RESUMEN

Boron/nitrogen (B/N)-doped polycyclic aromatic hydrocarbons (PAHs) with the multiple resonance (MR) effect are promising for organic light-emitting diodes (OLEDs) because of their narrowband emission and thermally activated delayed fluorescence (TADF) characteristics. Nevertheless, exploring the variety of such emitters is challenging because of the tricky and limited synthetic protocols. Herein, we designed a novel B/N-doped PAH, L-DABNA-1, whose backbone (L-DABNA) could not be achieved via conventional routes (e.g., one-pot borylation or one-shot borylation). We successfully synthesized it through stepwise one-shot borylations with precisely introducing decorations. The unique MR backbone with intersecting DABNA substructures sharing an aniline group, avoiding any para-N-π-B motif, allows L-DABNA-1 to maintain narrowband TADF emission while significantly redshifting to the yellow-green region with a reverse intersystem crossing rate (kRISC) of 1.28 × 105 s-1. An L-DABNA-1-based OLED device achieved a maximum external quantum efficiency (EQE) of over 40% and maintained a high EQE of 36.3% at 1000 cd m-2, with a current efficiency reaching ~170 cd A-1. This work not only demonstrated the great potential of stepwise borylations in synthesizing B/N-doped PAH backbones, expanding their chemical space, but also provided a promising pathway for exploring MR-TADF emitters at longer wavelengths.

RESUMEN

Multiple resonance (MR) boron-nitrogen doped polycyclic aromatic hydrocarbons (BN-PAHs) showed compelling thermally activated delayed fluorescence (TADF), surpassing those of their hydrocarbon analogs. However, the structural variety of π-extended BN-PAHs remains narrow. In this study, we synthesized three double helical BN-doped nanographenes (BN-NGs), 2a-2c, via the π-extension of the MR core. During the formation of 2a, a nanographene with one heptagon (1a) was obtained, whereas subsequent dehydrocyclization of the [6]helicene units within 2b-2c led to heptagon structures, yielding other two BN-NGs containing double heptagons (1b-1c). These BN-NGs (2a-2c and 1a-1c) showed pronounced redshifts of 100-190 nm compared to the parent MR core while preserving the TADF characteristics and prolonging the delayed fluorescence lifetime to the millisecond level. Furthermore, the integration of heptagon ring into 1a-1c expanded the conjugation, reduced the oxidation potentials, and yielded a more flexible framework compared to those of 2a-2c. The enantiomers of 2a-2c, 1a, and 1c were resolved and their chiroptical properties were studied. Notably, 1a and 1c exhibited the increased chiroptical dissymmetry factors.

RESUMEN

Despite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π-sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π-sextets). Theoretical studies indicate that the quantity of π-sextets ultimately determines the optical bandgap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94% and horizontal dipole ratio of ~90%, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light-emitting diode shows a high external quantum efficiency of 27.3%, with only a slight decrease of 3.7% at an elevated luminance level of 100,000 cd/m2.

RESUMEN

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.

RESUMEN

A promising kind of ternary chiral co-assemblies with high PLQY, large dissymmetry factor (glum), and narrowband multi-resonance characteristics are achieved by codoped-thermal annealing treatments of achiral luminescent polymer F8BT, chiral inducers R/S-5011, and achiral FRET acceptor DBN-ICZ. The optimized co-assemblies (F8BT)0.9-(R/S-5011)0.1-(DBN-ICZ)0.005 display narrowband yellow emission with full-width half maximum (FWHM) of 37 nm, PLQY of 79%, and intense CPL signals with |glum| of up to 0.26. Meaningfully, solution-processed CP-OLEDs by using those ternary chiral co-assemblies as emitting layer are successfully fabricated, which display yellow circularly polarized electroluminescence (CPEL) with EQEmax of 4.6% and gEL of up to 0.16. The corresponding Q-factor could reach up to 7.36 × 10-3, which is the highest of all the reported CP-OLEDs. Moreover, the devices also exhibit excellent comprehensive device performance with low Von of 7.0 V, high Lmax of about 25 000 cd m-2, extremely low efficiency roll-off with EQE of 4.3% at 10 000 cd m-2, as well as narrowband EL with FWHM of only 39 nm. The proposed ternary co-assembly strategy in fabricating CP-OLED provides the possibility to achieve high comprehensive device performance such as balancing high EQE and large gEL value, as well as narrowband emission, high brightness and low efficiency roll-off simultaneously.

RESUMEN

Advanced multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters with high efficiency and color purity have emerged as a research focus in developing ultra-high-definition displays. Herein, we disclose an approach to modulate charge-transfer excited states of MR emitters via intramolecular covalent bond locking. This strategy can promote the evolution of strong intramolecular charge transfer (ICT) states into weak ICT states, ultimately narrowing the full-width at half-maximum (FWHM) of emitters. To modulate the ICT intensity, two octagonal rings are introduced to yield molecule m-DCzDAz-BNCz. Compounds m-CzDAz-BNCz and m-DCzDAz-BNCz exhibit bright light-green and green fluorescence in toluene, with emission maxima of 504 and 513 nm, and FWHMs of 28 and 34 nm, respectively. Sensitized organic light-emitting diodes (OLEDs) employing emitters m-CzDAz-BNCz and m-DCzDAz-BNCz exhibit green emission with peaks of 508 and 520 nm, Commission Internationale de L'Eclairage (CIE) coordinates of (0.12, 0.65) and (0.19, 0.69), and maximum external quantum efficiencies (EQEs) of 30.2% and 32.6%, respectively.

RESUMEN

The development of deep-blue organic light-emitting diodes (OLEDs) featuring high efficiency and narrowband emission is of great importance for ultrahigh-definition displays with wide color gamut. Herein, based on the nitrogen-embedding strategy for modifying the short range charge transfer excited state energies of multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters, we introduce one or two nitrogen atoms into the central benzene ring of a versatile boron-embedded 1,3-bis(carbazol-9-yl)benzene skeleton. This approach resulted in the stabilization of the highest occupied molecular orbital energy levels and the formation of intramolecular hydrogen bonds, and thus systematic hypsochromic shifts and narrowing spectra. In toluene solution, two heterocyclic-based MR-TADF molecules, Py-BN and Pm-BN, exhibit deep-blue emissions with high photoluminescence quantum yields of 93 % and 94 %, and narrow full width at half maximum of 14 and 13 nm, respectively. A deep-blue hyperfluorescent OLED based on Py-BN exhibited a maximum external quantum efficiency of 27.7 % and desired color purity with Commission Internationale de L'Eclairage (CIE) coordinates of (0.150, 0.052). These results demonstrate the significant potential for the development of deep blue narrowband MR-TADF emitters.

RESUMEN

Luminescent materials with narrowband emission have extraordinary significance for developing ultrahigh-definition display. B-N-containing multiple resonance thermally activated delayed fluorescence (MR-TADF) materials are strong contenders. However, their device performances pervasively encounter detrimental aggregation-caused quenching effect that is highly vulnerable to doping concentration, complicating device fabrication. Therefore, constructing highly efficient and concentration-independent MR-TADF emitters is of pragmatic importance for improving device controllability and reproducibility, simplifying manufacturing procedures, and conserving production costs. Here, by systematic arrangement of donor triphenylamine and fluorophore BNCz on distinct bridges, a spatial confinement strategy has been developed with a donor-bridge-fluorophore architecture. Structurally fine modulation and progressive evolution to construct molecular entities with congested steric hindrance effect that can suppress intermolecular interactions without substantially affecting the luminescence tone of fluorophore BNCz, resulting in highly efficient and concentration-independent narrowband emitters; through isomer engineering, two isomers BN-PCz-TPA and TPA-PCz-BN with different crystal stacking patterns are synthesized by altering the connection mode between triphenylamine and BNCz. As a result, BN-PCz-TPA-based device showcases maximum external quantum efficiency (EQE) of 36.3% with narrow full-width at half-maximum of 27 nm at 10 wt% doping concentration. Even at 20 wt% doping concentration, the maximum EQE remains at 32.5% and the emission spectrum is almost unchanged.

RESUMEN

Conjugated polymers with integrating properties of delayed fluorescence and photovoltaic responses simultaneously are scarcely reported due to the generally contradictory requirements for molecular structures to achieve the two properties. Herein, an O-B(F)←N functionalized fused unit (M) with multiple resonance features, small energy gap between lowest singlet excited state (S1) and triplet excited state (T1) (ΔEST = 0.23 eV), and delayed fluorescence (τD = 0.75 µs), is designed. Selecting three benzodithiophene (BDT) derivatives as co-units to copolymerize with M, leading to a series of O-B(F)←N embedded polymers also maintaining delayed fluorescence (τD = 0.4-0.5 µs). Moreover, p-type semiconductor characteristics are tested for these polymers with hole mobilities in the range of 10-6-10-5 cm2/Vs. Devices with obviously photovoltaic responses are prepared using these polymers as donors and Y6 as the acceptor, affording a preliminary efficiency of 5.05%. This work successfully demonstrates an effective strategy to design conjugated polymers with integrating properties of delayed fluorescence and photovoltaic performance simultaneously by introducing O-B(F)←N functional groups to polymer backbones.

Asunto(s)

RESUMEN

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.

RESUMEN

Multi-boron-embedded multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters show promise for achieving both high color-purity emission and high exciton utilization efficiency. However, their development is often impeded by a limited synthetic scope and excessive molecular weights, which challenge material acquisition and organic light-emitting diode (OLED) fabrication by vacuum deposition. Herein, we put forward a B‒N covalent bond-involved π-extension strategy via post-functionalization of MR frameworks, leading to the generation of high-order B/N-based motifs. The structurally and electronically extended π-system not only enhances molecular rigidity to narrow emission linewidth but also promotes reverse intersystem crossing to mitigate efficiency roll-off. As illustrated examples, ultra-narrowband sky-blue emitters (full-width at half-maximum as small as 8 nm in n-hexane) have been developed with multi-dimensional improvement in photophysical properties compared to their precursor emitters, which enables narrowband OLEDs with external quantum efficiencies (EQEmax) of up to 42.6%, in company with alleviated efficiency decline at high brightness, representing the best efficiency reported for single-host OLEDs. The success of these emitters highlights the effectiveness of our molecular design strategy for advanced MR-TADF emitters and confirms their extensive potential in high-performance optoelectronic devices.

RESUMEN

In this study, two novel multiple resonance (MR) emitters, DtCzBN and Cy-DtCzBN, were designed based on the well-known BCzBN structure and synthesized for narrowband solution-processed organic light-emitting diodes (OLEDs). Cy-DtCzBN possesses a dimeric V-shaped structure formed by coupling two individual DtCzBN units via a nonconjugated cyclohexane linker. When compared with DtCzBN, Cy-DtCzBN, as a medium-sized molecule, was found to maintain the optical and photophysical properties of the corresponding monomeric unit, DtCzBN, but exhibits high thermal stability, excellent solubility, and good film-forming ability. Additionally, solution-processed OLEDs were fabricated by using two sets of molecules: one set of small molecular hosts and emitters (i.e., mCP and DtCzBN) and the other set of medium-sized molecular hosts and emitters (i.e., Cy-mCP and Cy-DtCzBN). Notably, devices using medium-sized molecular hosts and emitters exhibited similar optical and photophysical properties but showed significantly improved reproducibility and thermal stability compared with those based on small molecular hosts and emitters. Our current study provides some insights into molecular design strategies for thermally stable hosts and emitters, which are highly suitable for solution-processed OLEDs.

RESUMEN

Double-borylated multiple-resonance (MR) skeletons are promising templates for high performance, while the chemical design space is relatively limited. Peripheral segments are often used to decorate/fuse MR skeletons and modulate the photophysics but they can also cause unwanted spectral broadening. Herein, a narrowband MR emitter ICzDBA by fusing an MR-featured donor segment indolocarbazole into a double-borylated MR skeleton is developed. In ICzDBA, the nitrogen atom located away from the core benzene ring can also contribute to the generation of the overall MR-featured distribution through the long-range conjugation effect, along with the other boron/nitrogen atoms on the phenyl center. Thus, ICzDBA in toluene displays a narrowband emission peaking at 507 nm with a full width at half maximum of merely 20 nm (0.09 eV). Moreover, organic light-emitting diode devices using ICzDBA emitter exhibit ultrapure green emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.27, 0.70) and a high external quantum efficiency of 32.5%. These results manifest the importance of MR characters of peripheral decorations/fusions in preserving the narrowband features of MR skeletons, which provides a solution for further expanding MR structures with well-maintained narrowband characters.

RESUMEN

Locally resonant phononic crystal (LRPC) exhibit elastic wave band gap characteristics within a specific low-frequency range, but their band gap width is relatively narrow, which has certain limitations in practical engineering applications. In order to open a lower frequency band gap and broaden the band gap range, this paper proposes a new composite multiple locally resonant phononic crystal (CMLRPC). Firstly, the band structure of the CMLRPC is calculated by using the finite element method, and then the formation mechanism of the band gap of the CMLRPC is studied by analyzing its vibration mode, and the band gap width is expanded by adjusting the size of the single primitive cell in the supercell model of the CMLRPC. Secondly, an equivalent mass-spring system model for CMLRPC is established to calculate the starting frequency and cut-off frequency of the band gap, and the calculated results are in good agreement with the finite element calculation. Finally, the frequency response function of the CMLRPC is calculated and its attenuation characteristics are analyzed. Within the band gap frequency range, the attenuation values of the CMLRPC are mostly above 20 dB, indicating a good attenuation effect. Compared with traditional LRPC, this new CMLRPC opens multiple band gaps in the frequency range of 200 Hz, with a wider band gap width and better attenuation effect. In addition, considering both the contact between single primitive cell and the adjustment of their spacing in the supercell model of the CMLRPC, lower and wider band gap can be obtained. The research results of this paper provide a new design idea and method for obtaining low-frequency band gap in LRPC, and can provide reference for the design of vibration reduction and isolation structures in the field of low-frequency vibration control.

RESUMEN

Up to now, highly efficient narrowband thermally activated delayed fluorescence (TADF) molecules constructed by oxygen-bridged boron with an enhancing multiple resonance (MR) effect have been in urgent demand for solid-state lighting and full-color displays. In this work, a novel MR-TADF molecule, BNBO, constructed by the oxygen-bridged boron unit and boron-nitrogen core skeleton as an electron-donating moiety, is successfully designed and synthesized via a facile one-step synthesis. Based on BNBO as an efficient green emitter, the organic light-emitting diode (OLED) shows a sharp emission peak of 508 nm with a full-width at half-maximum (FWHM) of 36 nm and realizes quite high peak efficiency values, including an external quantum efficiency (EQEmax) of 24.3% and a power efficiency (PEmax) of 62.3 lm/W. BNBO possesses the intramolecular charge transfer (ICT) property of donor-acceptor (D-A) materials and multiple resonance characteristics, which provide a simple strategy for narrowband oxygen-boron materials.

RESUMEN

The development of high-performance multiple resonance thermally activated delayed fluorescence (MR-TADF) materials with narrowband yellow emission is highly critical for various applications in industries, such as the automotive, aerospace, and microelectronic industries. However, the modular construction approaches to expeditiously access narrowband yellow-emitting materials is relatively rare. Here, a unique molecular design concept based on frontier molecular orbital engineering (FMOE) of aromatic donor fusion is proposed to strategically address this issue. Donor fusion is a modular approach with a "leveraging effect"; through direct polycyclization of donor attached to the MR parent core, it is facile to achieve red-shifted emission by a large margin. As a result, two representative model molecules, namely BN-Cz and BN-Cb, have been constructed successfully. The BN-Cz- and BN-Cb-based sensitized organic light-emitting diodes (OLEDs) exhibit bright yellow emission with peaks of 560 and 556 nm, full-width at half-maxima (fwhm's) of 49 and 45 nm, Commission Internationale de L'Eclairage coordinates of (0.44, 0.55) and (0.43, 0.56), and maximum external quantum efficiencies (EQEs) of 32.9% and 29.7%, respectively. The excellent optoelectronic performances render BN-Cz and BN-Cb one of the most outstanding yellow-emitting MR-TADF materials.

RESUMEN

The investigation of organic light-emitting diodes (OLEDs) and organic laser devices with thermally activated delayed fluorescence (TADF) molecules is emerging due to the potential of harnessing triplets. In this work, a boron/nitrogen multiple-resonance TADF polycyclic framework fusing carbazole units (CzBNPh) was proposed. CzBNPh exhibited a narrowband emission (<30 nm), a unity photoluminescence quantum yield, and a fast radiative rate. Consequently, CzBNPh demonstrated a low distributed feedback (DFB) lasing threshold of 0.68 µJ cm-2 . Furthermore, the stimulated emission zone of CzBNPh was effectively separated from its singlet and triplet absorption, thereby minimizing the singlet-triplet annihilation under long-pulsed excitation ranging from 20 µs to 2.5 ms. Significantly, the enhanced rigid molecular conformation, thermal stability, and photo-stability resulted in improved lasing and electroluminescence stability compared to that of 5,9-diphenyl-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (DABNA)-core. These findings indicate the potential of CzBN-core as a promising framework for achieving long-pulsed wave and electrically-pumped lasing in the future.

RESUMEN

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters with narrow emission spectra have garnered significant attention in future organic light-emitting diode (OLED) displays. However, current C=O/N-embedded MR-TADF systems still lack satisfactory performance in terms of electroluminescence bandwidths and external quantum efficiencies (EQEs). In this study, a C=O/N-embedded green MR-TADF emitter, featuring two acridone units incorporated in a sterically protected 11-ring fused core skeleton, is successfully synthesized through finely controlling the reaction selectivity. The superior combination of multiple intramolecular fusion and steric wrapping strategies in the design of the emitter not only imparts an extremely narrow emission spectrum and a high fluorescence quantum yield to the emitter but also mitigates aggregation-induced spectral broadening and fluorescence quenching. Therefore, the emitter exhibits leading green OLED performance among C=O/N-based MR-TADF systems, achieving an EQE of up to 37.2 %, a full width at half maximum of merely 0.11 eV (24 nm), and a Commission Internationale de l'Éclairage coordinate of (0.20, 0.73). This study marks a significant advance in the realization of ideal C=O/N-based MR-TADF emitters and holds profound implications for the design and synthesis of other MR-TADF systems.

RESUMEN

Helicenes exhibit substantial potential as circularly polarized luminescence (CPL) active molecules. However, their application in circularly polarized organic light-emitting diodes (CP-OLEDs) is typically hindered by the challenge of integrating both high color purity and efficient triplet-harvesting capability, particularly in the blue spectral region. Herein, a series of hetero[6]helicene-based emitters that is strategically engineered through the helical extension of a deep-blue double-boron-based multiple resonance thermally activated delayed fluorescence (MR-TADF) motif, is introduced. Importantly, the helical extension does not cause apparent structural deformation or perturb frontier molecular orbitals; thus, preserving the deep-blue emission and MR-TADF characteristics of the parent molecule. This approach also leads to reduced reorganization energy, resulting in emitters with narrower linewidth and higher photoluminescence quantum yield. Further, the helical motif enhances the racemization barrier and leads to improved CPL performance with luminescence dissymmetry factor values up to 1.5 × 10-3 . Exploiting these merits, devices incorporating the chiral dopants demonstrate deep-blue emission within the Broadcast Service Television 2020 color-gamut range, record external quantum efficiencies (EQEs) up to 29.3%, and have distinctive circularly polarized electroluminescence (CPEL) signals. Overall, the authors' findings underscore the helical extension as a promising strategy for designing narrowband chiroptical materials and advancing high-definition displays.

RESUMEN

Recently, boron (B)/nitrogen (N)-embedded polycyclic aromatic hydrocarbons (PAHs), characterized by multiple resonances (MR), have attracted significant attention owing to their remarkable features of efficient narrowband emissions with small full width at half maxima (FWHMs). However, developing ultra-narrowband pure-green emitters that comply with the Broadcast Service Television 2020 (BT2020) standard remains challenging. Precise regulation of the MR distribution regions allows simultaneously achieving the emission maximum, FWHM value, and spectral shape that satisfy the BT2020 standard. The proof-of-concept molecule TPABO-DICz exhibited ultrapure green emission with a dominant peak at 515 nm, an extremely small FWHM of 17 nm, and Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.76). The corresponding bottom-emitting organic light-emitting diode (OLED) exhibited a remarkably high CIEy value (0.74) and maximum external quantum efficiency (25.8 %). Notably, the top-emitting OLED achieved nearly BT2020 green color (CIE: 0.14, 0.79) and exhibited a state-of-the-art maximum current efficiency of 226.4 cd A-1 , thus fully confirming the effectiveness of the above strategy.