An efficient and stable blue-emission OLED based on the A-π-A configuration by “hot exciton” strategy

The “hot exciton” channel, which effectively converts triplet excitons to singlet excitons from the high triplet excited state (Tn, n > 1) to the singlet excited state (Sm, m ≥ 1), can theoretically achieve 100% utilization efficiency (ηs) of the singlet excitons. In this work, two deep-blue “hot exciton”-based fluorescent emitters, IAM and TAM, with the asymmetric structure of acceptor(A)-π-acceptor(A) configuration, were designed and synthesized. Both compounds have excellent thermal stability with thermal decomposition temperatures of up to 505 and 486 °C, respectively. The outstanding thermal stability makes them easy to form amorphous films, during device vaporization, which is beneficial for luminescence. The optimized non-doped device based on IAM achieves a deep-blue emission centered at 452 nm with International Commission on Electron Emission (CIE) coordinates of (0.148, 0.145), and reaches a maximum external quantum efficiency (EQEmax) of 6.09% and a maximum luminance of 9197 cd m−2. The EQE maintains 5.1% at 1500 cd m−2, with a low efficiency roll-off, by virtue of the excellent carrier balance derived from the rational molecular regulation of IAM. The excellent deep-blue electroluminescent performance of IAM indicates that the “hot exciton” channel has unique advantages in achieving superior deep-blue emission. Meanwhile, the A-π-A design strategy is an effective way to realize the “hot exciton”, which sheds a light on the research on the “hot exciton” materials.