Rational design of perfectly oriented thermally activated delayed fluorescence emitter for efficient red electroluminescence

How to control the dipole orientation of organic emitters is a challenge in the field of organic light-emitting diodes (OLEDs). Herein, a linear thermally activated delayed fluorescence (TADF) molecule, PhNAI-PMSBA, bearing a 1,8-naphthalimide-acridine framework was designed by a double-site long-axis extension strategy to actively control the dipole orientation. The horizontal ratio of emitting dipole orientation of PhNAI-PMSBA reaches 95%, substantially higher than that of isotropic emitters (67%). This unique feature is associated with the intrinsically horizontal molecular orientation of PhNAI-PMSBA and the good agreement between its transition dipole moment direction and molecular long axis. The PhNAI-PMSBA-based OLED achieves an ultrahigh optical outcoupling efficiency of 43.2% and thus affords one of the highest red electroluminescence with an external quantum efficiency of 22.3% and the Commission International de l'Eclairage 1931 coordinates at around (0.60, 0.40).

Automated summary

This study successfully achieved active control of the dipole orientation of organic emitters by designing a linear TADF molecule, PhNAI-PMSBA, with an emitting dipole orientation ratio of 95%, substantially higher than traditional emitters. This unique feature is attributed to the inherently horizontal molecular orientation of the molecule and the good agreement between its transition dipole moment direction and molecular long axis.