A Multifunctional Blue-Emitting Material Designed via Tuning Distribution of Hybridized Excited-State for High-Performance Blue and Host-Sensitized OLEDs

Actualizing full singlet exciton yield via a reverse intersystem crossing from the high-lying triplet state to singlet state, namely, hot exciton mechanism, holds great potential for high-performance fluorescent organic light-emitting diodes (OLEDs). However, incorporating comprehensive insights into the mechanism and effective molecular design strategies still remains challenging. Herein, three blue emitters (CNNPI, 2TriPE-CNNPI, and 2CzPh-CNNPI) with a distinct local excited (LE) state and charge-transfer (CT) state distributions in excited states are designed and synthesized. They show prominent hybridized local and charge-transfer (HLCT) states and aggregation-induced emission enhancement properties. The hot exciton mechanism based on these emitters reveals that a balanced LE/CT distribution can simultaneously boost photoluminescence efficiency and exciton utilization. In particular, a nearly 100% exciton utilization is achieved in the electroluminescence (EL) process of 2CzPh-CNNPI. Moreover, employing 2CzPh-CNNPI as the emitter, emissive dopant, and sensitizing host, respectively, the EL performances of the corresponding nondoped pure-blue, doped deep-blue, and HLCT-sensitized fluorescent OLEDs are among the most efficient OLEDs with a hot exciton mechanism to date. These results could shed light on the design principles for hot exciton materials and inspire the development of next-generation high-performance OLEDs.