Lithium, zinc and scandium complexes of phosphorylated salicylaldimines: synthesis, structure, thermochemical and photophysical properties, and application in OLEDs

Abstract

The reaction of phosphorylated salicylaldimines containing the PO group either directly attached to the central benzene core (1a) or connected with it via a methylene unit (1b) with lithium and scandium hexamethyldisilazides readily afforded [κ³-O,N,O-(L–H)Li]₂ (2a,b) and [κ²-O,N-(L–H)₃Sc] (3a,b) (L – ligand) complexes in high yields. The treatment of 1b with Et₂Zn in the presence of 1,10-phenanthroline led to zinc(II) complex 4b of (L–H)₂Zn(phen) composition featuring a bidentate coordination mode of both salicylaldiminate ligands without participation of the phosphoryl groups. The structures of the complexes obtained were confirmed by the IR spectroscopic data and, in some cases, X-ray diffraction analysis. The thermal behavior of compounds 1a,b and 4b was studied by DSC. The temperature dependences of saturated vapor pressures of ligands 1a,b and complexes 2a, 4b were measured by the Knudsen effusion method. The thermodynamic parameters characterizing crystal-to-gas phase transitions were calculated. The complexes obtained were shown to possess weak photoluminescence in THF solution at room temperature. The unoptimized three-layer OLEDs based on 2a,b and 3a,b emit green light of low and moderate intensity.