1H-Pyrazolo[3,4-b]quinoline derivative with the chelating substituent: Synthesis and spectral properties as a fluorescent sensor for cation detection

A new fluorescent 1H-pyrazolo[3,4-b]quinoline derivative (PQ4K) with a crown moiety was synthesized and investigated as a potential sensor for certain cations. Ultraviolet–visible spectroscopy was used to investigate the spectral properties of PQ4K. The compound absorbed blue light and emitted a low intensity blue-green light. After dissolving PQ4K in methanol and acetonitrile, the fluorescence response for the presence of selected di- and trivalent ions like Zn2+, Co2+, Ni2+, Ca2+, Pb2+, Al3+, Cr3+, Cd2+, Cu2+, Hg2+ was checked. The PQ4K solutions strongly responded to some metal ions increasing the fluorescence intensity and the red shift of the fluorescence spectrum. The highest yields was observed for the Pb2+ ions in the PQ4K-methanol solution and for the Ca2+, Cd2+, Pb2+ ions in the PQ4K-acetonitrile solution. No increase in the fluorescence intensity for Hg2+ ions was observed. Much higher quantum yields were observed for solutions with acetonitrile than with methanol.