Thiourea-Functionalized Ligands for Tunable Solid-State Photoluminescence and Quenching-Based Metal Sensing

Four new thiourea-functionalized ligands based on aminopyrazole frameworks were synthesized and characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The crystal structures of all ligands, as well as a zinc(II) chloride complex, were determined. Excitation and emission properties were evaluated in both solution and solid forms for three methoxyphenyl-substituted ligands revealing bright solid-state fluorescence in two cases. For one ligand, fluorescence was quenched upon coordination to Zn(II), demonstrating its potential as a metal-responsive sensor. Hirshfeld surface analysis was used to correlate intermolecular interactions with differences in crystal packing and emission behavior, highlighting how subtle structural changes modulate solid-state photoluminescence.