Ligand Methylation and Coordination Geometry Effects on the Properties of Zinc and Lithium (8-Quinolinolato) Chelate Electroluminescent Materials

摘要

We present a study of the photophysical (absorption and emission) and thermal stability properties of zinc bis(8-quinolinolato) (Znq_2), lithium mono(8-quinolinolato) (Liq) chelates, and their methylated derivatives. These materials are compared with aluminum tris(8-quinolinolato) (Alq_3), which has proven to be viable for use in organic light-emitting devices (OLED's). We show that regardless of metal ion substitution the effect of ligand methylation on the photophysical and thermal properties is similar for all Mq_n materials. However, strong solvent dependence of absorption, emission and ~1H NMR chemical shifts for zinc and lithium chelates support a stronger ionic character of the metal-ligand bonding, which may have significant effects on electroluminescent properties.