A Quadruple-Borylated Multiple-Resonance Emitter with para/meta Heteroatomic Patterns for Narrowband Orange-Red Emission

Hindered by spectral broadening issues with redshifted emission, long-wavelength (e.g., maxima beyond 570 nm) multiple resonance (MR) emitters with full width at half maxima (FWHMs) below 20 nm remain absent. Herein, by strategically embedding diverse boron (B)/nitrogen (N) atomic pairs into a polycyclic aromatic hydrocarbon (PAH) skeleton, we propose a hybrid pattern for the construction of a long-wavelength narrowband MR emitter. The proof-of-concept emitter B4N6-Me realized orange-red emission with an extremely small FWHM of 19 nm (energy unit: 70 meV), representing the narrowest FWHM among all reported long-wavelength MR emitters. Theoretical calculations revealed that the cooperation of the applied para B-π-N and para B-π-B/N-π-N patterns is complementary, which gives rise to both narrowband and redshift characteristics. The corresponding organic light-emitting diode (OLED) employing B4N6-Me achieved state-of-the-art performance, e.g., a narrowband orange-red emission with an FWHM of 27 nm (energy unit: 99 meV), an excellent maximum external quantum efficiency (EQE) of 35.8 %, and ultralow efficiency roll-off (EQE of 28.4 % at 1000 cd m⁻²). This work provides new insights into the further molecular design and synthesis of long-wavelength MR emitters.     

A Simple Molecular Design Strategy for Pure-Red Multiple Resonance Emitters

Though the flourishment of materials with multiple resonance (MR) in blue to green regions, red-emissive MR emitters are still rare in literatures, which definitely should be resolved for further applications. Herein, we report a simple molecular design strategy for the construction of pure-red MR emitters by conjugate charge transfer, which could greatly enhance the π-conjugation degree and charge-transfer property of the target molecule while maintaining the basic feature of MR, leading to a significant redshift of more than 128 nm compared to the selected parent MR core. The proof-of-concept emitter PPZ-BN exhibited a pure-red emission with a dominant peak at 613 nm and a small full-width-at-half-maximum of 0.16 eV (48 nm). The optimized organic light-emitting diode showed a high external quantum efficiency of 26.9 %, a small efficiency roll-off, and an excellent operation stability (LT99) of more than 43 hours at an initial luminance of 10 000 cd m⁻².     

Introducing Spiro-locks into the Nitrogen/Carbonyl System towards Efficient Narrowband Deep-blue Multi-resonance TADF Emitters

The current availability of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials with excellent color purity and high device efficiency in the deep-blue region is appealing. To address this issue in the emerged nitrogen/carbonyl MR-TADF system, we propose a spiro-lock strategy. By incorporating spiro functionalization into a concise molecular skeleton, a series of emitters (SFQ, SOQ, SSQ, and SSeQ) can enhance molecular rigidity, blue-shift the emission peak, narrow the emission band, increase the photoluminescence quantum yield by over 92 %, and suppress intermolecular interactions in the film state. The referent CZQ without spiro structure has a more planar skeleton, and its bluer emission in the solution state redshifts over 40 nm with serious spectrum broadening and a low PLQY in the film state. As a result, SSQ achieves an external quantum efficiency of 25.5 % with a peak at 456 nm and a small full width at half maximum of 31 nm in a simple unsensitized device, significantly outperforming CZQ. This work discloses the importance of spiro-junction in modulating deep-blue MR-TADF emitters.     

Combining Carbazole Building Blocks and ν-DABNA Heteroatom Alignment for a Double Boron-Embedded MR-TADF Emitter with Improved Performance

Building blocks and heteroatom alignments are two determining factors in designing multiple resonance (MR)-type thermally activated delayed fluorescence (TADF) emitters. Carbazole-fused MR emitters, represented by CzBN derivatives, and the heteroatom alignments of ν-DABNA are two star series of MR-TADF emitters that show impressive performances from the aspects of building blocks and heteroatom alignments, respectively. Herein, a novel CzBN analog, Π-CzBN, featuring ν-DABNA heteroatom alignment is developed via facile one-shot lithium-free borylation. Π-CzBN exhibits superior photophysical properties with a photoluminescence quantum yield close to 100 % and narrowband sky blue emission with a full width at half maximum (FWHM) of 16 nm/85 meV. It also gives efficient TADF properties with a small singlet-triplet energy offset of 40 meV and a fast reverse intersystem crossing rate of 2.9×10⁵ s⁻¹. The optimized OLED using Π-CzBN as the emitter achieves an exceptional external quantum efficiency of 39.3 % with a low efficiency roll-off of 20 % at 1000 cd m⁻² and a narrowband emission at 495 nm with FWHM of 21 nm/106 meV, making it one of the best reported devices based on MR emitters with comprehensive performance.     

Pre‐oxidation of Gold Nanoclusters Results in a 66 % Anodic Electrochemiluminescence Yield and Drives Mechanistic Insights

Gold nanoclusters (AuNCs) are attractive electrochemiluminescence (ECL) emitters because of their excellent stability, near IR emission, and biocompatibility. However, their ECL quantum yield is relatively low, and our limited fundamental understanding has hindered rational improvement of this parameter. Herein, we report drastic enhancement of the ECL of ligand‐stabilized AuNCs by on‐electrode pre‐oxidation with triethylamine (TEA) as a co‐reactant. The l ‐methionine‐stabilized AuNCs resulted in a record high ECL yield of 66 %. This strategy was successfully extended to other AuNCs, and it is more effective for ligand shells that allow more effective electron transfer. In addition, excitation of the pre‐oxidized ECL required a lower potential than conventional methods, and no additional instrument was required. This work opens avenues for solving a challenging problem of AuNC‐based ECL probes and enriches fundamental understanding, greatly broadening their potential applications.     

Regulation of Multiple Resonance Delayed Fluorescence via Through-Space Charge Transfer Excited State towards High-Efficiency and Stable Narrowband Electroluminescence

B- and N-embedded multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters usually suffer from slow reverse intersystem crossing (RISC) process and aggregation-caused emission quenching. Here, we report the design of a sandwich structure by placing the B−N MR core between two electron-donating moieties, inducing through-space charge transfer (TSCT) states. The proper adjusting of the energy levels brings about a 10-fold higher RISC rate in comparison with the parent B−N molecule. In the meantime, a high photoluminescence quantum yield of 91 % and a good color purity were maintained. Organic light-emitting diodes based on the new MR emitter achieved a maximum external quantum efficiency of 31.7 % and small roll-offs at high brightness. High device efficiencies were also obtained for a wide range of doping concentrations of up to 20 wt % thanks to the steric shielding of the B−N core. A good operational stability with LT₉₅ of 85.2 h has also been revealed. The dual steric and electronic effects resulting from the introduction of a TSCT state offer an effective molecular design to address the critical challenges of MR-TADF emitters.     

Doping Cu in semiconductor nanocrystals: some old and some new physical insights

Cu-doped inorganic semiconductors with concomitant optical properties have garnered enormous research interest in the last two decades. However, uncertainties over the origin of Cu emission, its oxidation state, resemblance with trap state emission, position of Cu d-state, emission spectral width, and moreover understanding of the doping mechanism restricted the wide development of the synthetic methodology for high-quality Cu-doped nanocrystals. It has been shown recently that the emission from Cu-doped semiconductor nanocrystals can span over a wide spectral window and could be a potential color tunable dispersed nanocrystal emitter. Herein, we report the size and composition of variable Cu-doped ZnS/Zn(1?x)Cd(x)S zinc-blende (ZB) surface alloyed nanocrystals with intense, stable, and tunable emission covering the blue to red end of the visible spectrum. Further, the Cu dopant emission is distinguished from trap state emission, and the composition variable spectral broadening has been justified on the account of a different environment around the Cu ions in the host lattice. Whereas some findings are in agreement with past reports, several new physical insights presented here would help the community for an in-depth mechanistic study on Cu doping. Moreover, these doped nanocrystal emitters can be a promising candidate for application ranging from optoelectronics to bio-labeling.     

Structural Engineering of Luminogens with High Emission Efficiency Both in Solution and in the Solid State

Developing molecules with high emission efficiency both in solution and the solid state is still a great challenge, since most organic luminogens are either aggregation‐caused quenching or aggregation‐induced emission molecules. This dilemma was overcome by integrating planar and distorted structures with long alkyl side chains to achieve DAπAD type emitters. A linear diphenyl–diacetylene core and the charge transfer effect ensure considerable planarity of these molecules in the excited state, allowing strong emission in dilute solution (quantum yield up to 98.2 %). On the other hand, intermolecular interactions of two distorted cyanostilbene units restrict molecular vibration and rotation, and long alkyl chains reduce the quenching effect of the π–π stacking to the excimer, eventually leading to strong emission in the solid state (quantum yield up to 60.7 %).     

Triptycene-Fused Sterically Shielded Multi-Resonance TADF Emitter Enables High-Efficiency Deep Blue OLEDs with Reduced Dexter Energy Transfer

Designing multi-resonance (MR) emitters that can simultaneously achieve narrowband emission and suppressed intermolecular interactions is challenging for realizing high color purity and stable blue organic light-emitting diodes (OLEDs). Herein, a sterically shielded yet extremely rigid emitter based on a triptycene-fused B,N core (Tp-DABNA) is proposed to address the issue. Tp-DABNA exhibits intense deep blue emissions with a narrow full width at half maximum (FWHM) and a high horizontal transition dipole ratio, superior to the well-known bulky emitter, t-DABNA. The rigid MR skeleton of Tp-DABNA suppresses structural relaxation in the excited state, with reduced contributions from the medium- and high-frequency vibrational modes to spectral broadening. The hyperfluorescence (HF) film composed of a sensitizer and Tp-DABNA shows reduced Dexter energy transfer compared to those of t-DABNA and DABNA-1. Notably, deep blue TADF-OLEDs with the Tp-DABNA emitter display higher external quantum efficiencies (EQE_max=24.8 %) and narrower FWHMs (≤26 nm) than t-DABNA-based OLEDs (EQE_max=19.8 %). The HF-OLEDs based on the Tp-DABNA emitter further demonstrate improved performance with an EQE_max of 28.7 % and mitigated efficiency roll-offs.     

Molecular Design Approach Managing Molecular Orbital Superposition for High Efficiency without Color Shift in Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes

Molecular design principles of thermally activated delayed fluorescent (TADF) emitters having a high quantum efficiency and a color tuning capability was investigated by synthesizing three TADF emitters with donors at different positions of a benzonitrile acceptor. The position rendering a large overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) enhances the quantum efficiency of the TADF emitter. Regarding the orbital overlap, donor attachments at 2- and 6-positions of the benzonitrile were more beneficial than 3- and 5-substitutions. Moreover, an additional attachment of a weak donor at the 4-position further increased the quantum efficiency without decreasing the emission energy. Therefore, the molecular design strategy of substituting strong donors at the positions allowing a large molecular orbital overlap and an extra weak donor is a good approach to achieve both high quantum efficiency and a slightly increased emission energy.     

态定(线性响应)-极化连续模型/含时密度泛函方法研究一种有机发光材料的吸收和发射光谱

3-(二氰亚甲基)-5,5-二甲基-1-(3-[9-(2-乙基-己基)-咔唑基]-乙烯基)环己烷(DCDHCC)是一种用于光电器件中的有机染料,它具有良好的发光特性.我们使用含时密度泛函方法(TD-PBE0,TD-BMK和TD-M06)以及极化连续模型(PCM)计算了该材料在溶剂中的吸收和发射特性.计算中使用了线性响应(LR)、态定(SS)两种溶剂模型和6-31G(d)、6-31+G(d,p)两种基组.计算了DCDHCC在苯、四氢呋喃和丙酮溶剂中的吸收和发射光谱,并与实验观测进行了比较.结果表明:对于吸收光谱的计算,杂化函数的影响大于基组和溶剂模型,在三种函数中BMK更适于研究DCDHCC的吸收光谱;而对于发射光谱,基组的影响最大,基组通过影响激发态构型从而影响发射光谱,对于激发态构型的优化需要使用6-31+G(d,p)基组.我们希望这些研究能对今后设计类似的发光分子有帮助.     

Introduction of a hydroxy group at the para position and N-iodophenylation of N-arylamides using phenyliodine(III) bis(trifluoroacetate)

The reaction of anilides with phenyliodine(III) bis(trifluoroacetate) (PIFA) in trifluoroacetic acid (TFA), TFA-CHCl3, or hexafluoroisopropyl alcohol (HFIP) is described. When the acyl group of the anilide is highly electronegative, such as trifluoroacetyl, or the phenyl group is substituted with an electron-withdrawing group, the 4-iodophenyl group is transferred from PIFA to the amide nitrogen to afford acetyldiarylamines. On the other hand, when the acyl group contains an electron-donating function, such as 4-methoxyphenyl, or the phenyl group is substituted with an electron-donating group, a trifluoroacetoxy group is transferred to the para position of the anilide aromatic ring. This group is hydrolyzed during workup to produce the corresponding phenol.     

Constructing Charge-Transfer Excited States Based on Frontier Molecular Orbital Engineering: Narrowband Green Electroluminescence with High Color Purity and Efficiency

The design and synthesis of organic materials with a narrow emission band in the longer wavelength region beyond 510 nm remain a great challenge. For constructing narrowband green emitters, we propose a unique molecular design strategy based on frontier molecular orbital engineering (FMOE), which can integrate the advantages of a twisted donor–acceptor (D-A) structure and a multiple resonance (MR) delayed fluorescence skeleton. Attaching an auxiliary donor to a MR skeleton leads to a novel molecule with twisted D-A and MR structure characteristics. Importantly, a remarkable red-shift of the emission maximum and a narrowband spectrum are achieved simultaneously. The target molecule has been employed as an emitter to fabricate green organic light-emitting diodes (OLEDs) with Commission Internationale de L'Eclairage (CIE) coordinates of (0.23, 0.69) and a maximum external quantum efficiency (EQE) of 27.0 %.     

Frontier Molecular Orbital Engineering: Constructing Highly Efficient Narrowband Organic Electroluminescent Materials

It is of great strategic significance to develop highly efficient narrowband organic electroluminescent materials that can be utilized to manufacture ultra-high-definition (UHD) displays and meet or approach the requirements of Broadcast Television 2020 (B.T.2020) color gamut standards. This motif poses challenges for molecular design and synthesis, especially for developing generality, diversity, scalability, and robustness of molecular structures. The emergence of multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters has ingeniously solved the problems and demonstrated bright application prospects in the field of UHD displays, sparking a research boom. This Minireview summarizes the research endeavors of narrowband organic electroluminescent materials, with emphasis on the tremendous contribution of frontier molecular orbital engineering (FMOE) strategy. It combines the outstanding advantages of MR framework and donor-acceptor (D−A) structure, and can achieve red-shift and narrowband emission simultaneously, which is of great significance in the development of long-wavelength narrowband emitters with emission maxima especially exceeding 500 nm. We hope that this Minireview would provide some inspiration for what could transpire in the future.     

Constructing Charge‐Transfer Excited States Based on Frontier Molecular Orbital Engineering: Narrowband Green Electroluminescence with High Color Purity and Efficiency

The design and synthesis of organic materials with a narrow emission band in the longer wavelength region beyond 510 nm remain a great challenge. For constructing narrowband green emitters, we propose a unique molecular design strategy based on frontier molecular orbital engineering (FMOE), which can integrate the advantages of a twisted donor–acceptor (D‐A) structure and a multiple resonance (MR) delayed fluorescence skeleton. Attaching an auxiliary donor to a MR skeleton leads to a novel molecule with twisted D‐A and MR structure characteristics. Importantly, a remarkable red‐shift of the emission maximum and a narrowband spectrum are achieved simultaneously. The target molecule has been employed as an emitter to fabricate green organic light‐emitting diodes (OLEDs) with Commission Internationale de L'Eclairage (CIE) coordinates of (0.23, 0.69) and a maximum external quantum efficiency (EQE) of 27.0 %.     

The influence of chloro-substituent sites of hexachlorobiphenyl on the respiration of rat liver mitochondria.

The actions of three hexachlorobiphenyls (HCBs) 2,3,4,2',3',4'-, 2,3,4,3',4',5'- and 3,4,5,3',4',5'-HCBs, on the respiration of rat liver mitochondria with succinate as the substrate were compared, and the effect of chloro-substitution sites in HCB on the respiration was examined. 2,3,4,2',3',4'-HCB strongly inhibited both state 3 and 2,4-dinitrophenol (DNP)-stimulated respiration with 50% inhibition dose of 52 and 54 microM for state 3 and DNP-stimulated respiration, respectively. The inhibitory action of 2,3,4,3',4',5'-HCB on both respiration was approximately half as potent as that of 2,3,4,2',3',4'-HCB. On the other hand, 3,4,5,3',4',5'-HCB did not inhibit any respiration at all. These results indicate that both inside (ortho) and outside (meta or para) positions in each phenyl ring of the biphenyl molecule should be replaced with chlorines for HCB to be an effective inhibitor. Either the actual position of chloro-substituent or steric conformation caused by its substitution or both can be considered as factors affecting the inhibition. On the basis of the conformational energy, calculated by AM1 (Austin model 1) method, with increases in chlorine number in ortho position, HCB molecule became angulated. Furthermore, calculated probability of the conformation distribution for HCB indicated that the probability of nonplanarity was higher for effective HCB than for less effective HCB. These structural features suggest the significance of steric conformation as well as chloro-substituent sites in determining the inhibitory ability of HCB.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modified spontaneous emissions of europium complex in weak PMMA opals

Engineering spontaneous emission by means of photonic crystals (PHC) is under extensive study. However PHC modification of line emissions of rare earth (RE) ions has not been thoroughly understood, especially in cases of weak opal PHCs and while emitters are well dispersed into dielectric media. In this study, poly-methyl methacrylate (PMMA) opal PHCs containing uniformly dispersed europium chelate were fabricated with finely controlled photonic stop band (PSB) positions. Measurements of luminescent dynamics and angle resolved/integrated emission spectra as well as numerical calculations of total densities of states (DOS) were performed. We determined that in weak opals, the total spontaneous emission rate (SER) of Σ(5)D(0)-(7)F(J) for Eu(3+) was independent of PSB positions but was higher than that of the disordered powder sample, which was attributed to higher effective refractive indices in the PHC rather than PSB effect. Branch SER of (5)D(0)-(7)F(2) for Eu(3+) in the PHCs, on the other hand, was spatially redistributed, suppressed or enhanced in directions of elevated or reduced optical modes, keeping the angle-integrated total unchanged. All the results are in agreement with total DOS approximation. Our paper addressed two unstudied issues regarding modified narrow line emission in weak opal PHCs: firstly whether PSB could change the SER of emitters and whether there exist, apart from PSB, other reasons to change SERs; secondly, while directional enhancement and suppression by PSB has been confirmed, whether the angle-integrated overall effect is enhancing or suppressing.     

Investigation of selective mono-deallylation of O,O'-diallylcatechols and 3-methylene-1,5-benzodioxepanes

Selective mono-deallylation of O,O'-diallylcatechols using 10% Pd/C was investigated to give the correspond-ing allylphenols. A similar reaction of 3-methylene-1,5-benzodioxepanes afforded O-methacryl catecohols. When substrates bearing various substituents on the benzene ring were subjected to the reaction, regioselective cleavage of an ether bond occurred at the side of para position to an electron-withdrawing group on the aromatic ring. On the other hand, an electron-donating group did not cause any selectivity.     

Acridin-9(10H)-one-based blue thermally activated delayed fluorescence materials: improvement of color purity and efficiency stability

A series of donor-acceptor-donor (D-A-D) type blue thermally activated delayed fluorescence (TADF) emitters, namely, 2,7-DtBuCz-AD, 3,6-DtBuCz-AD, 3,6-DMAC-AD, and 3,6-DMAC-AD-CF₃, were developed with highly rigid acridin-9(10H)-one (i.e. acridone [AD]) as acceptor. The regioisomeric effect study revealed that the attachment of donors at 3,6-sites of AD ring dramatically enhanced TADF ratio in comparison with the 2,7-site isomer. On the one hand, by varying donors from dimethylacridine (DMAC) to tert-butylcarbazole (tBuCz) at 3,6-sites of AD ring, the emission color purity of blue TADF emitters was improved from sky blue to deep blue. On the other hand, by introducing trifluoromethyl (CF₃) onto 9-site phenyl ring of 3,6-DtBuCz-AD, the efficiency stability of the sky blue emission for 3,6-DMAC-AD-CF₃ was remarkably improved. The deep blue organic light-emitting diode (OLED) of 3,6-DtBuCz-AD exhibited a maximum external quantum efficiency (EQE_max) of 17.88% with CIE coordinates of (0.15, 0.08), which is among the best performances ever reported for deep blue TADF-OLEDs. The sky-blue OLED of 3,6-DMAC-AD realized an EQE_max of 23.16%. And with the incorporation of CF₃, the sky blue device of 3,6-DMAC-AD-CF₃ exhibited extremely low efficiency loss of only 5.1% at the high brightness of 1,000 cd/m².     

A Single-Enantiomer Emitter Enabled Superstructural Helix Inversion for Upconverting and Downshifting Luminescence with Bidirectional Circular Polarization

The helical twisting tendency of liquid crystals (LCs) is generally governed by the inherent configuration of the chiral emitter. Here, we introduce the multistage inversion of supramolecular chirality as well as circularly polarized luminescence (CPL) by manipulating the ratio of single enantiomeric emitters (R-PCP) to LC monomers (5CB). Increasing the content of R-PCP from 1 wt % to 3 wt % inverted the helix of LCs from left-handed to right-handed, accompanying a CPL sign changed from positive to negative. The biaxiality of chiral emitters, as well as the steric effect of chiral-chiral and chiral-achiral interaction, were identified as the reasons for helical sense inversion. Due to the strong helical twisting power, 4 wt % R-PCP drove the photonic band gap (PBG) of chiral LCs to match up with their emission range, leading to an inversion of the CPL again with a high dissymmetry factor (≈1.2). Directly adjusting the PBG using chiral emitters is seldom achieved in cholesteric LCs. On this basis, an achiral sensitizer PtTPBP was assembled into the helical superstructure. The generation of triplet-triplet annihilation-induced upconverted CPL from R-PCP and the downshifting CPL from PtTPBP with opposite rotation was achieved in a single chiral LC system by tuning the position of the PBG.