Realizing performance improvement of borylated TADF materials for OLEDs

A series of green to blue-emitting thermally activated delayed fluorescence (TADF) molecules (m-B-D series) centered on three-coordinated boron were designed and synthesized, denoted as m-B-PTZ, m-B-PXZ, m-B-DMAC, and m-B-SAC. Triarylborane was used as the acceptor and four different acridan derivatives were used as donors, i.e., phenothiazine, phenoxazine, dimethylacridine, and spiroacridine, to form a donor-acceptor configuration. The introduction of tert-butyl group with greater steric hindrance on the bridged benzene led to a more thermally stable architecture. In addition, the spatially constrained molecular design causes the electron donors and electron acceptors in the molecule to approach each other perpendicularly, resulting in a small energy gap between the singlet and triplet excited state. In addition, the additional tert-butyl group reduced the photoisomerization caused by the auxiliary donor, thereby preventing energy quenching and improving the photoluminescence quantum yield. Consequently, the devices obtained using m-B-DMAC as the TADF emitter exhibited an emission wavelength of 480 nm and the maximum external quantum efficiency (EQE) of 14.3%, as well as an extremely low turn-on voltage of 2.9 V. The blue-emitting devices obtained using m-B-SAC demonstrated an emission wavelength of 471 nm and the peak EQE of 12.2%. Furthermore, m-B-PTZ and m-B-PXZ both correspond to green-emitting devices, showing EQEs of 14.0 and 10.1%, respectively. This improvement in thermal stability, emission color, and efficiency indicates that our molecular designs are promising strategies for obtaining borylated TADF-organic light-emitting diodes with outstanding electroluminescent performances. [Display omitted] •A series of green to blue-emitting thermally activated delayed fluorescence (TADF) molecules centered on three-coordinated boron were designed and synthesized, realizing excellent performances.•The TADF OLED employing m-B-DMAC as an emitter exhibited blue emission at 480 nm and achieved an optimum performance with a maximum EQE of 14.3% with the low efficiency drop of 8% at 102 cd m−2.