Highly efficient non-doped blue fluorescent OLEDs with low efficiency roll-off based on hybridized local and charge transfer excited state emitters

Tuning Molecular Packing and Boosting Self-Assembling Properties via Ring Fusion Strategy in Naphthalimide-Based A-D-A Conjugated Systems

Two fully fused acceptor-donor-acceptor (A-D-A) architecture conjugated derivatives (NPF and NCF) comprising an electron-withdrawing naphthalimide (NMI) and two different electron-donating cores, phenanthrene and carbazole, respectively, were conveniently synthesized by bismuth(III)-catalyzed selective cyclization of vinyl ethers. Compared with their corresponding single bond-linked A-D-A molecules NPS and NCS, both having a moderately twisted aromatic configuration, the ring fusion strategy leads to fully coplanar conjugated skeletons and greatly changes the electronic structures, photophysical properties, self-assembling behaviors, and molecular packing motifs. In particular, the naphthalimide/carbazole derivative NCF exhibits intriguing 2D brickwork packing and significantly enhanced self-assembling properties.

Thermally Activated Delayed Fluorescence with Nanosecond Emission Lifetimes and Minor Concentration Quenching: Achieving High-Performance Nondoped and Doped Blue OLEDs

Simultaneously achieving a high photoluminescence quantum yield (PLQY), ultrashort exciton lifetime, and suppressed concentration quenching in thermally activated delayed fluorescence (TADF) materials is desirable yet challenging. Here, a novel acceptor-donor-acceptor type TADF emitter, namely, 2BO-sQA, wherein two oxygen-bridged triarylboron (BO) acceptors are arranged with cofacial alignment and positioned nearly orthogonal to the rigid dispirofluorene-quinolinoacridine (sQA) donor is reported. This molecular design enables the compound to achieve highly efficient (PLQYs up to 99%) and short-lived (nanosecond-scale) blue TADF with effectively suppressed concentration quenching in films. Consequently, the doped organic light-emitting diodes (OLEDs) base on 2BO-sQA achieve exceptional electroluminescence performance across a broad range of doping concentrations, maintaining maximum external quantum efficiencies (EQEs) at over 30% for doping concentrations ranging from 10 to 70 wt%. Remarkably, the nondoped blue OLED achieves a record-high maximum EQE of 26.6% with a small efficiency roll-off of 14.0% at 1000 candelas per square meter. By using 2BO-sQA as the sensitizer for the multiresonance TADF emitter ν-DABNA, TADF-sensitized fluorescence OLEDs achieve high-efficiency deep-blue emission. These results demonstrate the feasibility of this molecular design in developing TADF emitters with high efficiency, ultrashort exciton lifetime, and minimal concentration quenching.

Robust luminogens as cutting-edge tools for efficient light emission in recent decades

Blue luminogens play a vital role in white lighting and potential metal-free fluorescent materials and their high-lying excited states contribute to harvesting triplet excitons in devices. However, in TADF-OLEDs (ΔEST < 0.1 eV), although T1 excitons transfer to S1via RISC with 100% IQE, the longer lifetime of blue TADF suffers from efficiency roll-off (RO). In this case, hybridized local and charge transfer (HLCT) materials have attracted significant interest in lighting owing to their 100% hot exciton harvesting and enhanced efficiency. Both academics and industrialists widely use the HLCT strategy to improve the efficiency of fluorescent organic light-emitting diodes (FOLEDs) by harvesting dark triplet excitons through the RISC process. Aggregation-induced emissive materials (AIEgens) possess tight packing in the aggregation state, and twisted AIEgens with HLCT behaviour have a shortened conjugation length, inducing blue emission and making them suitable candidates for OLED applications. TTA-OLEDs are used in commercial BOLEDs because of their moderate efficiency and reasonable operation lifetime. In this review, we discuss the devices based on TTA fluorophores, TADF fluorophores, HLCT fluorophores, AIEgens and HLCT-sensitized fluorophores (HLCT-SF), which break through the statistical limitations.

Fabrication of high performance based deep-blue OLED with benzodioxin-6-amine-styryl-triphenylamine and carbazole hosts as electroluminescent materials

The present study reports synthesis of phenathroimidazole derivatives structures following donor-acceptor relation for high performance deep-blue light emitting diodes. Herein, methyl substituted benzodioxin-6-amine phenanthroimidazoles Cz-SBDPI and TPA-SBDPI derivatives that provide the blue light were designed and synthesized. These Cz-SBDPI and TPA-SBDPI show higher glass transition (Tg) temperatures of 199 and 194 °C and demonstrate enhanced thermal properties. Apart from enhanced thermal stability these compounds also exhibit superior photophysical, electrochemical and electroluminescent properties. The non-doped carbazole based device display improved electroluminescent performances than those of TPA-based devices. The strong orbital-coupling due to decreased energy barrier between Cz-SBDPI transitions result in deep blue emission with CIE-0.15, 0.06. For non-doped Cz-SBDPI device; high L (brightness):12,984 cd/m2; ηc (current efficiency): 5.9 cd/A; ηp (power efficiency): 5.7 lm/W and ηex (external quantum efficiency): 6.2% was observed. The results show that the D-A emitters can serve as simple but also as an effective approach to devise cheap electroluminescent materials that has high efficiency and can serve as OLED devices.

Thiophene derived sky-blue fluorescent probe for the selective recognition of mercuric ion through CHEQ mechanism and application in real time samples

A vibrant blue organic luminescent material with enhanced photophysical properties is in great demand for the generation of optoelectronic devices and luminescent sensors. In this context, the thiophene-benzimidazole probe TH-IMI was designed and synthesized by a simple condensation reaction. The synthesized probe has shown excellent photophysical properties like high FL intensity, a high quantum yield of 90% in the solution phase, a low optical bandgap of 2.84 eV, positive solvatochromic effect in emission spectra and Disaggregation Caused Quenching Effect (DCQE). Such a high luminescent probe was employed for the recognition of mercuric ions in the solution phase, solid state detection, and in tracking mercury in green gram sprouts. UV-visible absorption and emission spectra, 1H NMR titration, IR spectroscopic and ESI-MS techniques confirmed that the probe underwent a fluorescence quenching response via the CHEQ effect upon exposure to Hg2+. The stoichiometry was found to be 1:1 through Job's plot and has a fast response rate and relatively low limit of detection of about 6.13 × 10-11 M in a linear range between 0 and 110 µL.

Theoretical Research and Photodynamic Simulation of Aggregation-Induced Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

The discovery and utilization of pure organic thermally activated delayed fluorescence (TADF) materials provide a major breakthrough in obtaining high-performance and low-cost organic light-emitting diodes (OLEDs). In spite of recent research progress in TADF emitters, highly efficient and stable TADF emitters in high-concentration solutions and in the solid state have been rarely reported, and most of them suffer from aggregation-induced quenching (ACQ). To resolve this issue, the aggregation-induced delayed fluorescence (AIDF) mechanism was studied in depth by the simulation of excited-state dynamic processes, and the effect of geometric modifications on optical properties was minutely investigated based on molecular modeling. TD-DFT calculations demonstrate that it is the key point for the transformation between prompt fluorescence and TADF to effectively regulate singlet-triplet energy difference and electron-vibration coupling by the aggregation effect. Then, excellent green and red TADF materials with very small singlet-triplet energy differences of 0.05 and 0.06 eV, high TADF quantum yields up to 57.53% and 39.19%, and suitable fluorescence lifetimes of 0.99 and 1.67 us, respectively, were designed and obtained, which demonstrate the potential application of these two TADF materials in OLEDs.

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.

O,S-Acetals in a New Modification of oxo-Friedel-Crafts-Bradsher Cyclization-Synthesis of Fluorescent (Hetero)acenes and Mechanistic Considerations

This paper presents the use of O,S-acetals in a new modification of the oxo-Friedel-Crafts-Bradsher cyclization. In this reaction, under mild reaction conditions (25 °C), three- and four-ring fused RO-acenes (major) and/or HO(CH₂)₂S-acenes (minor) are formed, the latter products having never been observed before in this type of cyclization. In this way, two electronically different fluorophores could be obtained in a single cyclization reaction, one of them having strong electron donor properties (+M effect of alkoxy groups) and the other having donor-acceptor properties (+M and -I effects of the HO(CH₂)₂S-group, Hammett's constants). Further increasing the reaction temperature, HCl concentration or prolonging reaction time, surprisingly, yielded a 2:1 mixture of cis and trans dimeric isomers, as the only products of this cyclization. The DFT calculations confirmed a greater stability of the cis isomer compared to the trans isomer. The formation of unexpected dimeric products and HO(CH₂)₂S-acenes sheds light on the mechanism of oxo-Friedel-Crafts-Bradsher cyclization, involving competitive O/S atom protonation in strained O,S-acetals and in strain-free side groups of intermediate species.

Toward Narrowband and Efficient Blue Fluophosphors by Locking the Stretching Vibration of Indolocarbazole Skeletons

Developing efficient and color-saturated deep-blue emitting molecules with small Commission Internationale de L'Eclairage (CIE) y values is challenging and has great potential for wide-color gamut displays. Herein, we introduce an intramolecular locking strategy to restrain molecular stretching vibrations of the emission spectral broadening. By cyclizing rigid fluorenes and connecting electron-donating groups to the indolo[3,2,1-jk]-indolo[1',2',3':1,7]indolo[2,3-b]carbazole (DIDCz) framework, the in-plane swing of peripheral bonds and stretching vibrations of the indolocarbazole skeleton are restricted due to an increased steric hindrance from cyclized groups and diphenylamine auxochromophores. As a result, reorganization energies at the high-frequency region (1300-1800 cm-1) are reduced, realizing pure blue emission with a small full-width-at-half-maximum (FWHM) of 30 nm by suppressing shoulder peaks of polycyclic aromatic hydrocarbon (PAH) frameworks. The fabricated bottom-emitting organic light-emitting diode (OLED) exhibits an efficient external quantum efficiency (EQE) of 7.34% and deep-blue coordinates of (0.140, 0.105) at a high brightness of 1000 cd/m2. The FWHM of the electroluminescent spectrum is only 32 nm, which is one of the narrowest electroluminescent emissions among the reported intramolecular charge transfer fluophosphors. Our current findings provide a new molecular design strategy to conceive efficient and narrowband emitters with small reorganization energies.

High Electron Mobility Hot-Exciton Induced Delayed Fluorescent Organic Semiconductors

The development of high mobility emissive organic semiconductors is of great significance for the fabrication of miniaturized optoelectronic devices, such as organic light emitting transistors. However, great challenge exists in designing key materials, especially those who integrates triplet exciton utilization ability. Herein, dinaphthylanthracene diimides (DNADIs), with 2,6-extended anthracene donor, and 3'- or 4'-substituted naphthalene monoimide acceptors were designed and synthesized. By introducing acceptor-donor-acceptor structure, both materials show high electron mobility. Moreover, by fine-tuning of substitution sites, good integration with high solid state photoluminescence quantum yield of 26 %, high electron mobility of 0.02 cm²  V^-1  s^-1 , and the feature of hot-exciton induced delayed fluorescence were obtained in 4'-DNADI. This work opens a new avenue for developing high electron mobility emissive organic semiconductors with efficient utilization of triplet excitons.

Ultra-fast triplet-triplet-annihilation-mediated high-lying reverse intersystem crossing triggered by participation of nπ*-featured excited states

The harvesting of ‘hot’ triplet excitons through high-lying reverse intersystem crossing mechanism has emerged as a hot research issue in the field of organic light-emitting diodes. However, if high-lying reverse intersystem crossing materials lack the capability to convert ‘cold’ T1 excitons into singlet ones, the actual maximum exciton utilization efficiency would generally deviate from 100%. Herein, through comparative studies on two naphthalimide-based compounds CzNI and TPANI, we revealed that the ‘cold’ T1 excitons in high-lying reverse intersystem crossing materials can be utilized effectively through the triplet-triplet annihilation-mediated high-lying reverse intersystem crossing process if they possess certain triplet-triplet upconversion capability. Especially, quite effective triplet-triplet annihilation-mediated high-lying reverse intersystem crossing can be triggered by endowing the high-lying reverse intersystem crossing process with a 3ππ*→1nπ* character. By taking advantage of the permanent orthogonal orbital transition effect of 3ππ*→1nπ*, spin–orbit coupling matrix elements of ca. 10 cm−1 can be acquired, and hence ultra-fast mediated high-lying reverse intersystem crossing process with rate constant over 109 s−1 can be realized.

New-Fashioned Universal and Functional Host-Material from a Near-Ultraviolet Organic Emitter for High-Efficiency Organic Light-Emitting Diodes with Low Efficiency Roll-Offs

In this work, a near-ultraviolet (NUV) emitter, 2MCz-CNMCz, with hot-exciton property is designed based on a "long-short axis" strategy, which exhibits good thermal stability, bipolar carrier transport ability, and high T₁ energy level. Its nondoped NUV organic light-emitting diode (OLED) achieves a record maximum external quantum efficiency (η_ext ) of 7.76%, with a peak at 404 nm and CIE coordinates of (0.158, 0.039). The corresponding high exciton utilization efficiency (η_r ) in the electroluminescence process reveals its potential as a functional sensitizing host. As expected, the TBPe-based blue fluorescent OLED with 2MCz-CNMCz as the host material shows better efficiency and lower efficiency roll-off than that with traditional host material mCP. Meanwhile, the Ir complexes-based green/yellow/red phosphorescent OLEDs with 2MCz-CNMCz host are also fabricated, reaching high η_ext values of 26.1%, 30.4%, and 20.4%, respectively, and displaying negligible efficiency roll-offs at 1000 cd m^-2 , which are among the best OLED performances based on the same emitters. To the authors' best knowledge, this is the first report on the design of high-quality universal and functional host material, and may bring new inspiration to the preparation of high-efficiency, low roll-off, full-color OLEDs.

Luminescent columnar discotics as highly efficient emitters in pure deep-blue OLEDs with an external quantum efficiency of 4.7

Development of materials that serve as efficient blue emitters in solution-processable OLEDs is challenging. In this study, we report three derivatives of C₃-symmetric 1,3,5-tris(thien-2-yl)benzene-based highly luminescent room temperature columnar discotic liquid crystals (DLCs) suitable as solid-state emitters in OLED devices. When employed in solution-processed OLEDs, one of the derivatives having the highest photoluminescence quantum yield exhibited a maximum EQE of 4.7% and CIE chromaticity of (0.16, 0.05) corresponding to the ultra deep-blue emission. The finding is sufficiently significant in the field of DLC-based deep blue emitters.

One-step synthesis of indolizino[3,4,5-ab]isoindoles by manganese(I)-catalyzed C-H activation: structural studies and photophysical properties

Herein, a regioselective synthesis of indolizino[3,4,5-ab]isoindoles, a valuable class of heterocycles with interesting luminescence properties, is described using manganese(I)-catalyzed C-H activation. The reported transformation proceeds in one-step and employs readily available 2-phenylpyridines as starting materials. Furthermore, the obtained single products exhibit blue-greenish fluorescence with high quantum yields.

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.

Benzothiadiazole-based fluorophores as efficient non-doped emitters for solution-processed organic light-emitting diodes

New HLCT fluorophores are synthesized and successfully applied as non-doped emissive layers in solution-processed double-layered OLEDs. These devices exhibit intense yellow-green emission colors with superior performance.

Asymmetrical-Dendronized TADF Emitters for Efficient Non-doped Solution-Processed OLEDs by Eliminating Degenerate Excited States and Creating Solely Thermal Equilibrium Routes

The mechanism of thermally activated delayed fluorescence (TADF) in dendrimers is not clear. We report that fully‐conjugated or fully‐nonconjugated structures cause unwanted degenerate excited states due to multiple identical dendrons, which limit their TADF efficiency. We have synthesized asymmetrical “half‐dendronized” and “half‐dendronized‐half‐encapsulated” emitters. By eliminating degenerate excited states, the triplet locally excited state is ≥0.3 eV above the lowest triplet charge‐transfer state, assuring a solely thermal equilibrium route for an effective spin‐flip process. The isolated encapsulating tricarbazole unit can protect the TADF unit, reducing nonradiative decay and enhancing TADF performance. Non‐doped solution‐processed devices reach a high external quantum efficiency (EQE_max) of 24.0 % (65.9 cd A⁻¹, 59.2 lm W⁻¹) with CIE coordinates of (0.24, 0.45) with a low efficiency roll‐off and EQEs of 23.6 % and 21.3 % at 100 and 500 cd m⁻².

Constructing Highly Efficient Blue OLEDs with External Quantum Efficiencies up to 7.5 % Based on Anthracene Derivatives

Acquiring desirable device performance with deep-blue color purity that fulfills practical application requirements is still a challenge. Bipolar fluorescent emitters with hybrid local and charge transfer (HLCT) state may serve to address this issue. Herein, by inserting anthracene core in the deep-blue building blocks, the authors successfully developed two highly twisted D-π-A fluorescent emitters, ICz-An-PPI and IP-An-PPI, featuring different acceptor groups. Both exhibited superb thermal stabilities, high photo luminescent quantum yields and excellent bipolar transport capabilities. The non-doped OLEDs using ICz-An-PPI and IP-An-PPI as the emitting layers showed efficient blue emission with an external quantum efficiency (EQE_max ) of 4.32 % and 5.41 %, and the CIE coordinates of (0.147, 0.180) and (0.149, 0.150), respectively. In addition, the deep blue doped device based on ICz-An-PPI was achieved with an excellent CE_max of 5.83 cd A^-1 , EQE_max of 4.6 % and the CIE coordinate of (0.148, 0.078), which is extremely close to the National Television Standards Committee (NTSC) standard. Particularly, IP-An-PPI-based doped device had better performance, with an EQE_max of 7.51 % and the CIE coordinate of (0.150, 0.118), which was very impressive among the recently reported deep-blue OLEDs with the CIE_y <0.12. Such high performance may be attributed to the hot exciton HLCT mechanism via T₇ to S₂ . Our work may provide a new approach for designing high-efficiency deep-blue materials.

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

Achieving high-efficiency deep blue emitter with CIE_y < 0.06 (CIE, Commission Internationale de L'Eclairage) and external quantum efficiency (EQE) >10% has been a long-standing challenge for traditional fluorescent materials in organic light-emitting diodes (OLEDs). Here, we report the rational design and synthesis of two new deep blue luminogens: 4-(10-(4'-(9H-carbazol-9-yl)-2,5-dimethyl-[1,1'-biphenyl]-4-yl)anthracen-9-yl)benzonitrile (2M-ph-pCzAnBzt) and 4-(10-(4-(9H-carbazol-9-yl)-2,5-dimethylphenyl)anthracen-9-yl)benzonitrile (2M-pCzAnBzt). In particular, 2M-ph-pCzAnBzt produces saturated deep blue emissions in a non-doped electroluminescent device with an exceptionally high EQE of 10.44% and CIE_x,y (0.151, 0.057). The unprecedented electroluminescent efficiency is attributed to the combined effects of higher-order reversed intersystem crossing and triplet-triplet up-conversion, which are supported by analysis of theoretical calculation, triplet sensitization experiments, as well as nanosecond transient absorption spectroscopy. This research offers a new approach to resolve the shortage of high efficiency deep blue fluorescent emitters.

Hot exciplexes in U-shaped TADF molecules with emission from locally excited states

Fast emission and high color purity are essential characteristics of modern opto-electronic devices, such as organic light emitting diodes (OLEDs). These properties are currently not met by the latest generation of thermally activated delayed fluorescence (TADF) emitters. Here, we present an approach, called "hot exciplexes" that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moieties to an anthracene bridge, yielding an exciplex with large T1 to T2 spacing. The hot exciplex model is investigated using optical spectroscopy and quantum chemical simulations. Reverse intersystem crossing is found to occur preferentially from the T3 to the S1 state within only a few nanoseconds. Application and practicality of the model are shown by fabrication of organic light-emitting diodes with up to 32 % hot exciplex contribution and low efficiency roll-off.

High-Performance Ultraviolet Organic Light-Emitting Diode Enabled by High-Lying Reverse Intersystem Crossing

Ultraviolet (UV) organic emitters that can open up applications for future organic light-emitting diodes (OLEDs) are of great value but rarely developed. Here, we report a high-quality UV emitter with hybridized local and charge-transfer (HLCT) excited state and its application in UV OLEDs. The UV emitter, 2BuCz-CNCz, shows the features of low-lying locally excited (LE) emissive state and high-lying reverse intersystem crossing (hRISC) process, which helps to balance the color purity and exciton utilization of UV OLED. Consequently, the OLED based on 2BuCz-CNCz exhibits not only a desired narrowband UV electroluminescent (EL) at 396 nm with satisfactory color purity (CIE_{x, y} =0.161, 0.031), but also a record-high maximum external quantum efficiency (EQE) of 10.79 % with small efficiency roll-off. The state-of-the-art device performance can inspire the design of UV emitters, and pave a way for the further development of high-performance UV OLEDs.

A Novel Deep Blue LE-Dominated HLCT Excited State Design Strategy and Material for OLED

Deep blue luminescent materials play a crucial role in the organic light-emitting diodes (OLEDs). In this work, a novel deep blue molecule based on hybridized local and charge-transfer (HLCT) excited state was reported with the emission wavelength of 423 nm. The OLED based on this material achieved high maximum external quantum efficiency (EQE) of 4% with good color purity. The results revealed that the locally-excited (LE)-dominated HLCT excited state had obvious advantages in short wavelength and narrow spectrum emission. What is more, the experimental and theoretical combination was used to describe the excited state characteristic and to understand photophysical property.

Efficient Red Electroluminescence From Phenanthro[9,10-d]imidazole-Naphtho[2,3-c][1,2,5]thiadiazole Donor-Acceptor Derivatives

Red emission is one of the three primary colors and is indispensable for full color displays. Fluorescent materials that can generate efficient red electroluminescence (EL) are limited and need to be developed. In this work, we report efficient red emitters based on phenanthro[9,10-d]imidazole-naphtho[2,3-c][1,2,5]thiadiazole donor-acceptor derivatives. The molecules, abbreviated as PINzP and PINzPCN, exhibited high photoluminescence quantum yield (PLQY) up to unity in doped films. They can also reach a relatively high PLQY of ∼30% in neat films. PINzP and PINzPCN were capable of generating efficient red EL in doped devices with a maximum external quantum efficiency (EQE) of 6.96% and 5.92%, respectively.

Blue organic light-emitting diodes with hybridized local and charge-transfer excited state realizing high external quantum efficiency

Donor-spacer-acceptor (D-π-A) materials CAPI and CCAPI, with hybridized local and charge transfer (HLCT) emissive states, have been synthesized. The twisting D-π-A architecture promotes the partial separation of HOMO and LUMO, leading to an enhanced % CT component, and the anthracene moiety in CAPI and CCAPI increases the conjugation length, leading to an enhanced % LE component. The non-doped device with CCAPIb shows the blue emission (450 nm) with maximum current efficiency (η c), power efficiency (η p), and external quantum efficiency (η ex) of 16.83 cd A-1, 15.32 lm W-1, and 12.0%, respectively, as well as exciton utilization efficiency (EUE) of 95% with a luminance of 32 546 cd m-2 and a roll-off efficiency of 0.53%. The new design strategy has great potential for developing high-performance blue electroluminescent materials.

Efficient white light-emitting polymers from dual thermally activated delayed fluorescence chromophores for non-doped solution processed white electroluminescent devices

Conjugated TADF copolymers comprised of two TADF molecules linked with carbazole exhibited stable pure white emission from non-doped OLEDs with CIE coordinates (0.32, 0.35), a maximum luminance efficiency of 9.13 cd A⁻¹, and a maximum EQE of 4.17%.

Piezochromism of cyanostilbene derivatives: a small structural alteration makes a big photophysical difference

We designed two HLCT-active luminophores with high PLYQs. Under high pressure, DPMO presents better sensitivity and a smaller PL wavelength redshift than TPPA due to the high PLYQs and the strong CT state.