Efficient Coupling of Heavy Atom Effects and Orbital Angular Momentum Towards Fast and Efficient Metal-Free Organic Phosphors

Emissive materials are the functional components in modern and emerging technologies such as organic light-emitting diodes (OLEDs), solid-state lighting, bio and chemical sensors, and data encryption. Metal-free purely organic phosphors (POPs), as a promising novel candidate, have brought milestone evolution to emissive materials in the past decade. Compared to their conventional metal-containing counterparts, these emitters have various advantages such as large design windows, readily tunable properties, easy processability, and reduced toxicity. However, due to limitations in contemporary design strategies, the intrinsic spin-orbit coupling (SOC) efficiency of POPs remains low and their emission lifetime is pinned in the millisecond regime.<br/><br/>In the recent few years, we have advanced the design rules of POPs combining a renovated interpretation of the photophysical laws regularizing their performance and a computation-driven design pipeline. A new design concept, named "HAAM", has been proposed, where the two main factors that control spin-orbit coupling (SOC) — the Heavy Atom effect and orbital Angular Momentum—are tightly coupled to maximize SOC. We also visualized orbital angular momentum descriptors in molecular design assisted by a novel set of natural transition orbital-based computation methods. Guided by this new design strategy, new POP structures have been tailor-designed with boosted intrinsic SOC efficiencies and bright room-temperature phosphorescence. Advantages of these new semiconducting materials have been realized in prototype POP-based OLEDs and various "on-off" switchable solid-state systems.