Imidazolium ionic liquids in OLEDs: synthesis and improved electroluminescence of an 'ionophilic' diphenylanthracene

A 9,10-diarylanthracene having two ionophilic imidazolium tags on peripheral positions has been synthesized through a radical chain addition of 1,2-dimethyl-3-(3-mercaptopropyl)imidazolium to 9,10-distyrylanthracene. OLED cells prepared with this derivative exhibits 13.6-fold efficiency enhancement as compared to that prepared with 9,10-diphenylanthracene at the same concentration. Based on electrical conductivity measurements, this efficiency enhancement has been attributed to the blocking of spurious current flow due to ion relocation near the electrodes. The advantage of covalent attachment compared to physical mixtures of 9,10-diphenylanthracene and 1,2-dimethyl-3-(3-mercaptopropyl)imidazolium ionic liquid derives from the experimental difficulty of having an active layer with the target anthracene-to-ionic liquid ratio due to the remarkable differences in viscosity of the two components of the mixture.