tricyclic scaffolds.