Designing Highly Efficient Phosphorescent Neutral Tetrahedral Manganese(II) Complexes for Organic Light‐Emitting Diodes

Abstract Phosphorescent transition‐metal complexes have played the vital role in the rapid development of organic light‐emitting diodes (OLEDs) as the most promising candidates for next‐generation flat‐panel display and solid‐state lighting techniques. In this work, novel and low‐cost phosphorescent neutral tetrahedral manganese(II) complexes (DBFDPO‐MnX₂, X = Br, or Cl) based on dibenzofuran‐based phosphine oxide derivative as ligand are designed and synthesized. The manganese(II) complexes exhibit intense green phosphorescence with high photoluminescence quantum yields (PLQYs) of as high as 81.4% (DBFDPO‐MnBr₂). Using complex DBFDPO‐MnBr₂ as dopant, a green OLED with current efficiency (CE_max) of 35.47 cd A⁻¹, power efficiency (PE_max) of 34.35 lm W⁻¹, and external quantum efficiency (EQE_max) of 10.49% is fabricated. Interestingly, red exciplex emission is also observed in electroluminescence, arising from the interaction between the host materials (bis(2‐(2‐hydroxyphenyl)‐pyridine)beryllium (Bepp₂) or 1,3,5‐tris(2‐N‐phenylbenzimidazolyl)benzene (TPBi)) and the dopant (DBFDPO‐MnBr₂). The exciplex‐based red OLED in this study exhibits the maximum CE and PE reaching 18.64 cd A⁻¹ and 17.92 lm W⁻¹, respectively, which are among the up‐to‐date highest values for exciplex‐based red OLEDs. Beneficial from the exciplex, it has the great potential to broaden the electroluminescent spectra with manganese(II) complex.