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Noncovalent spatial interaction has become an intriguing and important tool for constructing optoelectronic molecules. In this study, we linearly attached three conjugated units in a multi π‐stacked manner by using just one trident bridge based on indeno[2,1‐b]fluorene. To achieve this structure, we improved the synthetic approach through double C−H activation, significantly simplifying the preparation process. Due to the proximity of the C10, C11, and C12 sites in indeno[2,1‐b]fluorene, we derived two novel donor|acceptor|donor (D|A|D) type molecules, 2DMB and 2DMFB, which exhibited closely packed intramolecular stacking, enabling efficient through‐space charge transfer. This molecular construction is particularly suitable for developing high‐performance thermally activated delayed fluorescence materials. With donor(s) and acceptor(s) constrained and separated within this spatially rigid structure, elevated radiative transition rates, and high photoluminescence quantum yields were achieved. Organic light‐emitting diodes incorporating 2DMB and 2DMFB demonstrated superior efficiency, achieving maximum external quantum efficiencies of 28.6 % and 16.2 %, respectively. [ABSTRACT FROM AUTHOR]

In the realm of organic light‐emitting diode (OLED), through‐space charge transfer (TSCT) thermally activated delayed fluorescence (TADF) emitters have demonstrated remarkable achievements. Nevertheless, realizing both deep‐blue emission and high efficiency by the TSCT strategy remains a persistent challenge. Here, the novel donor‐π‐donor‐σ‐acceptor (D‐π‐D‐σ‐A) type deep‐blue TSCT emitter, namely D‐tCz‐BO, is formulated to investigate its performance in OLED. D‐tCz‐BO show a narrow deep‐blue emission and efficient TADF character (λPL = 448, FWHM = 54 nm, ΦPL = 82%, and ΔEST = 0.09 eV). More importantly, the OLED based on D‐tCz‐BO as the emitter showed a maximum external quantum efficiency (EQEmax) of 20.5%, with a Commission Internationale de l'Eclairage (CIE) coordinate of (0.14, 0.12). This represents one of the best deep‐blue TSCT‐TADF emitters to date. [ABSTRACT FROM AUTHOR]

Pure aromatic hydrocarbon materials (PHCs) represent a new generation of host materials for phosphorescent OLEDs (PhOLEDs), free of heteroatoms. They reduce the molecular complexity, can be easily synthesized and are an important direction towards robust devices. As heteroatoms can be involved in bonds dissociations in operating OLEDs through exciton induced degradation processes, developing novel PHCs appear particularly relevant for the future of this technology. In the present work, we report a series of extended PHCs constructed by the assembly of three spirobifluorene fragments. The resulting positional isomers present a high triplet energy level, a wide HOMO/LUMO difference and improved thermal and morphological properties compared to previously reported PHCs. These characteristics are beneficial for the next generation of host materials for PhOLEDs and provide relevant design guidelines. When used as a host in blue‐emitting PhOLEDs, which are still the weakest link of the field, a very high EQE of 24 % and low threshold voltage of 3.56 V were obtained with a low‐efficiency roll‐off. This high performance strengthens the position of PHC strategy as an efficient alternative for OLED technology and opens the way to a more simple electronic. [ABSTRACT FROM AUTHOR]

Red to near-infrared organic light-emitting diodes (OLEDs) utilizing thermally activated delayed fluorescence (TADF) emitters continue to exhibit significant external quantum efficiency (EQE) roll-off at high luminance levels exceeding 1000 cd m−2, attributed to the relatively modest reverse intersystem crossing rate constant (kRISC) of approximately 103–104 s−1. This study presents a novel TADF molecule, TCPP-DTPA, featuring a structurally rigid π-stacked multiple donor/acceptor design. The enhanced donor/acceptor interactions minimize the energy gap between the singlet and triplet states of the TCPP-DTPA, allowing for an efficient RISC process with a high rate constant of 4.67 × 106 s−1. The OLED utilizing TCPP-DTPA demonstrates a peak EQE of 23.5% at a wavelength of 618 nm. Additionally, notable EQE values of 7.8% and 14.9% are observed at a luminance of 1000 cd m−2 for OLEDs without and with an energy-transfer assistant dopant in the emissive layer, respectively. This research contributes to enhancing the efficiency of high-brightness red TADF OLEDs, while also offering valuable insights for the optimization of molecular design and device engineering to mitigate the electroluminescence efficiency roll-off. [ABSTRACT FROM AUTHOR]

Designing deep‐blue fluorophores with a low CIEy is an important request for organic light‐emitting diode (OLED) technology either for display applications or to develop new applications such as light source with antibacterial properties. The challenge of deep‐blue emitting OLEDs mainly relies on the difficulty to reach efficient emitters fulfilling all the characteristics desired to insure a high device performance with suitable CIE coordinates. Herein, we report on the synthesis, the physico‐chemical properties and the application as emissive layer in an OLED of two deep‐blue emitters constructed on the association of Spirofluorene‐N‐PhenylAcridine (SPA‐F) and SpiroBiFluorene (SBF) molecular fragment. Two emitters, 2,2‐SPAF‐SBF and 2,3‐SPAF‐SBF have been constructed following a similar design strategy. The emission wavelength is tuned by the substitution pattern of the SBF backbone (meta or para linkage). Through a structure/properties relationship study, the electrochemical, photophysical and thermal/morphological properties are discussed. When used as emitter in a multi‐layer OLED, 2,2‐SPA‐SBF displays a deep‐blue emission reaching an EQE of ≈1.7% and a Von of 4 V. The electroluminescent spectrum displays a λmax below 400 nm (i.e. 394 nm) and CIE coordinates of (0.182, 0.054). The CIEy coordinate of 0.054 is low and fits the NTSC and EBU standards. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes (OLEDs) with high-definition displays require narrowband emission from each pixel. Recently, boron-based thermally activated delayed fluorescence (TADF) emitters have gained broad attention in the OLED research field. They can effectively utilize both singlet and triplet excitons for electroluminescence, resulting in a small full width of half maximum (FWHM). The fused nitrogen/boron (N/B) system, known as the multi-resonance TADF (MR-TADF) system, has been making rapid progress. In this review, we summarize the current research progress in both traditional and MR-type boron derivatives with TADF characteristics from a molecular construction perspective. We discuss the molecular design strategy involved in maintaining high device efficiency and simultaneously achieving a narrowband emission profile. This review aims to provide insight and guidance for future developments for improving the stability, color purity, and performance of boron-based materials. [ABSTRACT FROM AUTHOR]