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 (τTADF) and high photoluminescence quantum yields (ϕPL), 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.

快速辐射速率、高度受抑制的非辐射过程，以及较短的激子寿命，是实现高效且高电流密度下效率滚降得以抑制的热激活延迟荧光（thermally activated delayed fluorescence, TADF）有机发光二极管（organic light-emitting diodes, OLEDs）的核心要素。本研究通过将二苯甲酮（benzophenone, BP）或3-苯甲酰基吡啶（3-benzoylpyridine, BPy3）受体，分别与树枝状3,3″,6,6″-四叔丁基-9′H-9,3′:6′,9″-三咔唑（3,3″,6,6″-tetra-tert-butyl-9′H-9,3′:6′,9″-tercarbazole, CDTC）或10H-螺(吖啶-9,9′-噻吨烯)（10H-spiro(acridine-9,9′-thioxanthene), TXDMAc）给体组合，设计并合成了四种具有代表性的TADF发光体。密度泛函理论（density functional theory）模拟与X射线衍射（X-ray diffraction）分析证实，BPy3-CDTC与BPy3-TXDMAc化合物可形成CH···N分子内氢键。值得注意的是，在TADF发光体中构建分子内氢键，可显著增强分子内电荷转移（intramolecular charge transfer, ICT）强度，同时降低供体-受体（donor–acceptor, D-A）二面角，进而加速辐射过程并抑制非辐射途径。凭借较短的TADF激子寿命（τ_TADF）与高光致发光量子产率（photoluminescence quantum yields, ϕPL），采用BPy3-CDTC与BPy3-TXDMAc作为掺杂剂的OLED器件，其最大外量子效率（external quantum efficiencies, EQEs）分别可达18.9%与25.6%。此外，基于BPy3-TXDMAc的非掺杂器件展现出18.7%的最大外量子效率，在亮度为1000 cd·m⁻²时效率损耗仅为4.1%。尤为关键的是，与基于BP-CDTC的对照器件相比，天蓝色BPy3-CDTC基器件的工作寿命大幅提升了10倍，证实了内置分子内氢键策略对于实现高效稳定的TADF-OLEDs极具应用前景。