Organic light-emitting diodes using 3- or 5-hydroxyflavone–metal complexes

3- or 5-hydroxyflavone-metal complexes were synthesized and applied to organic light-emitting diodes (OLEDs) as an emitting material and an electron transport material. When $\mathrm{bis}$ (5-hydroxyflavonato)beryllium $[{\mathrm{Be(5Fla)}}_{\mathrm{2}}]$ was used as an emitting material, the OLED showed a luminance of $\text{1900\hspace{0.5em}}{\mathrm{cd/m}}^{\mathrm{2}}$ with yellow. On the other hand, when used as an electron transport material in an organic three-layer cell, a high luminance of more than $\text{10\hspace{0.17em}000\hspace{0.5em}}{\mathrm{cd/m}}^{\mathrm{2}}$ was obtained. Furthermore, the turn-on voltage of the OLED could be lowered to 2.4 V and its lifetime was more than 1300 h. ${\mathrm{Be(5Fla)}}_{\mathrm{2}}$ was found to have a good electron transporting capability and good stability.