Efficient Pure Organic Near-Infrared Room-Temperature Phosphorescence based on n/π Orbital Decoupling

Developing pure organic room-temperature phosphorescence (RTP) materials remains an enormous challenge, especially for efficient near-infrared (NIR) RTP materials. Herein, a functional unit combination strategy is employed to design a series of pure organic molecules, in which benzo[c][1,2,5]thiadiazole (BZT) serves as the main luminescent core of RTP, while the folded units are responsible for spin–orbit coupling (SOC) enhancement and emission redshift. By integrating both rigid and flexible folded units into the BZT core, we observe the n/π orbital decoupling between the folded units and the BZT core. This orbital decoupling facilitates significant interplay between orbital angular momentum and heavy-atom effect, maximizing the SOC. As a result, a molecule functionalized with thianthrene and phenyl selenide demonstrates efficient NIR RTP emission, which exhibits a maximum RTP wavelength at 705 nm and a high RTP efficiency of 10.25%, surpassing most of the reported pure organic NIR RTP materials. As an emitter, its doped organic light-emitting diode (OLED) device demonstrates excellent NIR electroluminescence with a maximum external quantum efficiency of 1.21%. To our knowledge, this work not only reports the first example of pure organic NIR phosphorescent OLED, but also reveals a n/π orbital decoupling strategy for designing highly efficient pure organic RTP materials.