Phenyl- and Pyrazolyl-Functionalized Pyrimidine: Versatile Chromophore of Bis-Tridentate Ir(III) Phosphors for Organic Light-Emitting Diodes

There
is growing interest in the bis-tridentate Ir­(III) emitters
as they are expected to display both improved emission efficiency
and improved photostability. Herein, we turned to the new emitters m2h-1–3 and m6h-1–3, bearing a
pincer carbene ancillary and a chromophoric chelate derived from judiciously
selected phenyl-pyrimidine-pyrazole entities (pzm2hF)­H2 and (pzm6hF)­H2, which differ in terms
of the location of phenyl and pyrazole substituents on the central
pyrimidine. Density functional theory calculations revealed a notable
change in the spin density distribution from the pyrimidine-pyrazolate
entity in m2h to the pyrimidine-phenyl fragment in m6h. As a consequence, the m6h emitters exhibited
both shortened emission lifetimes and improved stabilities during
extensive photolysis in solution, while corresponding organic light-emitting
diodes (OLEDs) doped with green-emitting m6h-1 and sky-blue-emitting m6h-2 and m6h-3 exhibited external quantum efficiencies
of 17.6, 15.9, and 17.6%, respectively, superior to those of all of
their m2h counterparts at a practical luminance of 103 cd/m2. This finding suggests a new methodology
for fine-tuning the electronic transition that is important to high-performance
and durable phosphorescent OLEDs.