Control of the horizontal dipole ratio and emission color of deep blue tetradentate Pt(II) complexes using aliphatic spacer groups

The dedication of researchers has gradually allowed organic light-emitting diodes (OLEDs) to replace liquid crystals and/or inorganic light-emitting diodes (LEDs) in displays, signage, and lighting. However, the blue-emitting materials of OLEDs exhibit low efficiency and short lifetimes. Tetradentate Pt(II) complexes have the potential to serve as the next generation of blue emitters because of their narrow emission spectra, high photoluminescence quantum yields (PLQYs), and rigid molecular structures. The horizontal dipole ratio (Θ) is one of the most important factors that determines OLED efficiency. Unfortunately, however, high-level horizontal orientation data concerning Pt(II) complexes are available for only non-doped crystalline Pt(II) complexes, which exhibit excimer emission. Herein, we report a new strategy by which to control the orientation of Pt(II) complexes doped into host materials. The use of various aliphatic groups in different positions changes the molecular orientation. Therefore, a Θ of 79% is achieved; this is the highest value thus far for doped Pt(II) complexes. Additionally, we fabricated deep blue OLEDs with CIE y values < 0.1 and external quantum efficiencies over 20% using the developed Pt(II) complexes. The results offer new guidance for how to increase the Θ of Pt(II) complexes.