High-efficiency red phosphorescent iridium dendrimers with charge-transporting dendrons: Synthesis and electroluminescent properties

A series of 1-phenylisoquinoline derivatives encapsulated with peripheral arylamines as dendrons are synthesized by using the Ullmann reaction and palladium-catalyzed aromatic carbon-carbon Suzuki-coupling reactions. Red-emitting dendritic iridium complexes (called G1-1, G1-2, and G2) are synthesized using the following derivatives: NN-diphenyl-3'-isoquinolin-4-bipheny]aniline, NN-di(9,9-dimethylfluorenyl-3'-isoquinolin-4-biphenylaniline, NN-di(4'-di(2'-(9',9'-dimethylfluorenyl)amine)biphenyl-3'-isoquinolin-4-biphenylaniline as the first ligands and 5-methyl-3-(pyridin-2'-yl)-1H-1,2,4-triazole as an ancillary ligand. The obtained dendrimers are soluble in common organic solvents, and uniform thin films can be spin-coated from such solutions. Devices fabricated from dendritic iridium complexes G1-2 and G2 with a small molecule host are fabricated by spin-coating from chloroform solution in different device configurations. G1-2 and G2 show similar device performances with maximum external quantum efficiencies (EQEs) of 12.8% and 11.8% (photons/electron) and luminous efficiency of 9.2 cd A(-1) and 8.5 cd A(-1) at 0.1 mA cm(-2), respectively. Devices based on polymer host poly(9,9-dioctylfluorene)(PFO) (30% PBD (2-(4-biphenyl)-5-(4-tert-butylphenyl-1,3,4-oxadiazole)) show a slightly higher efficiency for G1-2, with a maximum EQE of 13.9 % at a much higher current density of 6.4 rnA cm(-2) and luminance of 601 cd m(-2).