Synthesis, characterization and fluorescent properties of ferrocenyl pyrazole and triazole ligands and their palladium complexes

The search for new fluorescent materials with high quantum yields has been the focus of research, considering the diverse applications that fluorescent materials present. In this study, ferrocenyl pyrazolyl (L1) and ferrocenyl triazolyl (L2) ligands and their palladium metal complexes (1 and 2) were synthesized to investigate their fluorescence properties. While the pyrazolyl ligand was prepared through a ligand substitution reaction, synthesis of the triazolyl derivative involved the [3 + 2] azide-alkyne using click chemistry. All the prepared compounds have been characterized by NMR and IR spectroscopy, elemental analysis, mass spectrometry and single-crystal X-ray crystallography. These air-stable compounds were prepared in moderate to good yields (70% and 83%). The ferrocenyl-pyrazolyl L1 and ferrocenyl-triazolyl L2 ligands showed near-infrared (NIR) emission bands with quantum yields of 20% and 26% respectively. The addition of the Pd²⁺ ions results in the reduction of fluorescence intensity and quantum yield. Such fluorescent properties demonstrate their potential use in bio-analysis and as fluorogenic probing.