Photophysical Properties of Luminescent Zinc(II)‒Pyridinyloxadiazole Complexes and their Glassy Self-Assembly Networks

Three multifunctional ligands containing 2,5-disubstituted-oxadiazole units including an ortho/meta/para-substituted pyridine moiety have been synthesized. The reactions of the ligands with zinc(II) acetate in pyridine gave crystalline complexes with the general formula [Zn(L_i)₂py₂]. On the other hand, zinc-assisted self-assembly of the ligands in the absence of pyridine led to stable glassy networks with the general stoichiometry [Zn(L_i)₂]. The direct involvement of the pyridine moiety in the coordination of the metal was observed in all cases. The spectroscopic behaviour of the complexes was explored and compared. In particular, medium-to-high photoluminescent quantum yields were observed for thin films produced from both crystalline and glass samples. Molecular and periodic calculations were performed by using DFT to rationalize the photophysical behaviour.