High Steric‐Hindrance Windmill‐Type Molecules for Efficient Ultraviolet to Pure‐Blue Organic Light‐Emitting Diodes via Hybridized Local and Charge‐Transfer Excited‐State

Abstract Hybridized local and charge‐transfer (HLCT) excited‐state compounds that enable full exciton utilization through a reverse intersystem conversion (RISC) from a high‐lying triplet to a singlet state have attracted attention. Developing high‐performance ultraviolet (UV) and blue organic light‐emitting diodes (OLEDs) is challenging due to difficulties acquiring HLCT molecules with a large energy bandgap and a high photoluminescence. Herein, a new strategy for excellent‐performance UV to blue emitters based on high steric‐hindrance windmill‐type structure is proposed. These emitters exhibit good thermal, morphological, and electrochemical stabilities, as well as HLCT excited‐state characteristics. Results suggest that OLED using CTPPI efficiently emits UV light (396 nm, CIE x,y = 0.16, 0.04) with a maximum external quantum efficiency (EQE) of 7.9% and currently ranks third in UV OLEDs. The lights of these devices are well modulated from UV/deep‐blue to pure‐blue with EQEs greater than 5% by regulating the locally excited (LE) and charge‐transfer (CT) components. Experimental and theoretical investigations indicate that harvesting triplet excitons afford high electroluminescence efficiencies via HLCT excited states in the devices. This study provides an efficient strategy to achieve high‐performance UV and blue OLEDs and offers great flexibility for material design.