Fluorescent Sensor Based on 1<i>H</i>-Pyrazolo[3,4-<i>b</i>]quinoline Derivative for Detecting Zn²⁺ Cations

Abstract

The photophysical and sensory properties of the donor–acceptor pyrazoloquinoline derivative (PQPc) were investigated using absorption, steady-state, and time-resolved fluorescence measurements. The compound synthesized from commercial, readily available substrates exhibited absorptions in the UV–Vis range, with a maximum of the longwave band around 390 nm. The maximum fluorescence was around 460–480 nm, depending on the solvent. The quantum yield was between 12.87% (for n-hexane) and 0.75% (for acetonitrile) and decreased with increasing solvent polarity. The PET mechanism was implicated as the cause of fluorescence quenching. Divalent ions such as Zn2+, Pb2+, Cd2+, Ca2+, Mg2+, Co2+, Ni2+, and Cu2+ were introduced to study the fluorescent response of PQPc. A 13-times increase in fluorescence quantum yield was observed after the addition of Zn2+ ions. Detailed research was carried out for the PQPc-Zn2+ system in order to check the possibility of analytical applications of PQPc as a fluorescent sensor. A detection limit of Zn2+ was set at the value level 1.93 × 10−7 M. PQPc-Zn2+ complexes had a stoichiometry of 1:1 with a binding constant of 859 M−1. Biological studies showed that the sensor was localized in cells near the membrane and cytoplasm and may be used to detect zinc ions in eukaryotic cells.

Keywords

• fluorescent sensor
• pyrazoloquinoline derivative
• DFT calculation
• Zn²⁺ detection