To obtain luminescent lanthanide complexes with a low energy LMCT state the 2-(2'-mercaptophenyl)benzothiazolates, Ln(SSN), and 2-(2'-mercaptophenyl)benzoxazolates, Ln(OSN) (Ln = Gd, Yb), were synthesized by the reaction of amides Ln[N(SiMe)] with respective thiophenols. Ytterbium complexes were structurally characterized by X-ray diffraction analysis. Cyclic voltammetry revealed that the deprotonated mercaptophenyl ligands have significantly lower oxidation potentials than their phenoxy analogues and some β-diketones. The photophysical properties of Gd and Yb compounds were studied both in solution and in the solid state. The fluorescence spectra of the compounds in solution display the bands of the keto and enol forms of the ligands. No energy transfer from the organic part to Yb has been detected in solutions of both Yb complexes, whereas in solids an intense metal-centered emission in the near infrared region was observed. The solid Gd compounds exhibited room temperature phosphorescence caused by unusually efficient intersystem crossing facilitated by the essentially reducing properties of OSN and SSN ligands. To explain the sensitization process occurring in solids Yb(OSN) and Yb(SSN) a specific non-resonant energy transfer mechanism via a ligand to metal charge transfer state has been proposed. Based on the Yb derivatives, NIR-emitting OLEDs with 860 μW cm maximal irradiance were obtained. Their Gd counterparts showed bright electrophosphorescence (up to 1350 cd m) in the devices containing doped emission layers.

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New 8-quinolinolate (Q) complexes of yttrium (1) and ytterbium (2) were synthesized by the reactions of Cp3Y and Yb[N(SiMe3)2]3 with 3 equiv. of 8-hydroxyquinoline in a DME solution. Single crystal X-ray analysis revealed the trinuclear molecular structure of the compounds Ln3Q9. The LDI-TOFMS investigation displayed that under the laser impact the compounds split off Q(-) anions to give Ln3Q8(+), Ln2Q5(+) and LnQ3(+) moieties. In the negative mode spectra the anions Q(-) and LnQ4(-) were observed. The DFT calculations showed the decreased stability of cationic Ln-quinolinolate as compared with their anionic counterparts. Complex 2 which is used as an emitter in a three-layer OLED displayed a metal-centered emission at 979 nm and an intensity of 50 μW cm(-2) at 15.5 V.