Correlation between the horizontal transition dipole moment and luminescence properties of dopants in organic light-emitting diodes†

Abstract

In developing organic light-emitting diode (OLED) materials, the luminescence properties of organic emitters and their molecular orientation within the emissive layer significantly impact the luminous effect of the emitting molecules and the device's external quantum efficiency (EQE). This study employs molecular dynamics (MD) simulations to model the vacuum deposition process and density functional theory (DFT) to investigate the molecular characteristics of fluorescence and thermally activated delayed fluorescence (TADF) emitters. The investigation encompassed comprehensive emission molecules for OLEDs, including fluorescent compounds (NaphImide-n and BMA-n series) and donor–acceptor-type TADF derivatives (o-Cz–TRZ, o-DCz–TRZ, and o-TCz–TRZ). Through systematic simulations, we gained deep insight into the molecular deposition behavior, horizontal transition dipole moment distribution properties, emitter luminescence characteristics, and the correlations between these key factors. The molecular orientation and host-dopant interactions play a decisive role in governing the morphology and quantum efficiency of the resulting materials. During the deposition process, the molecular emitting dipole orientation increases following the enlargement of the horizontally oriented TDM of the dopant molecules and the intermolecular van der Waals interaction between the host and the dopant. This work successfully combined MD and DFT methodologies to enhance the understanding of the relationship between the molecular architecture and luminescence efficiency, providing insight for optimizing OLED materials and utilizing their potential for guiding the design of next-generation organic electronics for display and lighting applications.