Multi-Scale Charge Transfer in Organic Electroluminescence.

Organic light-emitting diodes (OLEDs) have witnessed remarkable advances in both materials science and device engineering over the past three decades. Owing to their intrinsic advantages, including excellent flexibility, low driving voltage, wide viewing angles, broad color gamut, and high electroluminescent efficiency, OLEDs have successfully transitioned from laboratory to commercial applications. The key is the generation and utilization of excitons, which are bound electron-hole pairs formed within organic emitters, which play a decisive role in determining the energy efficiency of OLED-based display and lighting technologies. In particular, triplet excitons generated through charge-transfer processes are particularly important, as they critically influence the electroluminescent performance of state-of-the-art OLED devices. In this review, charge transfer mechanisms operating in organic emitters are systematically discussed and summarized, encompassing both intermolecular and intramolecular interactions, as well as short- and long-range charge-transfer processes in organic emitters. By comparing these different interaction modes, we establish a comprehensive perspective on how charge transfer governs exciton formation and emission behavior. Furthermore, a detailed structure-property relationship is analyzed, offering mechanistic insights that are intended to guide the rational molecular design of next-generation high-performance materials and devices.