Development and analysis of three luminescent mixed-ligand Pb(II) coordination frameworks for electroluminescent applications

This study presents the synthesis and characterization of three luminescent mixed-ligand Pb(II) coordination complexes, [Pb₂(PhN₂O₂)₄] (<b>1</b>), [Pb(PhN₂O₂)₂(phen)] (<b>2</b>) and [Pb(Cup)(dmphen)(NO₃)]_n (<b>3</b>), using lead nitrate and ligands cupferron (Cup), 1,10-phenanthroline (phen), and 2,9-dimethyl-1,10-phenanthroline (dmphen). The complexes were analyzed <i>via</i> IR and UV spectroscopy, elemental analysis, and X-ray diffraction, revealing that the presence of methyl groups on the phenanthroline ligand in dmphen led to the formation of a unique one-dimensional zigzag coordination polymer (3), while the phenanthroline-based complex (2) adopted a mononuclear structure. The molecular arrangements were influenced by substituents on the phenanthroline ligand and interactions such as Pb…π, C-H…π, π…π stacking, and hydrogen bonding. Thermogravimetric analysis confirmed the high thermal stability of the compounds. Optical studies highlighted their potential for optoelectronic applications, with compound 3 being used to fabricate organic light-emitting diodes (OLEDs). The electroluminescence (EL) spectrum of the device exhibited a blue shift compared to its photoluminescence (PL) spectrum. Electron mobility was evaluated using the space-charge-limited current (SCLC) method, and the current-voltage properties of the OLEDs were examined. The results demonstrate the potential of these Pb(II) coordination complexes as precursors for optical devices, with the ability to fine-tune their properties through ligand modification.