Tetradentate Platinum(II) Complexes for Highly Efficient Phosphorescent Emitters and Sky Blue OLEDs

A series
of tetradentate Pt­(II) emitters containing fused 5/6/6
metallocycles have been designed and synthesized. Molecular geometries
play a critical role in determining the photophysical properties.
Their emission spectra are significantly affected by the geometries
of the molecular core skeletons, the substituents, even hydrogen atoms,
and their positions, which are further supported by X-ray crystallographic
analyses and theoretical calculations. The generation of excimer emissions
is observed in the tetradentate 5/6/6 Pt­(II) emitters for the first
time and found to be concentration-dependent both in the solution
and solid states. All of the Pt­(II) emitters have high photoluminescent
quantum efficiency of up to 100% and luminescent lifetime as short
as 1.4 μs at room temperature, achieving a radiative rate of
7.14 × 105 s–1. Their emission color
can be easily tuned to cover the whole visible region (λmax = 464–632 nm) through selective synthetic modification
of the heteroaromatic rings of the ligands. Pt­(1-ptz)-based sky blue organic light-emitting diode (OLED) demonstrates
a maximum external quantum efficiency (EQE) of 14.5%, yet maintains
an EQE of 12.7% at a high brightness of 1000 cd/m2. This
work demonstrates that these tetradentate Pt­(II) complexes can act
as efficient phosphorescent emitters for OLED applications.