Investigating the structure-packing-mobility relationship of pure hydrocarbon host materials in OLEDs*

Due to the increasing demand for low-cost, large-scale, and flexible display products, organic light-emitting diodes (OLEDs) have attracted widespread attention. Understanding the structure-packing-mobility relationships (SPMR) of pure hydrocarbon (PHC) host materials is essential for developing high performance host materials and consequently improving the stability of blue OLED devices.

SBF derivatives are considered promising PHC host materials for OLEDs since they exhibit high triplet energy and good thermal stability. Recent research by Poriel and colleagues extensively examined SBF dimers, delving into the intricate connection between their molecular structures and electrochemical and photophysical properties. However, the understanding of charge transport properties, a crucial aspect for host materials, and their relationship with molecular structure and packing remains unexplored. Hence, we aim to reveal the complicated SPMR of SBF derivatives.

In this work, we investigated the impact of substituent site on the charge-carrier mobility (μ) of a series of SBF dimers. The μ of these compounds were simulated via a multi-scale approach, including molecular dynamics, density-functional theory and kinetic Monte-Carlo techniques. Our results showed that the substituent sites have significant impact on two important charge transport parameters: reorganization energy (λ) and electronic coupling (V). For example, the 1,3''-SBF₂ exhibits low λ, beneficial for facilitating charge transfer, owing to the suppression of the soft vibrational modes via stereo hindrance. In contrast, the impact of substituent site on energetic disorder is small, as all SBF dimers exhibit small molecular dipole moments. Overall, 1,3''-SBF₂ exhibit balanced and facile transport for electron and hole, implying its potential as a promising host material for OLEDs—a conclusion that aligns with experimental findings.