Synthesis and Electroluminescence of a Conjugated Polymer with Thermally Activated Delayed Fluorescence

Two Birds with One Stone: Polymerized Thermally Activated Delayed Fluorescence Small Molecules

Thermally activated delayed fluorescence (TADF) polymers show a great potential in low-cost, large-area and flexible full-color flat-panel displays. One of the most promising design rules is based on TADF+Linker, where a small molecular TADF unit is bonded to each other by a simple linker. Unlike the expensive vacuum deposition for small molecules, these polymerized TADF small molecules (Poly-TADF-SMs) are capable of cost-effective solution processing. Meanwhile, the good luminescent property of small molecular TADF emitters can be well inherited by Poly-TADF-SMs so as to bridge the efficiency gap between small molecules and polymers. Herein, we will highlight the recent progress of Poly-TADF-SMs, together with emphasis on their molecular design, photophysical and electroluminescence properties.

Unveiling the In Situ and Solvent Polymerization Engineering for Highly Efficient and Flexible Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes

Thermally activated delayed fluorescence (TADF) polymer has great potential for the construction of flexible solution-processed organic light-emitting diodes (OLEDs). However, the relationship between polymerization engineering and device functions has rarely been reported. Here, two novel TADF polymers, P-Ph4CzCN and P-Ph5CzCN, with a small energy gap between the first excited singlet and triplet states (ΔE_ST; <0.16 eV) were newly developed by both solvent and in situ polymerization of a styrene component. Detailed device performance testing indicates that both polymerization strategies ensure that the TADF polymer achieves comparable high efficiencies in commonly rigid devices, and the maximum external quantum efficiencies (EQE_max) were 11.9%, 14.1%, and 16.2% for blue, green, and white OLEDs, respectively. Although in situ polymerization provides a simplified device fabrication process, which avoids the complicated synthesis and purification of the polymer, the inevitable high-temperature annealing makes it fail in a plastic substrate device. In contrast, P-Ph5CzCN achieved by solvent polymerization enables the successful fabrication of a flexible device on a poly(ethylene terephthalate) (PET) substrate, which was the first reported flexible OLED based on a TADF polymer. This work provides a strong guideline for the simple fabrication of TADF polymer devices and the application of TADF polymer materials in OLED flexible panels and flexible lighting.

Zero-Zero Energy-Dominated Degradation in Blue Organic Light-Emitting Diodes Employing Thermally Activated Delayed Fluorescence

Blue-emitting organic light-emitting diodes (OLEDs) fall significantly behind other OLEDs in operational stability. To better understand the key factors governing the stability of blue OLEDs employing thermally activated delayed fluorescence (TADF), nine efficient sky-blue to green TADF emitters with different frontier orbital energy levels and different TADF lifetimes have been designed and synthesized on the basis of charge-transfer (CT) acridine/phenyltriazine derivatives. Among them, ToDMAC-TRZ, a molecule composed of a 9,9-dimethyl-2,7-di-o-tolyl-9,10-dihydroacridine donor and a 2,4,6-triphenyl-1,3,5-triazine acceptor, shows a quantum yield of nearly 1 and a TADF lifetime as short as 0.59 μs in thin film. However, the stability of OLEDs is independent of the frontier orbital energy levels and TADF lifetime of the emitter. In contrast, the device half-life is found to decrease by five-sixths as the 0-0 energy of the singlet excitons increases by about 0.06 eV, which can be well-explained by the Arrhenius equation employing a photoreaction model. Whether in photoluminescence or electroluminescence, the contribution of long-lifetime triplet excitons to degradation is much lower than expected, which can be accounted for by how the solid-state solvation effect reduces the energy of the ³CT state and how most molecules have a low-lying locally excited triplet state.

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 (EQEmax ) 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 .

A scaffold of thermally activated delayed fluorescent polymer dots towards aqueous electrochemiluminescence and biosensing applications

Thermally activated delayed fluorescent (TADF) polymer dots were prepared, which enables aqueous electrochemiluminescence of TADF polymer emitters and its biosensor application for the first time.

Red to orange thermally activated delayed fluorescence polymers based on 2-(4-(diphenylamino)-phenyl)-9H-thioxanthen-9-one-10,10-dioxide for efficient solution-processed OLEDs

Most highly efficient thermally activated delayed fluorescence (TADF)-based organic light-emitting diodes (OLEDs) are multi-layer devices fabricated by thermal vacuum evaporation techniques, which are unfavorable for real applications. However, there are only a few reported examples of efficient solution-processed TADF OLEDs, in particular TADF polymer OLEDs. Herein, a series of solution-processable TADF conjugated polymers (PCTXO/PCTXO-Fx (x = 25, 50 and 75)) were designed and synthesized by copolymerization of 2-(4-(diphenylamino)-phenyl)-9H-thioxanthen-9-one-10,10-dioxide (TXO-TPA) as a red/orange emissive TADF unit, 9,9'-((fluorene-9,9-diyl)-bis(octane-8,1-diyl))-bis(3,6-di-tert-butylcarbazole) as host/hole-transporting unit and 2,7-N-(heptadecan-9-yl)carbazole as a conjugated linker and solubilizing group. They possessed a conjugated backbone with donor TPA-carbazole/fluorene moieties and a pendent acceptor 9H-thioxanthen-9-one-10,10-dioxide (TXO) forming a twisted donor-acceptor structure. These polymers in neat films displayed red/orange color emissions (601-655 nm) with TADF properties, proved by theory calculations and transient PL decay measurements. Their hole-transporting capability was improved when the content of 9,9'-((fluorene-9,9-diyl)-bis(octane-8,1-diyl))-bis(3,6-di-tert-butylcarbazole) within the polymers increased. All polymers were successfully employed as emitters in solution-processed OLEDs. In particular, the doped OLED fabricated with PCTXO exhibited an intense deep orange emission at 603 nm with the best electroluminescence performance (a maximum external quantum efficiency 10.44%, a maximum current efficiency of 14.97 cd A-1 and a turn-on voltage of 4.2 V).

Nanoencapsulation strategy: enabling electrochemiluminescence of thermally activated delayed fluorescence (TADF) emitters in aqueous media

A nanoencapsulation strategy is introduced to a state-of-the-art thermally activated delayed fluorescence (TADF) molecule, i.e. 4CzIPN, which ensures the achievement of air-stable, water-soluble TADF nanoparticles featuring efficient TADF property without an unsatisfactory oxygen quenching effect. Accordingly, we report here for the first time the electrochemiluminescence of TADF emitters in aqueous media.

Polymer Electrochemiluminescence Featuring Thermally Activated Delayed Fluorescence

Electrochemiluminescence (ECL) based on conjugated polymers or oligomers is persistently being pursued owing to its huge application scope ranging from ultra-sensitive bioanalysis to ultra-resolution imaging and spectroscopy. Because of the theoretical limit in radiative exciton generation yield (typically ∼25 %) of those polymers or oligomers, the corresponding ECL efficiency is still limited, which hampers its ECL performance and its related applications. Herein, we report ECL based on a thermally activated delayed fluorescence (TADF) polymer scaffold, which is characteristic of all-exciton harvesting in the ECL process, and thus potentially capable of achieving ∼100 % ECL efficiency. These desired properties of the TADF polymer ECL is attributed to a fast and efficient up-conversion process from non-radiative triplet to radiative singlet states under thermal activation, which is absent in conventional fluorescent polymers/oligomers, such as F8BT. In this study, various ECL modes, including annihilation or co-reactant mode using TPrA or S₂ O₈ ^2- as co-reactant, are confirmed for our model TADF polymer ECL system, which was different from fluorescent polymer ECL counterpart. Furthermore, solid-state ECL sensing on L-cysteine (an important marker of disease) is also evaluated by using the model TADF polymer. Ultralow detection limit in combination with high sensitivity and good specificity are achieved for this model system, indicative of a high potential of the TADF polymer scaffold for applications in the broad field of ECL.

Sky-blue thermally activated delayed fluorescence polymers by using a conjugation-confined poly(aryl ether) main chain

A series of sky-blue TADF polymers were developed by applying a bipolar poly(aryl ether) main chain, and solution-processed OLEDs with these polymers doped into the host DMAC-DP-CZ showed high external quantum efficiencies of up to 14.5%.

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%.

Recent Advances in Thermally Activated Delayed Fluorescent Polymer-Molecular Designing Strategies

Thermally activated delayed fluorescent (TADF) materials, as the third generation of organic electroluminescent materials, have many advantages over other organic light-emitting diodes (OLEDs) materials, such as 100% internal quantum efficiency, no doping of heavy metals, and avoiding the shortages of ordinary fluorescent materials and phosphorescent materials. So it is considered to be the most competitive organic light-emitting materials, and has great application prospects in the field of OLEDs. So far, small-molecule TADF materials have achieved high quantum yield and full-color range of red, green, and blue. However, TADF polymers suitable for low-cost and easily scalable solution processing are less developed, which are confined by the preparation methods and polymers designing, and there are still challenges of increasing quantum efficiency and strengthening device performance. This review mainly summarizes different synthesis strategies of TADF polymers and the latest development in the field. Special attention is focused on illustrating the designing and structure-property relationship of TADF polymers, and finally, an outlook is given for the design and application prospect of TADF polymers in the future.

Rational Design of Conjugated Small Molecules for Superior Photothermal Theranostics in the NIR-II Biowindow

Extensive recent progress has been made on the design and applications of organic photothermal agents for biomedical applications because of their excellent biocompatibility comparing with inorganic materials. One major hurdle for the further development and applications of organic photothermal agents is the rarity of high-performance materials in the second near-infrared (NIR-II) window, which allows deep tissue penetration and causes minimized side effects. Up till now, there have been few reported NIR-II-active photothermal agents and their photothermal conversion efficiencies are relatively low. Herein, optical absorption of π-conjugated small molecules from the first NIR window to the NIR-II window is precisely regulated by molecular surgery of substituting an individual atom. With this technique, the first demonstration of a conjugated oligomer (IR-SS) with an absorption peak beyond 1000 nm is presented, and its nanoparticle achieves a record-high photothermal conversion efficiency of 77% under 1064 nm excitation. The nanoparticles show a good photoacoustic response, photothermal therapeutic efficacy, and biocompatibility in vitro and in vivo. This work develops a strategy to boost the light-harvesting efficiency in the NIR-II window for cancer theranostics, offering an important step forward in advancing the design and application of NIR-II photothermal agents.

Saturated Red Electroluminescence From Thermally Activated Delayed Fluorescence Conjugated Polymers

Two sets of conjugated polymers with anthraquinone groups as pendant acceptors were designed and synthesized. The acceptor is tethered to an diphenylamine group via a phenylene bridge, constructing a thermally activated delayed fluorescence (TADF) unit, which is embedded into the polymer backbone through its donor fragment, while the backbone is composed of dibenzothiophene-S, S-dioxide and 2, 7-fluorene or 2, 7-carbazole groups. The polymers show distinct TADF characteristics, confirmed by transient photoluminescence spectra and theoretical calculations. The carbazole-based polymers exhibit shorter delay lifetimes and lower energy emission relative to the fluorene-based polymers. The non-doped organic light-emitting diodes fabricated via solution processing approach produce efficient red emissions with the wavelengths of 625-646 nm. The carbazole containing polymer with 2% molar content of the TADF unit exhibits the best maximum external quantum efficiency of 13.6% and saturated red electroluminescence with the Commission Internationale de l'Eclairage coordinates of (0.62, 0.37).

Molecular Engineering of Thermally Activated Delayed Fluorescence Emitters with Aggregation-Induced Emission via Introducing Intramolecular Hydrogen-Bonding Interactions for Efficient Solution-Processed Nondoped OLEDs

Purely organic luminescent materials concurrently exhibiting thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) features are in great demand due to their high efficiency in aggregation-state toward efficient nondoped OLEDs. Herein, a class of TADF emitters adopting phenyl(pyridyl)methanone as electron-accepting segments and di(tert-butyl)carbazole and 9,9-dimethyl-9,10-dihydroacridine (or phenoxazine) as electron-donating groups are designed and synthesized. The existence of intramolecular hydrogen bonding is conducive to minish the energy difference between a singlet and a triplet (ΔE_st), suppress nonradiative decay, and increase the luminescence efficiency. By using 3CPyM-DMAC as the emitter, the nondoped device via a solution process realize a high current efficiency (CE) and external quantum efficiency (EQE) of 35.4 cd A^-1 and 11.4%, respectively, which is superior to that of CBM-DMAC with a CE and EQE of 14.3 cd A^-1 and 6.7%. This work demonstrates a promising tactic to the establishment of TADF emitters with AIE features via introducing intramolecular hydrogen bonding.

The design, synthesis and performance of thermally activated delayed fluorescence macromolecules

The design, synthesis and performance of thermally activated delayed fluorescence macromolecules are summarized, and the typical solution-processed polymeric and dendritic emitters are also organized herein as a function of EL emission color.

Superacid-catalyzed Friedel–Crafts polyhydroxyalkylation: a straightforward method to construct sky-blue thermally activated delayed fluorescence polymers

A series of sky-blue TADF polymers were developed by Friedel–Crafts polyhydroxyalkylation for efficient solution processed OLEDs.

Synthesis and Electroluminescent Properties of Through-Space Charge Transfer Polymers Containing Acridan Donor and Triarylboron Acceptors

We report the design, synthesis and electroluminescent properties of three kinds of through-space charge transfer (TSCT) polymers consisting of non-conjugated polystyrene backbone, acridan donor and triarylboron acceptors having different substituents such as hydrogen (H), fluorine (F), and trifluoromethyl (CF₃). Owing to the weak electron interaction between acridan donor and triarylboron acceptor through non-conjugated connection, blue emission with peaks in range of 429–483 nm can be achieved for the polymers in solid-state film, accompanied with photoluminescence quantum yields of 26–53%. The resulting TSCT polymers exhibit small ΔE_ST values below 0.1 eV owing to the separated HOMO and LUMO distributions, showing thermally activated delayed fluorescence with lifetimes in range of 0.19–0.98 μs. Meanwhile, the polymers show aggregation-induced emission (AIE) effect with the emission intensity increased by up to ~33 folds from solution to aggregation state. Solution-processed organic light-emitting diodes based on the polymers containing trifluoromethyl substituent exhibit promising electroluminescent performance with maximum luminous efficiency of 20.1 cd A⁻¹ and maximum external quantum efficiency of 7.0%, indicating that they are good candidates for development of luminescent polymers.

Teaching an Old Poly(arylene ether) New Tricks: Efficient Blue Thermally Activated Delayed Fluorescence

Polymer light-emitting diodes are attractive for optoelectronic applications owing to their brightness and ease of processing. However, often metals have to be inserted to increase the luminescence efficiency, and producing blue emitters is a challenge. Here we present a strategy to make blue thermally activated delayed fluorescence (TADF) polymers by directly embedding a small molecular blue TADF emitter into a poly(aryl ether) (PAE) backbone. Thanks to the oxygen-induced negligible electronic communication between neighboring TADF fragments, its corresponding blue delayed fluorescence can be inherited by the developed polymers. These polymers are free from metal catalyst contamination and show improved thermal stability. Through device optimization, a current efficiency of 29.7 cd/A (21.2 lm/W, 13.2%) is realized together with Commission Internationale de L'Eclairage coordinates of (0.18, 0.32). The value is competitive with blue phosphorescent polymers, highlighting the importance of the PAE backbone in achieving high-performance blue delayed fluorescence at a macromolecular level.

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Directly embedding a small molecular blue TADF emitter in a poly(aryl ether) backbone

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Oxygen-induced negligible electron communication leads to blue delayed fluorescence

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The achieved device efficiency is competitive with blue phosphorescent polymers

Pyrazine-Based Blue Thermally Activated Delayed Fluorescence Materials: Combine Small Singlet-Triplet Splitting With Large Fluorescence Rate

Metal-free thermally activated delayed fluorescence (TADF) emitters have emerged as promising candidate materials for highly efficient and low-cost organic light-emitting diodes (OLEDs). Here, a novel acceptor 2-cyanopyrazine is selected for the construction of blue TADF molecules via computer-assisted molecular design. Both theoretical prediction and experimental photophysical data indicate a small S₁-T₁ energy gap (ΔE_ST) and a relative large fluorescence rate (k_F) in an o-phenylene-bridged 2-cyanopyrazine/3,6-di-tert-butylcarbazole compound (TCzPZCN). The k_F value of 3.7 × 10⁷ s⁻¹ observed in a TCzPZCN doped film is among the highest in the TADF emitters with a ΔE_ST smaller than 0.1 eV. Blue TADF emission is observed in a TCzPZCN doped film with a short TADF lifetime of 1.9 μs. The OLEDs using TCzPZCN as emitter exhibit a maximum external quantum efficiency (EQE) of 7.6% with low-efficiency roll-off. A sky-blue device containing a derivative of TCzPZCN achieves an improved EQE maximum of 12.2% by suppressing the non-radiative decay at T₁.

Achieving 20% External Quantum Efficiency for Fully Solution-Processed Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence Dendrimers with Flexible Chains

Actualizing high-efficiency thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs) with fully wet processes is of great significance to the development of purely organic electroluminescence and the application of large-area OLED displays. Herein, new strategies are proposed to develop the TADF dendrimers with tunable colors by adjusting the way of linking branches to the core and the numbers of peripheral branches. Due to an energy gradient and efficient exciton utilization in the core-dendron system, the solution-processed OLEDs with the four dendrimers 5CzBN-O-Cz, 5CzBN-O-2Cz, 5CzBN-Cz, and 5CzBN-2Cz all give rise to low turn-on voltages and great device efficiency. Notably, 5CzBN-2Cz affords record-high fully solution-processed TADF OLEDs with external quantum efficiency of above 20%, which is significantly comparable to the efficiency of TADF OLEDs based on vacuum deposition. The work offers a guideline for designing solution-processable materials, paving the way toward practical applications of large-area fully solution-processed OLEDs.

Effect of a Pendant Acceptor on Thermally Activated Delayed Fluorescence Properties of Conjugated Polymers with Backbone-Donor/Pendant-Acceptor Architecture

Three sets of conjugated polymers with backbone-donor/pendant-acceptor architectures, named PCzA3PyB, PCzAB2Py, and PCzAB3Py, are designed and synthesized. The three isomeric benzoylpyridine-based pendant acceptor groups are 6-benzoylpyridin-3-yl (3PyB), 4-((pyridin-2-yl)carbonyl)phenyl (B2Py) and 4-((pyridin-3-yl)carbonyl)phenyl (B3Py), whereas the identical backbone consists of 3,6-carbazolyl and 2,7-acridinyl rings. One acridine ring and each acceptor group constitute a definite thermally activated delayed fluorescence (TADF) unit, incorporated into the main chain of the polymers through the 2,7-position of the acridine ring with the varied content. All of the polymers display legible TADF features with a short microsecond-scale delayed lifetime (0.56-1.62 μs) and a small singlet/triplet energy gap (0.10-0.19 eV). Progressively redshifted emissions are observed in the order PCzAB3Py, PCzA3PyB, and PCzAB2Py owing to the different substitution patterns of the pyridyl group. Photoluminescence quantum yields can be improved by regulating the molar content of the TADF unit in the range 0.5-50 %. The non-doped organic light-emitting devices (OLEDs) fabricated by solution-processing technology emit yellow-green to orange light. The polymers with 5 mol % of the TADF unit exhibit excellent comprehensive electroluminescence performance, in which PCzAB2Py5 achieves a maximum external quantum efficiency (EQE) of 11.9 %, low turn-on voltage of 3.0 V, yellow emission with a wavelength of 573 nm and slow roll-off with EQE of 11.6 % at a luminance of 1000 cd m^-2 and driving voltage of 5.5 V.

Resemblances of experiment and theory on aryl substituted luminogenic polypyrazolines

Polyarylpyrazolines (PPB, PPA, PPT, PPBt) containing various aryl substituents emit light in a broad color range from orange to blue, making them suitable for optoelectronics.

Combining the qualities of carbazole and tetraphenyl silane in a desirable main chain for thermally activated delayed fluorescence polymers

A series of green TADF polymers with carbazole and a tetraphenyl silane copolymer main chain were developed for use in non-doped solution processed OLEDs.

High efficiency above 20% in polymeric thermally activated delayed fluorescent organic light-emitting diodes by a host embedded backbone structure

A highly efficient polymeric thermally activated delayed fluorescent (TADF) organic light-emitting diode was developed by synthesizing a copolymer with 9-vinylcarbazole (VCz) and TADF repeating units.

Thermally Activated Delayed Fluorescence Pendant Copolymers with Electron- and Hole-Transporting Spacers

To study the effect of hole- and electron-transporting spacers in copolymers on the thermally activated delayed fluorescence (TADF) properties and device efficiency of copolymers, two series of copolymers PCzPT-x and POPT-x have been designed and synthesized successfully. In these copolymers, 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide units give green-yellow TADF, while hole-transporting 9-(4-vinylphenyl)-9H-carbazole units or electron-transporting diphenyl(4-vinylphenyl)phosphine oxide act as spacers or hosts. Their thermal, electrochemical, photophysical, and electroluminescent properties and theoretical calculations are systematically investigated to illustrate the relationships between molecular structures and photophysical properties. By optimizing the upconversion and radiative decay rate and managing the energy transfer, a green-yellow device based on POPT-25 achieves a maximum external quantum efficiency of 5.2%, a current efficiency of 16.8 cd/A, and a power efficiency of 7.8 lm/W with CIE coordinates of (0.36, 0.50). Moreover, an external quantum efficiency of 3.5% at the practical luminescence of 100 cd/m² is obtained.

Highly Efficient TADF Polymer Electroluminescence with Reduced Efficiency Roll-off via Interfacial Exciplex Host Strategy

Solution-processed organic light-emitting diodes (s-OLED) consisting of TAPC/TmPyPB interfacial exciplex host and polymer PAPTC TADF emitter are prepared, simultaneously displaying ultralow voltages (2.50/2.91/3.51/4.91 V at luminance of 1/100/1000/1000 cd m^-2), high efficiencies (14.9%, 50.1 lm W^-1), and extremely low roll-off rates (J₅₀ of 63.16 mA cm^-2, L₅₀ of ca. 15000 cd m^-2). Such performance is distinctly higher than that of pure-PAPTC s-OLED. Compared to pure-PAPTC, the advanced emissive layer structure of TAPC:PAPTC/TmPyPB is unique in much higher PL quantum yield (79.5 vs 36.3%) and nearly 4-fold enhancement in k_RISC of the PAPTC emitter to 1.48 × 10⁷ s^-1.

Solution-processed thermally activated delayed fluorescence organic light-emitting diodes using a new polymeric emitter containing non-conjugated cyclohexane units

A new solution-processable polymeric emitter containing non-conjugated cyclohexane units was developed for high-performing TADF-OLEDs.

Blue Thermally Activated Delayed Fluorescence Polymers with Nonconjugated Backbone and Through-Space Charge Transfer Effect

We demonstrate novel molecular design for thermally activated delayed fluorescence (TADF) polymers based on a nonconjugated polyethylene backbone with through-space charge transfer effect between pendant electron donor (D) and acceptor (A) units. Different from conventional conjugated D-A polymers with through-bond charge transfer effect, the nonconjugated architecture avoids direct conjugation between D and A units, enabling blue emission. Meanwhile, spatial π-π interaction between the physically separated D and A units results in both small singlet-triplet energy splitting (0.019 eV) and high photoluminescence quantum yield (up to 60% in film state). The resulting polymer with 5 mol % acceptor unit gives efficient blue electroluminescence with Commission Internationale de l'Eclairage coordinates of (0.176, 0.269), together with a high external quantum efficiency of 12.1% and low efficiency roll-off of 4.9% (at 1000 cd m^-2), which represents the first example of blue TADF nonconjugated polymer.

Highly Efficient All-Solution-Processed Fluorescent Organic Light-Emitting Diodes Based on a Novel Self-Host Thermally Activated Delayed Fluorescence Emitter

Here, we conveniently designed and synthesized a self-host thermally activated delayed fluorescence (TADF) emitter, which can not only form a uniform thin film through wet-process, but also allow the subsequently deposition of electron transporting layer (ETL) by orthogonal solvent. By using this self-host material as emitter, the all-solution-processed multilayer TADF organic light emitting diodes (OLEDs) was successfully fabricated. The maximum current, power and external quantum efficiencies of this nondoped device are 46.3 cd A^-1, 39.3 lm W^1- and 15.5%, respectively, which are much higher than the values of all-solution-processed OLEDs based on tranditional fluorescence and even comparable to the TADF devices with vacuum-deposited ETL. Moreover, the device maintains the high efficiency of 42.9 cd A^-1 and 39.0 cd A^-1 at the luminance of 100 cd m^-2 for display and 1000 cd m^-2 for practical lighting. The high efficiency and small efficiency roll-off of the all-solution-processed fluorescent OLEDs can be attributed to the superiority of the newly designed self-host TADF emitter, which possesses the perfect electroluminescent property and sufficient solvent resistance at the same time.

Inheriting the Characteristics of TADF Small Molecule by Side-Chain Engineering Strategy to Enable Bluish-Green Polymers with High PLQYs up to 74% and External Quantum Efficiency over 16% in Light-Emitting Diodes

Thermally activated delayed fluorescence (TADF) polymers are designed and synthesized by grafting the TADF emitter to the side chain of the polycarbazole backbone. By employing these TADF polymers with large ratio of delayed fluorescence component and high photoluminescence quantum yield as the emitters, the solution-processed light-emitting diodes achieve a maximal external quantum efficiency of 16.1% at a luminance of around 100 cd m^-2 .