Search

Metal halide perovskites have attracted extensive attention in next-generation solid-state lighting and displays due to their fascinating optoelectronic properties. However, the toxicity of lead (Pb) impedes their practical application. Herein, we report an efficient Zn-alloyed quasi-two-dimensional (quasi-2D) pure-red perovskite light-emitting device (PeLED) by introducing zinc ions (Zn2+) into the perovskite lattice and partially substituting Pb2+. The substitution of Zn2+ is confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, grazing-incidence wide-angle X-ray scattering, and transmission electron microscopy measurements. In addition, the vacancy defect density of Pb and the halogen is reduced by the introduction of Zn2+ in the PEA2(Cs0.3MA0.7)2(ZnxPb1-x)3I10 perovskite system, which leads to a more ordered crystal orientation, compact morphology, and increased photoluminescence quantum efficiency. Benefiting from the improved photoelectric properties, a maximum EQE of 9.5% and a luminescence of 453 cd m-2 are achieved for the Zn-alloyed PeLEDs, with a maximum emission peak of 658 nm and stable electroluminescence spectra under various applied biases.

The development of white light emitting diodes (WLEDs) holds great promise for replacing traditional lighting devices due to high efficiency, low energy consumption and long lifetime. Metal-organic frameworks (MOFs) with a wide range of luminescent behaviors are ideal candidates to produce white light emission in the phosphor-converted WLEDs. Encapsulation of emissive organic dyes is a simple way to obtain luminescent MOFs. In this review, we summarize the recent progress on the design and constructions of dye encapsulated luminescent MOFs phosphors. Different strategies are highlighted where white light emitting phosphors were obtained by combining fluorescent dyes with metal ions and linkers.

Quasi-2D perovskites have long been considered to have favorable "energy funnel/cascade" structures and excellent optical properties compared with their 3D counterparts. However, most quasi-2D perovskite light-emitting diodes (PeLEDs) exhibit high external quantum efficiency (EQE) but unsatisfactory operating stability due to Auger recombination induced by high current density. Herein, a synergetic dual-additive strategy is adopted to prepare perovskite films with low defect density and high environmental stability by using 18-crown-6 and poly(ethylene glycol) methyl ether acrylate (MPEG-MAA) as the additives. The dual additives containing COC bonds can not only effectively reduce the perovskite defects but also destroy the self-aggregation of organic ligands, inducing the formation of perovskite nanocrystals with quasi-core/shell structure. After thermal annealing, the MPEG-MAA with its CC bond can be polymerized to obtain a comb-like polymer, further protecting the passivated perovskite nanocrystals against water and oxygen. Finally, state-of-the-art green PeLEDs with a normal EQE of 25.2% and a maximum EQE of 28.1% are achieved, and the operating lifetime (T50 ) of the device in air environment is over ten times increased, providing a novel and effective strategy to make high efficiency and long operating lifetime PeLEDs.

A fast radiative rate, highly suppressed nonradiation, and a short exciton lifetime are key elements for achieving efficient thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) with reduced efficiency roll-off at a high current density. Herein, four representative TADF emitters are designed and synthesized based on the combination of benzophenone (BP) or 3-benzoylpyridine (BPy3) acceptors, with dendritic 3,3″,6,6″-tetra

Iridium complexes bearing chelating cyclometalates are popular choices as dopant emitters in the fabrication of organic light-emitting diodes (OLEDs). In this contribution, we report a series of blue-emitting, bis-tridentate Ir-III complexes bearing chelates with two fused five-six-membered metallacycles, which are in sharp contrast to the traditional designs of tridentate chelates that form the alternative, fused five-five metallacycles. Five Ir-III complexes, Px-21-23, Cz-4, and Cz-5, have been synthesized that contain a coordinated dicarbene pincer chelate incorporating a methylene spacer and a dianionic chromophoric chelate possessing either a phenoxy or carbazolyl appendage to tune the coordination arrangement. All these tridentate chelates afford peripheral ligand-metal-ligand bite angles of 166-170 degrees, which are larger than the typical bite angle of 153-155 degrees observed for their five-five-coordinated tridentate counterparts, thereby leading to reduced geometrical distortion in the octahedral frameworks. Photophysical measurements and TD-DFT studies verified the inherent transition characteristics that give rise to high emission efficiency, and photodegradation experiments confirmed the improved stability in comparison with the benchmark fac-[Ir(ppy)(3)] in degassed toluene at room temperature. Phosphorescent OLED devices were also fabricated, among which the carbazolyl-functionalized emitter Cz-5 exhibited the best performance among all the studied bis-tridentate phosphors, showing a maximum external quantum efficiency (EQE(max)) of 18.7 % and CIEx,y coordinates of (0.145, 0.218), with a slightly reduced EQE of 13.7 % at 100 cd m(-2) due to efficiency roll-off.

Blue thermally activated delayed fluorescence (TADF) emitters that can simultaneously achieve high efficiency in doped and nondoped organic light-emitting diodes (OLEDs) are rarely reported. Reported here is a strategy using a tri-spiral donor for such versatile blue TADF emitters. Impressively, by simply extending the nonconjugated fragment and molecular length, aggregation-caused emission quenching (ACQ) can be greatly alleviated to achieve as high as a 90 % horizontal orientation dipole ratio and external quantum efficiencies (EQEs) of up to 33.3 % in doped and 20.0 % in nondoped sky-blue TADF-OLEDs. More fascinatingly, a high-efficiency purely organic white OLED with an outstanding EQE of up to 22.8 % was also achieved by employing TspiroS-TRZ as a blue emitter and an assistant host. This compound is the first blue TADF emitter that can simultaneously achieve high electroluminescence (EL) efficiency in doped, nondoped sky-blue, and white TADF-OLEDs.

Four novel spiro[fluorene-9,9‘-thioxanthene] core based wide-energy-gap compounds Cz-S, 2Cz-S, Cz-SO2, and 2Cz-SO2 were developed as host materials for a general thermally activated delayed fluorescence (TADF) emitter (4s, 6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN). The excited states of the sulfane-containing Cz-S and 2Cz-S are in local emission (LE) states while those of the sulfonyl-containing Cz-SO2 and 2Cz-SO2 are in charge transfer (CT) states. The device based on 2Cz-S exhibits the highest efficiency among them with a maximal current efficiency (CE) of 52.1 cd/A and a maximal external quantum efficiency (EQE) of 16.5% due to the largest radiative triplet exciton utilization capacity through intersystem crossing from T1 to S1. In addition, the devices based on Cz-SO2 and 2Cz-SO2 exhibit obviously reduced efficiency roll-off due to their improved carrier balance in a wide current density range, and their J0 (the current density at the half maximum of the EQE) values reach as high as 93 and 115 mA/cm2. It is also of interest their EL spectra are independent on the host dipole moment due to the spiro-conformation that may reduce the interaction between host and dopant.

Deep-red/near-infrared (DR/NIR) OLEDs based on transition metal complexes have drawn much attention due to their potential applications in displays, bioimaging and photodynamic therapy. In this article, two novel iridium(III) complexes, (DBPz-11,12-DO)2Ir(acac) and (PPz-11,12-DO)2Ir(acac), were primarily designed and synthesized using highly rigid fused-heterocyclic phenazine derivatives as ligands. By tuning the benzo number in the phenazine, the iridium complexes exhibited significantly different emission characteristics. Strong NIR emission at 732 nm with a quantum efficiency of 13% and a lifetime of 0.60 μs was observed in the (PPz-11,12-DO)2Ir(acac) solution. In contrast, a remarkably blue-shifted DR emission at 685 nm with a quantum efficiency of 27% and a lifetime of 0.40 μs was exhibited in the (DBPz-11,12-DO)2Ir(acac) solution. As a result, both iridium complexes exhibited high-efficiency DR/NIR electroluminescence in their doped polymer light-emitting devices. The (PPz-11,12-DO)2Ir(acac) devices showed a maximum external quantum efficiency (EQE) of 4.14% with a radiance of up to 20 981 mW Sr−1 m−2, and the (DBPz-11,12-DO)2Ir(acac) devices afford an increased EQE of 7.04% with a radiance of 33 671 mW Sr−1 m−2. This strategy of using rigid fused-heterocyclic cyclometalated ligands has opened a new avenue for high-efficiency DR/NIR-emitting iridium complexes.

The effect of boronic ester substitution on the room-temperature phosphorescence properties of phenoxathiine-based derivatives was thoroughly investigated. A significantly improved phosphorescence quantum efficiency of up to 20% in the crystalline state was achieved by delicate molecular manipulation for both enhanced spin-orbital coupling and compact intermolecular packing.

Solution-processed lead halide perovskite quantum dots (QDs) are emerging as one of the most promising candidates for emissive display application. Although perovskite QDs with a full spectrum of visible light emissions have been realized for years, realizing the efficient electroluminescence of blue perovskites at room temperature still faces severe challenges. Herein, we demonstrate both the efficient photoluminescence and electroluminescence of the blue perovskite QDs via a simple FABr-modified multi-cation hot-injection (FMMHI) method. The FMMHI method is unique in both the addition of FABr into the PbBr2 precursor solution and the incorporation of small rubidium (Rb+) into the blue perovskite QDs light-emitting diodes (QLEDs). The addition of FABr into the precursor solution can realize strong quantum confinement effect, large exciton binding energy and high-quality perovskite QD films. Besides, the bandgap can be enlarged by the Rb+-induced perovskite octahedral distortion and strong quantum confinement effect. Excellent PLQYs of 64.5% and 49.8% were achieved for the developed greenish-blue QDs (Rb0.33Cs0.67)0.42FA0.58PbBr3 and deep-blue QDs (Rb0.33Cs0.67)0.42FA0.58PbCl1.25Br1.75 in solid film state. Moreover, maximum external quantum efficiencies (EQEs) of 3.6% and 0.61% were also achieved with an electroluminescence peak wavelength at 502 and 466 nm, respectively, indicating that the perovskite QDs incorporated with Rb+ possess great potential for the development of high-performance blue perovskite electroluminescence diodes.

A severe efficiency roll-off at high luminance in organic light-emitting diodes (OLEDs) generally results from a long exciton lifetime or an inappropriate device structure. The design strategy of the device plays a central role in realizing the inherent maximum potential of a specific emitter with an intrinsic photoluminescence quantum yield (PLQY) in an OLED via facilitating carrier injection, transport, and exciton confinement for efficient light emission. In this work, a yellow thermally activated delayed fluorescence (TADF) emitter, tri-PXZ-TRZ with a high PLQY and a short exciton lifetime is systematically investigated for its utilization in OLEDs. Judicious selection of suitable materials with higher energy offsets for the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and triplet excitons as well as balanced carrier injection led to the realization of highly efficient OLEDs. The maximum external quantum efficiency (EQE) of the fabricated OLEDs with tri-PXZ-TRZ as the emitter is improved from 13.3% to 21.0% via rational device engineering. Upon achieving an effective balance between the efficiency and the corresponding roll-off, the EQE was found to be retained at >10% even at a super high luminance of 60 000 cd m−2. Our results demonstrate that TADF emitter based OLEDs with well-designed device configurations could be promising for future low-cost and large-scale applications at high luminance.

Two new donor-acceptor-donor (D-A-D) small molecules, named L1 and L2, based on furan-fused and fluorinated furan-fused 1,10-phenanthroline as electron-acceptor units and 4-(bis(4-methoxyphenyl)amino)phenyl as electron-donor units, were designed and synthesized. The photophysical and electrochemical properties were studied. The results are compared and discussed with respect to the influence of attached fluorine and solvent polarity. L1 and L2 emit intense blue light in non-polar solvent with high photoluminescence (PL) quantum yield (ηPL) of 1 for L2. The absorption and PL spectra of L2 with attached fluorine atoms are red-shifted compared with those of L1. Red shifts of PL maxima are observed with the increasing solvent polarity in solution spectra for both L1 and L2. ηPL values in solutions decrease as solvent polarity increases and the ηPL difference for L1 and L2 in solution is not so pronounced as for L1 and L2 thin films. In addition, the effect of protonation on the nitrogen atoms of phenanthroline in thin films is shown. L1 and L2 were tested in the light-emitting devices and their electroluminescent properties are also reported. The preliminary results show L1 and L2 are almost pure white emitter and greenish blue emitter, respectively.

The host–guest doping system has aroused great attention due to its promising advantage in stimulating bright and persistent room-temperature phosphorescence (RTP). Currently, exploration of the explicit structure–property relationship of bicomponent systems has encountered obstacles. In this work, two sets of heterocyclic isomers showing promising RTP emissions in the solid state were designed and synthesized. By encapsulating these phosphors into a robust phosphorus-containing host, several host–guest cocrystalline systems were further developed, achieving highly efficient RTP performance with a phosphorescence quantum efficiency (ϕP) of ∼26% and lifetime (τP) of ∼32 ms. Detailed photophysical characterization and molecular dynamics (MD) simulation were conducted to reveal the structure–property relationships in such bicomponent systems. It was verified that other than restricting the molecular configuration, the host matrix could also dilute the guest to avoid concentration quenching and provide an external heavy atom effect for the population of triplet excitons, thus boosting the RTP performance of the guest., Several host–guest cocrystal systems with bright and persistent room-temperature phosphorescence were developed by utilizing a phosphorus-containing material as a robust host and newly developed isomeric organic phosphors as guests.

Sila-molecules have recently attracted attention due to their promising applications in medical and industrial fields. Compared with all-carbon parent compounds, the different covalent radius and electronegativity of silicon from carbon generally endow the corresponding sila-analogs with unique biological activity and physicochemical properties. Vinylsilanes feature both silyl-hyperconjugation effect and versatile reactivities, developing vinylsilane-based Smiles rearrangement will therefore provide an efficient platform to assemble complex silacycles. Here we report a practical Ir(III)-catalyzed cycloaromatization of ortho-alkynylaryl vinylsilanes with arylsulfonyl azides for delivering naphthyl-fused benzosiloles under visible-light photoredox conditions. The combination of experiments and density functional theory (DFT) energy profiles reveals the reaction mechanism involving α-silyl radical Smiles rearrangement., Arene-fused siloles have attracted interest due to their promising applications in electronic and optoelectronic devices. Here, the authors report Ir(III)-catalyzed cycloaromatization of ortho-alkynylaryl vinylsilanes with arylsulfonyl azides via α-silyl radical Smiles rearrangement for accessing naphthyl-fused benzosiloles under visible-light photoredox conditions.

Strategies for developing purely organic materials exhibiting both high efficiency and persistent room-temperature phosphorescence (RTP) have remained ambiguous and challenging. Herein, we propose that introducing an intermediate charge transfer (CT) state into the donor-acceptor binary molecular system holds promise for accomplishing this goal. Guest materials showing gradient ionization potentials were selected to fine-tune the intermolecularly formed CT state when doped into the same host material with a large electron affiliation potential. Such a CT intermediate state accelerates the population of the triplet exciton to benefit phosphorescent emission and decreases the phosphorescence lifetime via quenching the long-lived triplet excitons. As a result, a "trade-off" between a long phosphorescence lifetime (595 ms) and a high phosphorescent quantum yield (27.5%) can be obtained by tuning the host-guest energy gap offset. This finding highlights the key role of CT in RTP emission and provides new guidance for developing novel RTP systems.

Thermally activated delayed fluorescence (TADF) emitters with a spiral donor show tremendous potential toward high-level efficient blue organic light-emitting diodes (OLEDs). However, the underlying design strategy of the spiral donor used for blue TADF emitters remains unclear. As a consequence, researchers often do "try and error" work in the development of new functional spiral donor fragments, making it slow and inefficient. Herein, we demonstrate that the energy level relationships between the spiral donor and the luminophore lead to a significant effect on the photoluminescent quantum yields (PLQYs) of the target materials. In addition, a method involving quantum chemistry simulations that can accurately predict the aforementioned energy level relationships by simulating the spin density distributions of the triplet excited states of the spiral donor and corresponding TADF emitters and the triplet excited natural transition orbitals of the TADF emitters is established. Moreover, it also revealed that the steric hindrance in this series of molecules can form a nearly unchanged singlet (S1) state geometry, leading to a reduced nonradiative decay and high PLQY, while a moderated donor-acceptor (D-A) torsion in the triplet (T1) state can induce a strong vibronic coupling between the charge-transfer triplet (3CT) state and the local triplet (3LE) state, achieving an effective reverse intersystem crossing (RISC) process. Furthermore, an electric-magnetic coupling is formed between the high-lying 3LE state and the charge-transfer singlet (1CT) state, which may open another RISC channel. Remarkably, in company with the optimized molecular structure and energy alignment, the pivotal TADF emitter DspiroS-TRZ achieved 99.9% PLQY, an external quantum efficiency (EQE) of 38.4%, which is the highest among all blue TADF emitters reported to date.

Multifunctional luminescent materials with aggregation-induced delayed fluorescence (AIDF) are capable of suppressing concentration-caused emission quenching and exciton annihilation when used as organic light-emitting diode (OLED) emitters. In this contribution, three stimuli-responsive AIDF luminogens

Dinuclear Pt(III) complexes were commonly reported to have short-lived lowest-lying triplet states, resulting in extremely weak or no photoluminescence. To overcome this obstacle, a new series of dinuclear Pt(III) complexes, named Pt2a-Pt2c, were strategically designed and synthesized using donor (D)-acceptor (A)-type oxadiazole-thiol chelates as bridging ligands. These dinuclear Pt(III) complexes possess a d7-d7 electronic configuration and exhibit intense phosphorescence under ambient conditions. Among them, Pt2a exhibits orange phosphorescence maximized at 618 nm in degassed dichloromethane solution (Φp ≈ 8.2%, τp ≈ 0.10 μs) and near-infrared (NIR) emission at 749 nm (Φp ≈ 10.1% τp ≈ 0.66 μs) in the crystalline powder and at 704 nm (Φp ≈ 33.1%, τp ≈ 0.34 μs) in the spin-coated neat film. An emission blue-shifted by more than 3343 cm-1 is observed under mechanically ground crystalline Pt2a, affirming intermolecular interactions in the solid states. Time-dependent density functional theory (TD-DFT) discloses the lowest-lying electronic transition of Pt2a-Pt2c complexes to be a bridging ligand-metal-metal charge transfer (LMMCT) transition. The long-lived triplet states of these dinuclear platinum(III) complexes may find potential use in lighting. Employing Pt2a as an emitter, high-performance organic light-emitting diodes (OLEDs) were fabricated with NIR emission at 716 nm (η = 5.1%), red emission at 614 nm (η = 8.7%), and white-light emission (η = 11.6%) in nondoped, doped (in mCP), and hybrid (in CzACSF) devices, respectively.

The efficiency of pure blue organic light-emitting diodes (OLEDs) still needs to be improved, which is limited by the utilization of the forbidden transition triplet excitons and low light-out-coupling efficiency in devices. Herein, two blue emitters were developed through combining multiple diphenylamine (DPA) donors with an oxygen-bridged boron (DBA) or triphenyl triazine (TRZ) acceptor. Notably, a narrow-band deep blue emission with a peak of 423 nm and a full-width at half-maximum (FWHM) of 34 nm is realized for the boron-based emitter in toluene solution. Thanks to their multiple charge transfer (CT) channels and high orientated disk-like structure, high radiative transition rates ( k r > 108 s−1) and high horizontal emitting dipole ratios (Θ > 80%) can be realized simultaneously. Meanwhile, the introduction of the peripheral DPA units can also provide multiple localized triplet (3LE) states for spin up-conversion of forbidden transition triplet excitons. Owing to the effective up-conversion of triplet excitons and high light-out-coupling efficiency, maximum external quantum efficiency of more than 10% is achieved for the boron emitter-based pure blue OLEDs with a Commission Internationale de l’Eclairage (CIE) coordinates of (0.14, 0.08).

Enhancing the rate of reverse intersystem crossing (krisc) and the rate of radiative transition (kr) has been regarded as the key to improve molecular design strategy in the field of thermally activated delayed fluorescence (TADF) materials. Herein, two sky-blue donor–acceptor (D–A)-type TADF materials, namely, CzDCNPy and tBuCzDCNPy, were designed following a strategy of controlling the energy difference among the charge-transfer singlet state (1CT), local exciton triplet state (3LE), and charge-transfer triplet state (3CT). Significantly different from most previously reported TADF materials, large values of kr and krisc and a nearly 100% exciton utilization efficiency were simultaneously achieved despite nonobvious delayed fluorescence and a large value of the singlet–triplet energy difference (ΔEST) being observed. This work presents a view that photoinduced delayed fluorescence and a small ΔEST are sufficient but not necessary for TADF materials. It also provides a reference that the high-energy 3LE ...

A novel iridium complex grafting hole-transporting triphenylamine (TPA) unit onto cyclometalated ligand, namely t-BuPyrPyTPA) 2 Ir(acac), was successfully synthesized and characterized. The photophysical, electrochemical and DFT/TD-DFT calculation, as well as electroluminescence properties of this iridium complex were fully investigated. Meanwhile, the PLEDs employing (t-BuPyrPyTPA) 2 Ir(acac) as dopant presented stable NIR emission peaked at 697 nm and a shoulder at 764 nm with a highest external quantum efficiency ( EQE ) of 0.56% at 4 wt% dopant concentration. These results demonstrate that expanding the conjugation length of the ligand is an effective way to achieve NIR emission.

An organic compound exhibiting simultaneously reversible switch between its emission colors and luminescence mechanisms, possessing high contrast from deep blue normal fluorescence (NF) to yellow thermally activated delayed fluorescence (TADF), is reported. Based on these two complementary colors, white-light emission combining NF and TADF from a single compound can be achieved in various states. Experimental results and density functional theory calculations indicate that the controllable conformational distribution under thermal and mechanical activation is the mechanism responsible for the reversible switching behavior.

The design of orange-light emitting, thermally activated, delayed fluorescence (TADF) materials is necessary and important for the development and application of organic light-emitting diodes (OLEDs). Herein, two donor–acceptor–donor (D–A–D)-type orange TADF materials based on fluorenone and acridine, namely 2,7-bis(9,9-dimethylacridin-10(9H)-yl)-9H-fluoren-9-one (27DACRFT, 1) and 3,6-bis(9,9-dimethylacridin-10(9H)-yl)-9H-fluoren-9-one (36DACRFT, 2), were successfully synthetized and characterized. The studies on their structure–property relationship show that the different configurations have a serious effect on the photoluminescence and electroluminescence performance according to the change in singlet–triplet splitting energy (ΔEST) and excited state geometry. This indicates that a better configuration design can reduce internal conversion and improve triplet exciton utilization of TADF materials. Importantly, OLEDs based on 2 exhibited a maximum external quantum efficiency of 8.9%, which is higher than the theoretical efficiency of the OLEDs based on conventional fluorescent materials.

A series of new small molecules based on symmetric electron-acceptor of 1,3,4-oxadiazole moiety or its asymmetric isomer of 1,2,4-oxadiazole unit were successfully synthesized and applied to solution-processable blue phosphorescent organic light-emitting diodes for the first time, and their thermal, photophysical, electrochemical properties and density functional theory calculations were studied thoroughly. Due to the high triplet energy levels (ET, 2.82–2.85 eV), the energy from phosphorescent emitter of iridium(III) bis[(4,6-difluorophenyl)-pyridinate-N,C2′]picolinate (FIrpic) transfer to the host molecules could be effectively suppressed and thus assuring the emission of devices was all from FIrpic. In comparison with the para-mode conjugation in substitution of five-membered 1,3,4-oxadiazole in 134OXD, the meta-linkages of 1,2,4-isomer appending with two phenyl rings cause the worse conjugation degree and the electron delocalization as well as the lower electron-withdrawing ability for the other 1,2,4-oxadiazole-based materials. Noting that the solution-processed device based on 134OXD containing 1,3,4-oxadiazole units without extra vacuum thermal-deposited hole/exciton-blocking layer and electron-transporting layer showed the highest maximum current efficiency (CEmax) of 8.75 cd/A due to the excellent charge transporting ability of 134OXD, which far surpassed the similar devices based on other host materials containing 1,2,4-oxadiazole units. Moreover, the device based on 134OXD presented small efficiency roll-off with current efficiency (CE) of 6.26 cd/A at high brightness up to 100 cd/m2. This work demonstrates different nitrogen and oxygen atom orientations of the oxadiazole-based host materials produce major impact on the optoelectronic characteristics of the solution-processable devices.

Herein, a new near-infrared (NIR) material, 4-(9-(4-(diphenylamino)phenyl)naphtho[2,3-c][1,2,5]thiadiazol-4-yl)benzonitrile (TPA-NZC), was designed and synthesized with the incorporation of an ancillary acceptor (cyanophenyl) into the donor-acceptor (D-A) molecular backbone of a red emitter TPA-NZP (4,9-diphenylnaphtho[2,3-c][1,2,5]thiadiazole). Compared with TPA-NZP, TPA-NZC exhibits an NIR emission (λmax = 710 nm) with a large redshift, as well as a maintained photoluminescence efficiency (ηPL) of 17% in film. Moreover, the non-doped OLED based on TPA-NZC emitter exhibits an excellent NIR emission at 702 nm with a maximum EQE of 1.2%, while the doped device achieves a deep-red emission at 656 nm with a maximum EQE of 3.2%. This work further verifies the reliability of “hot exciton” and hybridized local and charge-transfer state (HLCT) mechanism, as well as provides a strategy to design a narrow bandgap light-emitting material by introducing cyanophenyl as an ancillary acceptor in D-A systems.

Two novel D–σ–A host materials 11,11-bis(9-phenyl-9H-carbazol-3-yl)-11H-benzo[4,5]imidazo[1,2-a]indole (BII–BCz) and 4,4′-(11H-benzo[4,5]imidazo[1,2-a]indole-11,11-diyl)bis(N,N-diphenylaniline) (BII–TPA) are synthesized by using the sp3 carbon attached to a newly designed 11H-benzo[4,5]imidazo[1,2-a]indole building block to link two electron-donating groups. The resulting materials feature high triplet energy levels, good thermal properties and suitable photophysical properties as universal hosts for full-color phosphorescent organic light-emitting diodes (OLEDs). Both BII–BCz and BII–TPA reveal excellent performances in blue, green, yellow, orange and red phosphorescent OLEDs with the same device structure. The employment of the new D–σ–A materials as single hosts in white OLEDs with a simple device structure allows us to achieve state-of-the-art performances. A single-emissive-layer white device based on BII–BCz demonstrates the highest performance with an external quantum efficiency up to 28.2% at 1000 cd m−2. Furthermore, this device displays extremely stable emission spectra, with a ΔCIE of only (0.009, 0.005) from 1000 to 10 000 cd m−2.

With the advantages of facile one-pot synthesis and THF-irrigating purification, we first developed novel cyclic compounds with deep blue thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) dual emission even in the as-spun films. Careful crystal analysis, combined with theoretical calculations, reveal that abundant inter- and intra-molecular interactions, whatsoever the molecular packing, are obligated to unique RTP properties. These results open up a new study of compounds with multiple acceptors and donors, and represent an important step in the further development of deep blue TADF and easy RTP emission.

The strong electronegativity of sp-hybridized carbons, contributed by their large s character (50%), inspired the development of diphenylethyne as an electron acceptor to construct a sky-blue thermally activated delayed fluorescence material, 1,2-bis(4-(10H-phenoxazin-10-yl)phenyl)ethyne (DPE-DPXZ), using 10H-phenoxazine (PXZ) as an electron donor fragment. A sky-blue organic light-emitting diode employing DPE-DPXZ as the emitter demonstrated an external quantum efficiency exceeding 10%. Furthermore, another alkyne derivative, 1,2-bis(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)ethyne (DPE-DDMAc), in combination with 9,9-dimethyl-9,10-dihydroacridine (DMAc) as the donor was also studied to explore the singlet–triplet splitting energy governed by donor–acceptor alternation.

We developed a novel highly efficient blue-light-emitting polymer (P0) containing the alternating electron-deficient diphenylsulfone and the electron-rich 4-octyloxy-aniline moieties, which was synthesized by a palladium catalyzed C–N coupling reaction. Photophysical and light-emitting device characterization confirmed the delayed fluorescence mechanism of this copolymer. A polymer light-emitting diode based on P0 exhibited pure blue emission with CIE coordinates of (0.16, 0.10), which has a maximum external quantum efficiency of 5.3%. In addition, a series of color-tunable polymers that exhibit delayed fluorescence with light emission ranging from sky blue to bluish green and improved efficiency were developed by incorporating a ditriphenylamine-functionalized triazine unit. Our strategy represents a novel approach for the construction of polymers with delayed fluorescence and high efficiency.

Two new zig-zag type di- and mono-nuclear platinum(II) complexes of (BuPh-BDIQ)Pt2(dpm)2 and (BuPh-BDIQ)Ptdpm were synthesized and characterized by using a zig-zag type cyclometalating ligand 3,10-di(tert-butyl)-5,12-bis(4-(tert-butyl)phenyl)-benzodiisoquinoline (BuPh-BDIQ). Their single-crystal structures, and photophysical, electrochemical and electroluminescent properties were primarily investigated. Compared with (BuPh-BDIQ)Ptdpm, (BuPh-BDIQ)Pt2(dpm)2 exhibited a significantly increased photoluminescent efficiency of 3.64% and a red-shifted near-infrared (NIR) emission peak at 718 nm owing to its enhanced rigid planar structure in a nitrogen atmosphere. As a result, only (BuPh-BDIQ)Pt2(dpm)2 presented NIR electroluminescent emission in a doped polymeric light-emitting diode. The highest external quantum efficiency of 0.97% and a radiant intensity of 146 μW cm−2 were observed for the device at 2 wt% dopant concentration, which is higher than the values of previous NIR-emitting di-nuclear platinum complexes constructed with cyclometalated ligands. Furthermore, efficiency roll-off was efficiently inhibited. This indicates that high-efficiency NIR-emitting di-nuclear platinum complexes can be obtained by designing a zig-zag type C^N–C^N tetradentate cyclometalating ligand with a big rigid planar saw band.

Electroluminescence originating from layer-to-layer charge transfer (LLCT) in organic light-emitting diodes (OLEDs) was early observed, whereas, the inferior performances limit their practical applications. In this work, we demonstrated an efficient approach to improve the overall performances of LLCT-based planar heterojunction OLEDs by simply diluting an n-type electron transport material into a carbazole-based matrix material to suppress excited-state quenching. As a result, an optimized device with a peak current efficiency of 41 cd A−1 (corresponding to a maximum external quantum efficiency of 12.6%) exhibited significantly enhanced efficiencies and much higher brightness at high current densities in contrast to the control devices without a mixture layer. We illustrated that even with a similar narrow recombination region, it is feasible to achieve excellent fluorescent OLEDs with light emission originating from LLCT. We believe that this work should pave the way for developing high-performance LLCT-based OLEDs with a high efficiency, reduced efficiency roll-off and sufficiently large maximum brightness.

Marching toward highly efficient long-wavelength organic light-emitting diodes (OLEDs) is paramount but formidable challenge, and rational manipulation of molecular configuration and excited state dynamic processes are of great importance to harvest dark triplet exciton and suppress non-radiative transition for excellent light emission properties. Herein, we introduced a novel electron acceptor 11H-indeno [1,2-b] quinoxalin-11-one (IQ) as a building-block to construct two bright red light-emitting regioisomers of IQ-oTPA and IQ-pTPA, which exhibit entirely different exciton dynamic processes of thermally activated delayed fluorescence (TADF) and conventional fluorescence (CF) respectively. According to theoretical calculation and photophysical characterization, the energy gap, energy level alignment and spin–orbit coupling (SOC) effects of charge-transfer singlet state (1CT), local excited triplet state (3LE) and charge-transfer triplet state (3CT) together with the molecular geometry rigidity play a critical role in the triplet exciton up-conversion processes. Maximum external quantum efficiencies of 20.6% and 3.5% with emission peaks of 604 and 642 nm were achieved for the proof-of-concept electroluminescent devices based on IQ-oTPA and IQ-pTPA respectively, which are among the state-of-the-art performance for red-emission TADF and CF OLEDs and provide new insights for the molecular design tactic of high-performance red OLEDs.

Efficient and robust organic light-emitting diodes (OLEDs) have always been of great interest for both academia and industry. In this work, two electroluminescence donor-π-acceptor structure materials 3,6-TC and 3,6-T2C were synthesized and investigated on their excited state properties and electroluminescence performances. The non-doped and doped OLED of the two materials both exhibited high maximum external quantum efficiency (EQE) of near 5% and exciton utilizing efficiency (EUE) of over 60%. More importantly, the introduction of an extra cyano group of 3,6-T2C facilitated a fine modulation of hybridized local and charge-transfer (HLCT) excited state with a crossed dipole of CT transition and an energy favorable high-lying reverse intersystem crossing (RISC), which contributed to a more stable photoluminescence (PL) and EUE than the 3,6-TC. This work provided a novel design strategy to realize high-performance OLED device by the fine modulation in HLCT state.

Efficient thermally activated delayed fluorescence (TADF) relies on fast reverse intersystem crossing (RISC) that promotes triplet-singlet spin conversion to shorter excited state lifetime, which is a decisive factor to achieve high electroluminescence performance. In this study, two new TADF emitters BenCN-PXZ and BDCN-PXZ employing an asymmetric donor-acceptor framework are designed and synthesized by combining different CN-modified acceptor units with phenoxazine (PXZ) as a strong electron donor unit. The influence of CN-group with different substituting sites is systematically compared to highlight the structure-property relationship. BenCN-PXZ and BDCN-PXZ exhibit red emission with emission peak over 600 nm and short delayed lifetime within 0.6 µs in the neat film. Surprisingly, the delayed lifetime of BDCN-PXZ is still shorter than 1 µs even being doped into CBP host, implying their promising application in organic light-emitting devices (OLEDs). Both Non-doped and doped OLEDs are fabricated for comparison, among which, doped device based on BDCN-PXZ: CBP presented superior device performances and negligible efficiency roll-off (2.8%) at 1000 cd m−2, which is almost the best results for orange-red TADF-based OLEDs.