N-Heterocyclic carbene-based tetradentate platinum(ii) complexes for phosphorescent OLEDs with high brightness

Abstract

Organic light-emitting diode (OLED) is an attractive technology for display applications in high-end electronics. Tetradentate Pt(II) complexes are phosphorescence emitters of great importance for OLED fabrication. A novel series of N-heterocyclic carbene (NHC), benzocarbene (Ph/NHC) and pyridinocarbene (Py/NHC)-based tetradentate Pt(II) complexes with fused 5/6/6 metallocycles was designed and developed. Their electrochemical and photophysical properties were systematically studied through experimental and theoretical investigations, which were greatly affected by the NHC, Ph/NHC and Py/NHC. Pt(NHC-1) shows a dominant emission peak at 509 nm with a quantum efficiency of 40% and an excited lifetime of 1.8 μs in a 5 wt% doped PMMA film at room temperature. A Pt(NHC-1)-doped green OLED using 26mCPy as the host material demonstrated a very high L_max of 64 416 cd m⁻², which was a record-high value for the reported Pt(II) complex-based phosphorescent OLED. The OLED also achieved a peak EQE of 13.1% with small efficiency roll-off, which still maintained EQEs of 12.8%, 11.6% and 8.6% at a high brightness of 100, 1000 and 10 000 cd m⁻².