The development of phenylethylene dendrons for blue phosphorescent emitters

New high triplet energy dendrons based on 1,2-diphenylethylene with and without 2-ethylhexyloxy surface groups have been developed for deep blue phosphorescent iridium(III) dendrimers. The fac-tris[1-methyl-5-(4-fluoro) phenyl-3-n-propyl-1H-[1,2,4]triazolyl]iridium(III)-cored dendrimers, bearing first generation 1,2-diphenylethylene dendrons on the ligand triazolyl and phenyl rings, were prepared in excellent yields, employing Sonogashira cross-couplings and palladium catalysed hydrogenation as the key synthetic steps. Both dendrimers showed good thermal stability although the flexible nature of the dendrons led to the materials having low glass transition temperatures. Dendrimer 15 (without the surface groups) emitted good blue phosphorescence with a solution photoluminescence quantum yield (PLQY) of 46%, Commission Internationale de l'Eclairage (CIE) co-ordinates of (0.15, 0.14) and photoluminescence peaks at 441 and 468 nm. The solution PLQY was 50% higher than the parent iridium(III) complex showing that the high triplet energy of the diphenylethylene dendrons does not quench the luminescence of the iridium(III) complex core. Dendrimer 34, which has the surface groups, had a film PLQY of 49% and CIE co-ordinates of (0.16, 0.19) with PL peaks at 441 and 469 nm.