Tri‐Spiral Donor for High Efficiency and Versatile Blue Thermally Activated Delayed Fluorescence Materials

Multifunctional Deep-Blue Thermally Activated Delayed Fluorescence Based on an Oxygen-Bridged Boron Acceptor for Highly Efficient Organic Light-Emitting Diodes

Until now, thermally activated delayed fluorescence (TADF) materials based on bridged boron-based acceptors have been primarily developed as dopants. However, in this study, we synthesized and characterized multifunctional deep-blue TADF materials─t-OBO-DMAC and t-OBO-DPAC─using bridged boron-based acceptors in combination with dimethylacridine or diphenylacridine as donors. These materials serve as both dopants and hosts. Theoretical calculations and experimentally measured photophysical properties of t-OBO-DMAC reveal a smaller singlet-triplet energy difference, higher photoluminescence quantum yield, and more efficient reverse intersystem crossing compared to t-OBO-DPAC. When evaluated as TADF emitters, t-OBO-DMAC and t-OBO-DPAC exhibited maximum external quantum efficiency (EQE) of 14.4 and 7.3% with deep-blue color coordinates of (0.14, 0.11) and (0.15, 0.07), respectively. Both materials were further assessed as hosts in various configurations, including host-only, TADF, phosphorescent, and phosphor-sensitized fluorescence (PSF)-emitting systems. Notably, t-OBO-DMAC demonstrated a high maximum EQE of 13.9% with deep-blue color coordinates of (0.15, 0.07) in a nondoped host-only device. Remarkably, both materials achieved EQEs exceeding 20% in the PSF devices. Our study marks a critical advancement in the field that breaks the conventional boundaries of the dopant and host and demonstrates unprecedented multifunctionalities for advanced organic light-emitting diodes.

Achieving Enhanced Thermally Activated Delayed Fluorescence Rates and Shortened Exciton Lifetimes by Constructing Intramolecular Hydrogen Bonding Channels

A fast radiative rate, highly suppressed nonradiation, and a short exciton lifetime are key elements for achieving efficient thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) with reduced efficiency roll-off at a high current density. Herein, four representative TADF emitters are designed and synthesized based on the combination of benzophenone (BP) or 3-benzoylpyridine (BPy3) acceptors, with dendritic 3,3″,6,6″-tetra-tert-butyl-9'H-9,3':6',9″-tercarbazole (CDTC) or 10H-spiro(acridine-9,9'-thioxanthene) (TXDMAc) donors, respectively. Density functional theory simulation and X-ray diffraction analysis validated the formation of CH···N intramolecular hydrogen bonds regarding the BPy3-CDTC and BPy3-TXDMAc compounds. Notably, the construction of intramolecular hydrogen bonding within TADF emitters significantly enhances the intramolecular charge transfer (ICT) strength while reducing the donor-acceptor (D-A) dihedral angle, resulting in accelerated radiative and suppressed nonradiative processes. With short TADF exciton lifetimes (τ_TADF) and high photoluminescence quantum yields (ϕ_PL), OLEDs employing BPy3-CDTC and BPy3-TXDMAc dopants realized maximum external quantum efficiencies (EQEs) up to 18.9 and 25.6%, respectively. Moreover, the nondoped device based on BPy3-TXDMAc exhibited a maximum EQE of 18.7%, accompanied by an extremely small efficiency loss of only 4.1% at the luminance of 1000 cd m^-2. In particular, the operational lifetime of the sky-blue BPy3-CDTC-based device was greatly extended by 10 times in contrast to the BP-CDTC-based counterpart, verifying the idea that the in-built intramolecular hydrogen bonding strategy was promising for the realization of efficient and stable TADF-OLEDs.