Pure red electroluminescence from a host material of binuclear gallium complex

By using a binuclear gallium complex, ${\mathrm{bis(salicylidene-o-aminophenolato)-bis(8quinolinoato)-bisgallium(III)[Ga}}_2(\mathrm{saph}{)}_2{\mathrm{q}}_2\mathrm{],}$ as the host material, organic light emitting diodes (OLEDs) with pure red emission were developed, which used a red fluorescent dye of 4-(dicyanomethylene)-2-t-butyle-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB). ${\mathrm{Ga}}_2(\mathrm{saph}{)}_2{\mathrm{q}}_2$ proves to be of much better film-forming ability and a smaller energy gap than tris(8-quinolinolato)aluminum $({\mathrm{Alq}}_3\mathrm{).}$ And the doped device with a configuration of indium $\mathrm{tin\; oxide}{\mathrm{/N,N}}^{\prime }\mathrm{-bis-(1-naphthl)-diphenyl-}{\text{1,1}}^{\prime }\mathrm{-biphenyl-}{\text{4,4}}^{\prime }{\mathrm{-diamine/Ga}}_2(\mathrm{saph}{)}_2{\mathrm{q}}_2:$ DCJTB ${\mathrm{(2\; wt \%)/Ga}}_2(\mathrm{saph}{)}_2{\mathrm{q}}_2/\mathrm{Mg:Ag},$ exhibited a turn-on voltage as low as 2.2 V, and a pure red emission with Commission Internationale de l’Eclairage (CIE 1931) coordinates of (0.67, 0.33). The improved energy transfer gave a high current efficiency of 2.04 cd/A at 20 mA/cm², which is about two times higher than that of the doped ${\mathrm{Alq}}_3$ device. This letter indicates that developing host materials is a promising way to achieve excellent red emission OLEDs.