Color Stable Deep Blue Multi-Resonance Organic Emitters with Narrow Emission and High Efficiency

Enhancing Spin-Orbit Coupling in an Indolocarbazole Multiresonance Emitter by a Sulfur-Containing Peripheral Substituent for a Fast Reverse Intersystem Crossing

A fast reverse intersystem crossing (RISC) remains an ongoing pursuit for multiresonance (MR) emitters but faces formidable challenges, particularly for indolocarbazole (ICz) derived ones. Here, heavy-atom effect is introduced first to construct ICz-MR emitter using a sulfur-containing substitute, simultaneously enhancing both spin-orbit and spin-vibronic coupling to afford a fast RISC with a rate of 1.2 × 105 s-1, nearly one order of magnitude higher than previous maximum values. The emitter also exhibits an extremely narrow deep-blue emission peaking at 456 nm with full-width at half-maxima of merely 12 nm and a photoluminescence quantum yield of 92%. Benefiting from its efficient triplet upconversion capability, this emitter achieves not only a high maximum external quantum efficiency (EQE) of 31.1% in organic light-emitting diodes but also greatly alleviates efficiency roll-off, affording record-high EQEs of 29.9% at 1000 cd m-2 and 18.7% at 5000 cd m-2 among devices with ICz-MR emitters.

Spin-Flip-Restricted Multiple-Resonance Emitters for Extended Device Lifetime in Indolocarbazole-Based Blue Organic Light-Emitting Diodes

In this study, a multiple-resonance (MR) core structure is developed with a spin-flip-restricted emission mechanism based on a fused indolo[3,2,1-jk]carbazole (ICz) framework as emitters to improve the lifetime of blue organic light-emitting diodes. The molecular skeleton modulation approach applied to the conjugated π-system effectively stabilizes the triplet energy of the fused ICz emitters and narrows the full-width-at-half maximum (<20 nm). In addition, the emitters exhibit higher exciton stability than conventional boron-based MR emitters. The fused ICz-based blue fluorescent device exhibits a high external quantum efficiency of 7.2%, a blue index of 68.6 cd A-1 at a Commission internationale de l'éclairage y coordinate (CIEy) of 0.075, and a device lifetime 1.8 times longer than that of a boron-based emitter. In addition, a phosphor-sensitized fluorescent device based on the ICz emitter exhibited an improved external quantum efficiency of 20.6% with a CIEy coordinate of 0.076.

Efficient Deep-Blue Multiple-Resonance Emitters Based on Azepine-Decorated ν-DABNA for CIEy below 0.06

Ultrapure deep-blue emitters are in high demand for organic light-emitting diodes (OLEDs). Although color coordinates serve as straightforward parameters for assessing color purity, precise control over the maximum wavelength and full-width at half-maximum is necessary to optimize OLED performance, including luminance efficiency and luminous efficacy. Multiple-resonance (MR) emitters are promising candidates for achieving ideal luminescence properties; consequently, a wide variety of MR frameworks have been developed. However, most of these emitters experience a wavelength displacement from the ideal color, which limits their practical applicability. Therefore, a molecular design that is compatible with MR emitters for modulating their energy levels and color output is particularly valuable. Here, it is demonstrated that the azepine donor unit induces an appropriate blue-shift in the emission maximum while maintaining efficient MR characteristics, including high photoluminescence quantum yield, narrow emission, and a fast reverse intersystem crossing rate. OLEDs using newly developed MR emitters based on the ν-DABNA framework simultaneously exhibit a high quantum efficiency of ≈30%, luminous efficacy of ≈20 lm W-1, exceptional color purity with Commission Internationale de l'Éclairage coordinates as low as (0.14, 0.06), and notably high operational stability. These results demonstrate unprecedentedly high levels compared with those observed in previously reported deep-blue emitters.

Bromine atom introduction improves the F- sensing ability of an indolo[3,2-b]carbazole-salicylaldehyde-based fluorescence turn-on sensor

The heavy-atom effect usually quenches fluorescence, but scarcely enhances it. Herein, fluorescence turn-on sensors without or with a bromine atom for F- detection are presented, achieving fast response time within 1 min, and the LODs of 1.9 × 10-7 and 8.5 × 10-8 M, reflecting that halogen atom introduction is beneficial for F- detection ability improvement. The sensing mechanism of -OH unit deprotonation is confirmed based on the results of a 1 : 2 stoichiometric ratio, 1H NMR titration and TD-DFT calculation. The water environment F- detection and spiked recovery experiments demonstrate their potential for real sample detection.

An Ideal Molecular Construction Strategy for Ultra-Narrow-Band Deep-Blue Emitters: Balancing Bathochromic-Shift Emission, Spectral Narrowing, and Aggregation Suppression

Narrowband emissive multiple resonance (MR) emitters promise high efficiency and stability in deep-blue organic light-emitting diodes (OLEDs). However, the construction of ideal ultra-narrow-band deep-blue MR emitters still faces formidable challenges, especially in balancing bathochromic-shift emission, spectral narrowing, and aggregation suppression. Here, DICz is chosen, which possesses the smallest full-width-at-half-maximum (FWHM) in MR structures, as the core and solved the above issue by tuning its peripheral substitution sites. The 1-substituted molecule Cz-DICz is able to show a bright deep-blue emission with a peak at 457 nm, an extremely small FWHM of 14 nm, and a CIE coordinate of (0.14, 0.08) in solution. The corresponding OLEDs exhibit high maximum external quantum efficiencies of 22.1%-25.6% and identical small FWHMs of 18 nm over the practical mass-production concentration range (1-4 wt.%). To the best of the knowledge, 14 and 18 nm are currently the smallest FWHM values for deep-blue MR emitters with similar emission maxima under photoluminescence and electroluminescence conditions, respectively. These discoveries will help drive the development of high-performance narrowband deep-blue emitters and bring about a revolution in OLED industry.

Bis-tridentate Ir(III) Phosphors and Blue Hyperphosphorescence with Suppressed Efficiency Roll-Off at High Brightness

Narrowband blue emitters are indispensable in achieving ultrahigh-definition OLED displays that satisfy the stringent BT 2020 standard. Hereby, a series of bis-tridentate Ir(III) complexes bearing electron-deficient imidazo[4,5-b]pyridin-2-ylidene carbene coordination fragments and 2,6-diaryloxy pyridine ancillary groups were designed and synthesized. They exhibited deep blue emission with quantum yields of up to 89% and a radiative lifetime of 0.71 μs in the DPEPO host matrix, indicating both the high efficiency and excellent energy transfer process from the host to dopant. The OLED based on Irtb1 showed an emission at 468 nm with a maximum external quantum efficiency (EQE) of 22.7%. Moreover, the hyper-OLED with Irtb1 as a sensitizer for transferring energy to terminal emitter v-DABNA exhibited a narrowband blue emission at 472 nm and full width at half-maximum (FWHM) of 24 nm, a maximum EQE of 23.5%, and EQEs of 19.7, 16.1, and 12.9% at a practical brightness of 100, 1000, and 5000 cd/m2, respectively.