Rationalizing Stacking-Dependent Charge Injection Dynamics in Radical-Based Organic Light-Emitting Diodes

Luminescent radicals can achieve unit internal quantum efficiency, but solid-state performance remains limited by intricate radical/host interactions. Herein, a cluster model combined with a multi-level conformation search method was adopted to systematically investigate the modulation mechanism of stacking modes on stability and charge injection dynamics in radical/host aggregation. It is found that a quasi-parallel stacking mode with a donor moiety aligned with the host is the energetically favored configuration, which fosters compact π-π stacking, ensures favorable energy alignment and balanced charge injection. Furthermore, quasi-parallel stacking can minimize the energy difference between the charge transfer (CT) and local excited (LE) states. Such state hybridization permits the emissive CT state to borrow oscillator strength from the LE manifold, thereby resulting in a marked enhancement of the radiative transition rate. This work reveals the critical role of the radical/host interface orientation, offering theoretical insights for the rational design of high-performance radical-based optoelectronic devices.