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

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, pi-pi 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 (EQEmax) 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. High-energy triplet exciton conversion, high exciton utilization efficiency and high device efficiency were achieved through multiple hot-exciton conversion channels.