A novel design strategy for suppressing efficiency roll-off of blue thermally activated delayed fluorescence molecules through donor-acceptor interlocking by C-C bonds
Journal
Nanomaterials
Date
2019.12.05
Abstract
The short material lifetime of thermally activated delayed fluorescence (TADF) technology is a major obstacle to the development of economically feasible, highly efficient, and durable devices for commercial applications. TADF devices are also hampered by insufficient operational stability. In this paper, we report the design, synthesis, and evaluation of new TADF molecules possessing a sterically twisted skeleton by interlocking donor and acceptor moieties through a C？C bond. Compared to C？N-bond TADF molecules, such as CPT2, the C？C-bond TADF molecules show great dihedral angle increase by more than 30 times and a singlet？triplet energy-gap decrease to less than 0.22 eV because of the steric hindrance caused by the direct C？C bond connection. With the introduction of dibenzofuran core structure, devices comprising BMK-T317 and BMK-T318 exhibit magnificent display performance, especially their external quantum efficiencies, which is as high as 19.9 and 18.8％, respectively. Moreover, the efficiency roll-off of BMK-T318 improves significantly (26.7％). These results indicate that the material stability can be expected through the reduction of their singlet-triplet splitting and the precise adjustment of dihedral angles between the donor？acceptor skeletons.