Novel emissive podands based on 8-OH-quinoline: Synthesis, fluorescence materials, DFT and complexation studies

Abstract

Two novel chemosensors with podand structures (L1 and L2) derived from 1,5-bis(2-aminophenoxy)-3-oxopenthane bearing two flexible 8-hydroxyquinoline units have been synthesized and characterized.Several nitrate complexes of transition (Cu2+), post-transition (Zn2+) and lanthanide (Eu3+ and Sm3+) metal ions have been synthesized with tetrafluoroborate salts and characterized. In order to study their potential utility as fluorescent probes, the coordination ability of chemosensors (L1 and L2) towards those metal ions has been explored in solution (by UV–Vis and emission spectroscopy) and in gas phase (by MALDI mass spectrometry).Density functional theory has been employed to explore the emission properties of the three-protonation states of the chemosensor. From this study, the anomalous red shift observed in the fluorescence spectra of the dianionic sensors can be attributed to subtle structural differences between their anionic and dianionic forms. Furthermore, a plausible explanation for the low fluorescence of the neutral form is provided in the form of a non-radiative relaxation involving the imine double-bond isomerization.All new compounds have been characterized by microanalysis, melting points, IR, UV–Vis and fluorescence emission spectroscopy and MALDI-TOF-mass spectrometry.