Highly efficient deep-blue organic light-emitting diodes (OLEDs) based on hot-exciton materials with multiple triplet exciton conversion channels

Abstract

Triplet excitons in a high-lying reverse intersystem crossing (hRISC) process play an important role in realizing efficient deep-blue materials, and how to make full use of triplet excitons becomes a big challenge. Herein, three anthracene-based deep blue emitters were successfully synthesized, namely DCAT, DCAO and CNAT. Combined experimental tests and theoretical calculations reveal that all three molecules show multi-channel utilization of triplet excitons. Especially for DCAT, the large T₁–T₂ and small S₁–T₂ energy gaps, as well as the degenerate state of T₂–T₆, provide a fast and convenient channel for more triple exciton transitions from T₂ → S₁. Other conversion channels include T₁₀ → S₂ and T₁₀ → S₃, and multiple conversion channels together contribute to the high exciton utilization efficiency of DCAT of up to 60%. More importantly, by connecting large steric hindrance groups at the 9 and 10-positions of anthracene, π–π stacking was suppressed and deep-blue emission was achieved. As a result, deep-blue OLEDs based on DCAT exhibit an excellent maximum external quantum efficiency (EQE_max) of 6.8% with the Commission international de I'Eclairage (CIE) coordinates of (0.14, 0.07). These results fully demonstrate the importance of triplet excitons utilized through multi-channel pathways and provide insights into the development of high-performance deep-blue OLEDs.