Isoquinolinylpyrazoles and pyridylisoxazoles as luminescent materials with sensorial ability towards pollutant toxic metal ions. Experimental and computational studies

Highlights: • Isoquinolinylpyrazoles and pyridylisoxazoles were synthesised and characterised. • The potential sites for metal coordination were analysed by DFT calculations. • A detectable luminescence signal is originated under complexation. • The azoles exhibit ion sensing properties in solution. - Abstract: The crystal structure and photoluminescence behaviour of two series of azole-based derivatives have been investigated. In the solid state, the compounds form head-to-tail dimers through intermolecular hydrogen bonds and emit bluish light in the range of 340–500 nm. The geometry parameters have been optimised by DFT calculations to analyse the molecular electrostatic potential (MEP) and the charge distribution in order to find the favourable molecular sites for metal interactions. The electronic properties of the frontier orbitals and their energy levels have been also measured. The compounds behave as fluorescent materials in solution and they exhibit sensorial abilities towards Hg²⁺, Pd²⁺, Pt⁴⁺, Cu²⁺, Zn²⁺ and Cd²⁺ metal ions. The ion sensing properties that the azoles present upon complexation have been followed by spectrophotometric and spectrofluorimetric titrations. Additionally, the stability constants of the complexes formed as well as the detection and quantification limits have been calculated. The best results are obtained for the detection of Zn²⁺ at concentration lower than 0.3 µM.