Exceptionally efficient deep blue anthracene-based luminogens: design, synthesis, photophysical, and electroluminescent mechanisms

Creation of High-Quality Deep-Blue AIE Emitter with a Crossed Long-Short Axis Structure for Efficient and Versatile OLEDs

Developing deep-blue emitters for organic light-emitting diodes (OLEDs) is critical but challenging, which requires a good balance between light color, exciton utilization, and photoluminescence quantum yield (PLQY) of solid film. Herein, a high-quality deep-blue emitter, abbreviated 2TriPE-CzMCN, is designed by introducing an aggregation-induced emission (AIE) group into a crossed long-short axis (CLSA) skeleton. Theoretical and experimental investigations reveal that the CLSA molecular design can achieve a balance between deep-blue emission and triplet-excitons utilization, while the high PLQY of the solid film resulting from the AIE feature helps to improve the performance of OLEDs. Consequently, when 2TriPE-CzMCN is used as the emitting dopant, the OLED exhibits a deep-blue emission at 430 nm with a record-high maximum external quantum efficiency (EQE) of 8.84%. When 2TriPE-CzMCN serves as the host material, the sensitized monochrome orange and two-color white OLEDs (WOLEDs) realize high EL performances that exceed the efficiency limit of conventional fluorescent OLEDs. Moreover, high-performance three-color WOLEDs with a color rendering index (CRI) exceeding 90 and EQE up to 18.08% are achieved by using 2TriPE-CzMCN as the blue-emitting source. This work demonstrates that endowing CLSA molecule with AIE feature is an effective strategy for developing high-quality deep-blue emitters, and high-performance versatile OLEDs can be realized through rational device engineering.

Triphenylene-Based Emitters with Hybridized Local and Charge-Transfer Characteristics for Efficient Nondoped Blue OLEDs with a Narrowband Emission and a Small Efficiency Roll-Off

Developing high-efficiency nondoped blue organic light-emitting diodes (OLEDs) with high color purity and low-efficiency roll-off is vital for display and lighting applications. Herein, we developed two asymmetric D-π-A blue emitters, PIAnTP and PyIAnTP, in which triphenylene is first utilized as a functional acceptor. The relatively weak charge transfer (CT) properties, rigid molecular structures, and multiple supramolecular interactions in PIAnTP and PyIAnTP can significantly enhance the fluorescence efficiency and suppress the structural relaxations to obtain a narrowband blue emission. The photophysical experiments and theoretical simulations reveal that they both exhibit a typical hybridized local and charge-transfer (HLCT) excited state and achieve high external quantum efficiency (EQE) via a "hot exciton" channel. As a result, PIAnTP- and PyIAnTP-based nondoped devices realize blue emission at 456 and 464 nm, corresponding to CIE coordinates of (0.16, 0.14) and (0.16, 0.19), narrow full width at half-maximums of 52 and 60 nm, and the high EQEs of 8.36 and 8.69%, respectively. More importantly, the PIAnTP- and PyIAnTP-based nondoped devices show small EQE roll-offs of only 5.9 and 2.4% at 1000 cd m-2, respectively. These results signify an advance in designing a highly efficient blue emitter for nondoped OLEDs.

Highly Efficient and Stable Deep-blue OLEDs Based on Narrowband Emitters Featuring Orthogonal Spiro-configured Indolo[3,2,1-de]acridine Structure

High-efficiency and stable deep-blue bottom-emitting organic light-emitting diodes with Commission Internationale de l'Eclairage y coordinates (CIE_ys) < 0.08 remain exclusive in the literature owing to the high excited-state energy of the emitters. Here, we propose the utilization of narrowband emitters to lower the excited-state energy for stable deep-blue devices by taking advantage of their high color purity. Two proof-of-concept deep-blue emitters with nitrogen-containing spiro-configured polycyclic frameworks are thereafter developed to introduce a multi-resonance effect for narrow emissions and sterically orthogonal configurations for alleviated molecular interactions. Both emitters show bright ultrapure deep-blue emissions with an extremely small full-width-at-half-maxima of only 18–19 nm, which can be maintained even in heavily doped films. Small CIE_ys of 0.054 and 0.066 are therefore measured from the corresponding electroluminescence devices with peak energies of only 2.77 eV (448 nm) and 2.74 eV (453 nm), accounting for the remarkably long LT80s (lifetime to 80% of the initial luminance) of 18 900 and 43 470 hours at 100 cd m⁻², respectively. Furthermore, by adopting a thermally activated delayed fluorescence sensitizer, impressive maximum external quantum efficiencies of 25% and 31% are recorded respectively, representing state-of-the-art performances for deep-blue devices.

An advanced concept of using ultra-narrowband emitters to improve the stability of deep-blue OLEDs is proposed and two proof-of-concept deep-blue emitters are developed.