Synthesis, crystal structure, luminescent properties and photo degradation of mer-tris(8-Hydroxy-quinolinato-N, O)-indium(iii) hydrate 0.5 methanol solvate

Abstract

Tris-(8-hydroxyquinioline) aluminium (Alq3) is widely used in organic light emitting diodes as an emission and electron transport layer. In this study the effect of solvent molecules, in the solid state crystal lattice, on the photoluminescence properties of synthesized mer-tris(8-Hydroxy-quinolinato-N, O)-indium(iii) hydrate 0.5 methanol solvate (mer-[In(qn)3]⋅H2O⋅0.5 CH3OH) was studied. Single crystals were obtained through a recrystallization process and single crystal X-ray diffraction was performed to obtain the unit cell structure. The main absorption peaks were assigned to ligand centered electronic transitions, while the solid state photoluminescence excitation peak at 440nm was assigned to the 0–0 vibronic state of In(qn)3. Broad emission at 510nm was observed and was ascribed to the relaxation of an excited electron from the S1–S0 level. A powder sample was annealed at 130°C for 2h. A decrease in intensity was observed and could possibly be assigned to a loss of solvent species. To study the photon degradation, the sample was irradiated with an UV lamp for ∼15h. The emission data was collected and the change in photoluminescence intensity with time was monitored. High resolution X-ray photoelectron spectroscopy (XPS) scans of the O-1s peak revealed that after annealing the binding energy shifted to lower energies indicating a possible loss of the H2O and CH3OH present in the crystal. The O-1s peak of the degraded sample indicated the possible formation of CO (∼532.5eV), COH and OCOH (∼530.5eV) on the phenoxide ring.