Luminescent Organosilane and Organogermane MR‐TADF Emitters for Operationally Stable Blue Organic Light‐Emitting Diodes

Abstract Improving operational stability for organic light‐emitting diode (OLED) is a hotspot in scientific research. It is proposed that silicon (Si) and germanium (Ge) can exhibit hyperconjugation effects and participate in conjugated systems, thereby stabilizing molecules’ excited and polarized states. Herein, the importance of incorporating Si and Ge in multi‐resonance thermally activated delayed fluorescence emitters is revealed to improve their luminescence efficiency and intrinsic stability. Computational studies show that introducing Si and Ge atoms can strengthen the C−Si and C−Ge bonds due to the hyperconjugation effect, resulting in higher bond dissociation energies and molecular photostability. With the efficient spin‐vibronic coupling and spin‐orbital coupling, the flexible conformations of the emitters facilitate the spin‐flip processes by enriching the characters and density of their excited states. A maximum external quantum efficiency of 30.0% for BN ‐Ge ‐based blue‐emitting OLEDs, with (Commission Internationale de l'Eclairage) CIE y ≤ 0.18 is realized. In particular, the LT 90 at 1000 cd m −2 of 48.3 and 7.1 h is achieved for BN‐Si ‐based and BN‐Ge ‐based OLEDs, respectively, using the developed deuterated SiCzCz‐d 15 and SiTriCz2‐d 16 as the hole‐transporting and host materials. It is anticipated that the study will provide insights into the design of group IV element‐containing multiple‐resonance thermally activated delayed fluorescent emitters for optoelectronics applications.