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Developing high-performance host materials is one of the biggest challenges for blue and white thermally activated delayed-fluorescence (TADF) organic light-emitting diode (OLED) technology due to the rigorous requirements of both efficient carrier flux ability and high triplet energy (

Developing full-color organic ultralong room temperature phosphorescence (OURTP) materials with continuously variable afterglow emission is of considerable practical importance in diverse optoelectronic applications but remains a formidable challenge. Here, we present an effective strategy for on-demand engineering of afterglow color in water-soluble polymeric systems via efficient phosphorescence Förster resonance energy transfer. Using a blue afterglow emitting water-soluble polymer as host and a series of fluorescent emitters with varied emissive colors as guests, afterglow emission is rationally modulated, conferring the full-color afterglow emission ranging from blue to red and even white with ultralong lifetimes up to 4.2 s and photoluminescence quantum yields of 36%.These water-soluble multicolor-emitting polymeric afterglow systems can function as OURTP security inks, and multilevel information encryption was successfully established by RGB-based multicolor security printing. These results present important guidance in developing high-performance afterglow polymers with on-demand color tuning ability for remarkable optoelectronic applications.

Organic ultralong room temperature phosphorescence (OURTP) materials having stimuli-responsive attributes have attracted great attention due to their great potential in a wide variety of advanced applications. It is of fundamental importance but challengeable to develop stimuli-responsive OURTP materials, especially such materials with modulated optoelectronic properties in a controlled manner probably due to the lack of an authentic construction approach. Here, we propose an effective strategy for OURTP materials with controllably regulated stimuli-responsive properties by engineering the resonance linkage between flexible chain and phosphor units. A quantitative parameter to demonstrate the stimuli-responsive capacity is also established by the responsivity rate constant. The designed OURTP materials demonstrate efficient photoactivated OURTP with lifetimes up to 724 ms and tunable responsivity rate constants ranging from 0.132 to 0.308 min

We report the synthesis of 5,7,12,14-tetraphenyl-substituted 6,13-dihydro-6,13-diazapentacene and its fully aromatic 6,13-diazapentacene congener. Both arylated diazapentacenes were characterized by X-ray crystallography to investigate their solid-state structures and by UV–vis spectroscopy and cyclic voltammetry to unveil their electronic properties. The experimental results are complemented with theoretical investigations. The semiconductor properties of both diazapentacene derivatives were assessed in organic field-effect transistors, whereby the fully aromatized compound showed comparably less abundant n-type behavior.

A series of quinoidal N,N′‐diaryldiaza‐N,N′‐dihydropentacenes (Quino) was prepared in a two‐step reaction, starting from quinacridone. Oxidation of Quino furnishes stable radical cations, isoelectronic to the radical anions of the azaacenes, whereas the dicationic species are isoelectronic to neutral azapentacenes. The spectroscopic properties of the diaryldiazapentacenes and their oxidized mono‐ and dications are equivalent to that of the dianion of tetraazapentacene (TAP), its radical anion and the neutral TAP., Radicalized: A series of quinoidal N,N′‐5,7,12,14‐tetraaryl‐5,12‐dihydropentacenes were oxidized into their radical cations and dications, the latter electronically resembling highly acceptor‐substituted diazapentacenes.

Achieving afterglow organic light-emitting diodes (OLEDs) that exhibit the organic ultralong room temperature phosphorescence (OURTP) emission after switching off the applied voltage is highly attractive. However, it is difficult to obtain appropriate emitting layers that are of excellent charge transport ability and OURTP properties simultaneously to fabricate highly efficient afterglow OLEDs. Here, we report an easy but effective strategy to construct afterglow OLEDs via host–guest doping by adopting the excellent carrier transporting materials as rigid host and the commendable OURTP emitters as guest. The resultant green afterglow OLEDs exhibit the state-of-the-art maximum external quantum efficiency, luminance, and OURTP lifetimes of up to 1.47%, 743 cd m−2, and 356 ms, respectively, with the low turn-voltage of 4.4 V. Due to the inherent stable afterglow properties and outstanding carrier transport ability of the emitting layer, the OLEDs show admirable afterglow emission stability with the intensity and lifetimes keeping almost the same for more than ten repeated voltage pulses. The current work paves the way to develop highly efficient and stable afterglow OLEDs by host–guest doping.

Three phosphine sulfide-based bipolar host materials, viz&nbsp, CzPhPS, DCzPhPS, and TCzPhPS, were facilely prepared through a one-pot synthesis in excellent yields. The developed hosts exhibit superior thermal stabilities with the decomposition temperatures (Td) all exceeding 350 °C and the melting temperatures (Tm) over 200 °C. In addition, their triplet energy (ET) levels are estimated to be higher than 3.0 eV, illustrating that they are applicable to serve as hosts for blue phosphorescent organic light-emitting diodes (PhOLEDs). The maxima luminance, current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of 17223 cd m−2, 36.7 cd A−1, 37.5 lm W−1, and 17.5% are achieved for the blue PhOLEDs hosted by CzPhPS. The PhOLEDs based on DCzPhPS and TCzPhPS show inferior device performance than that of CzPhPS, which might be ascribed to the deteriorated charge transporting balance as the increased number of the constructed carbazole units in DCzPhPS and TCzPhPS molecules would enhance the hole-transporting ability of the devices to a large extent. Our study demonstrates that the bipolar hosts derived from phosphine sulfide have enormous potential applications in blue PhOLEDs, and the quantity of donors should be well controlled to exploit highly efficient phosphine sulfide-based hosts.

Three stable N,N’‐diarylated dihydroazaacene radical cations were prepared by oxidation of neutral N,N’‐diarylated dihydroazaacenes synthesized via palladium‐catalyzed Buchwald‐Hartwig aminations of aryl iodides with N,N’‐dihydroazaacenes. Both neutral as well as oxidized species were investigated via UV‐vis spectroscopy, single crystal analysis, and DFT calculations. All the radical cations are surprisingly stable—their absorption spectra in dichloromethane remain unchanged in ambient conditions for at least 24 hours., Oxidation of N,N’ ‐diarylated dihydroazaacenes furnishes three stable dihydroazaacene radical cations characterized by means of UV‐vis spectroscopy, single crystal analysis, and DFT calculations.

The synthesis, property evaluation, and single crystal X‐ray structures of four 5,7,12,14‐tetrafunctionalized diazapentacenes are presented. The synthesis of these compounds either starts from tetrabromo‐N,N‐dihydrodiazapentacene or from a diazapentacene tetraketone. Pd‐catalyzed coupling or addition of a lithium acetylide gave the precursors that furnish, after further redox reactions, the diazapentacenes as stable crystalline materials. The performance of the tetraphenyl‐substituted compound as n‐channel semiconductor was evaluated in organic field effect transistors., Four in one strike: The simple construction of fourfold substituted 6,13‐diazapentacenes by using Suzuki cross‐coupling or nucleophilic addition to a double quinone is described (see scheme).

The synthesis, properties and solid state X-ray single crystal structures of two new rubrene-derivatives, viz diazarubrene (4,4'-(6,12-diphenyltetracene-5,11-diyl)dipyridine) and tetraazarubrene (5,6,11,12-tetra(pyridin-4-yl)tetracene), are reported. Both the azarubrenes are more oxidatively stable than rubrene itself and show very similar optical properties but differ in their crystal packing from that of rubrene.

The exploration of host materials with simultaneously excellent electrical properties and high triplet energy levels is highly essential but challenging in the fields of blue and white phosphorescence (Ph) and thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Herein, the symmetric V-shaped triazine host of DCzT in D-A-D molecular configuration featuring non-covalent intramolecular interactions (NCIs) was designed and synthesized through the replacement of phenyl core of highly twisted blue host of mCP by the acceptor unit of 2,4-dichloro-1,3,5-triazine. By means of the NCIs, DCzT demonstrates a relatively closed plane, thus boosting ordered molecular packing arrangement for the formation of carrier transport channel to acquire enhanced and balanced electrical performance at a high triplet energy level. Excitingly, highly efficient white TADF OLEDs was achieved displaying maximum luminance of 12000 cd m−2 and external quantum, current and power efficiencies of 23.2%, 66.9 cd A-1 and 70.0 lm W−1, respectively. This work highlights that the NCI affords a simple and intelligent way to regulate the electrical attributes of organic optoelectronic materials.

A series of novel molecules with wide bandgap based on electron-withdrawing diphenyl phosphine oxide units and electron-donating carbazolyl moieties through insulated unique linkages of flexible chains terminated by oxygen or sulfur atoms as solution-processable host materials were successfully synthesized for the first time, and their thermal, photophysical, and electrochemical properties were studied thoroughly. These materials possess high triplet energy levels ( E T , 2.76–2.77 eV) due to the introduction of alkyl chain to interrupt the conjugation between electron-donor and electron-acceptor. Such high E T could effectively curb the energy from phosphorescent emitter transfer to the host molecules and thus assuring the emission of devices was all from the blue phosphorescent emitter iridium (III) bis [(4,6-difluorophenyl)-pyridinate- N ,C2′]picolinate (FIrpic). Among them, the solution-processed device based on CBCR6OPO without extra vacuum thermal-deposited hole-blocking layer and electron-transporting layer showed the highest maximum current efficiency (CE max ) of 4.16 cd/A. Moreover, the device presented small efficiency roll-off with current efficiency (CE) of 4.05 cd/A at high brightness up to 100 cd/m 2 . Our work suggests the potential applications of the solution-processable materials with wide bandgap in full-color flat-panel displays and organic lighting.

Two thioxanthone-derived isomeric series of thermally activated delayed fluorescence (TADF) emitters 1,6-2TPA-TX/3,6-2TPA-TX and 1,6-2TPA-TXO/3,6-2TPA-TXO are developed for organic light-emitting diodes (OLEDs). Blue emission devices based on symmetrical 3,6-2TPA-TX with common vertical transition route realize an extremely high external quantum efficiency (EQE) of 23.7%, and an ever highest EQE of 24.3% is achieved for yellow emission devices based on 3,6-2TPA-TXO by solely changing the sulfur atom valence state of the thioxanthone core. In contrast, their corresponding asymmetric isomers are affected by intramolecular energy transfer and more severely by a nonradiative deactivation pathway, to give much low EQE values (

A chromaticity-adjustable yellow thermally activated delayed fluorescence (TADF) material, PXZDSO2 as a triplet harvester provides a rational device concept, giving two-color and three-color pure organic white organic light-emitting diodes (WOLEDs) with unprecedented color-rendering index of 95 and external quantum efficiency of 19.2%.

Thioxanthone derivatives consisting of undecorated carbazole as an electron donor and thioxanthone (TXO) or 9H-thioxanthen-9-one-S,S-dioxide (SOXO) as an electron acceptor in a donor-acceptor (D-A) or donor-acceptor-donor (D-A-D) structure were developed as thermally activated delayed fluorescence emitters to fabricate highly efficient fluorescent organic light emitting diodes. Their emission color was successfully tuned from blue to yellow by changing the sulfur atom valence state of the thioxanthone unit to tune intramolecular charge transfer effect. Their thermal, electrochemical, photophysical, and electroluminescent properties, and theoretical calculations were systematically investigated to illustrate the molecular structure and property relationships. Maximum external quantum efficiency (EQE) of 13.6% with Commission Internationale de L'Eclairage coordinates of (0.37, 0.57) was achieved for green light emission CzSOXO consisting of SOXO and carbazole in a D-A structure. Blue light emission CzTXO and DCzTXO consisting of TXO and carbazole in a D-A and D-A-D structure could also give EQE values exceeding 11%. Their efficiency roll-off with increasing current density was simulated by adopting triplet-triplet annihilation model, indicating that the TXO derivatives suffer more severe efficiency roll-off because of their relatively long delayed fluorescence lifetime (τ(D)).

Issues concerning excited state lifetime (τTADF) tuning of thermally activated delayed fluorescence (TADF) materials are critical for organic light emitting diode (OLED) applications and other specific fields. For TADF-OLEDs, employing emitters with a short τTADF gives rise to suppressed singlet–triplet annihilation (STA) and triplet–triplet annihilation (TTA), leading to reduced efficiency roll-off at practical relevant brightness (100 and 1000 cd m−2 for display and illumination applications, respectively). Through molecular design, exciton dynamic process rate constants including fluorescence (kF), intersystem crossing (kISC), internal conversion (kIC) and reverse intersystem crossing (kRISC) are selectively altered, affording four representative TADF emitters. Based on lifetime and quantum yield measurements, kF, kISC, kIC and kRISC are calculated for four emitters and their interrelationship matches corrected time-dependent density functional theory simulation. Among them, even with a small kF, low photoluminescence quantum efficiency (Φ) and large kISC, molecules with a small singlet–triplet splitting energy (ΔEST) and lowest charge transfer triplet excited state (3CT) eventuate in shortening the τTADF. Herein, kRISC, which is inversely proportional to ΔEST, turns out to be the rate-limited factor in tuning the τTADF (“rate limited effect” of the RISC process). As revealed by flexible potential surface scanning, PyCN–ACR exhibited a moderate kF, reduced kIC and enlarged kRISC, resulting in a short τTADF and a moderate Φ with orange-red emission. OLEDs containing PyCN–ACR as the emitting guest achieved orange-red TADF-OLEDs with an emission peak at 590 nm and the best external quantum efficiencies (EQEs) of 12.4%/9.9%/5.1% at practical luminances of 100/1000/10 000 cd m−2.

Fluorescent organic light-emitting diodes capable of radiative utilization of both singlet and triplet excitons are achieved via a simple double-layer planar pn hetero-junction configuration without a conventional emission layer, leading to high external quantum efficiency above 10% and extremely low driving voltages close to the theoretical minima.

Two novel evaporation- and solution-process-feasible thermally activated delayed fluorescence emitters, green-light-emission ACRDSO2 and yellow-light-emission PXZDSO2, based on a brand-new electron-acceptor moiety thianthrene-9,9',10,10'-tetraoxide, are developed for organic light-emitting diodes. The solution-processed devices, without any hole-transport layer, exhibit competitive performance and reduced efficiency roll-off compared with corresponding vacuum-deposited devices.

Two novel naphtho[1,2-d]imidazole derivatives are developed as deep-blue, light-emitting materials for organic light-emitting diodes (OLEDs). The 1H-naphtho[1,2-d]imidazole based compounds exhibit a significantly superior performance than the 3H-naphtho[1,2-d]imidazole analogues in the single-layer devices. This is because they have a much higher capacity for direct electron-injection from the cathode compared to their isomeric counterparts resulting in a ground-breaking EQE (external quantum efficiency) of 4.37% and a low turn-on voltage of 2.7 V, and this is hitherto the best performance for a non-doped single-layer fluorescent OLED. Multi-layer devices consisting of both hole- and electron-transporting layers, result in identically excellent performances with EQE values of 4.12–6.08% and deep-blue light emission (Commission Internationale de l'Eclairage (CIE) y values of 0.077–0.115) is obtained for both isomers due to the improved carrier injection and confinement within the emissive layer. In addition, they showed a significantly better blue-color purity than analogous molecules based on benzimidazole or phenanthro[9,10-d]imidazole segments.

A series of blue-light-emitting conjugated polymers based on electron-donating trifluoren-2-ylamine and electron-deficient dibenzothiophene-S,S-dioxide were synthesized via typical Suzuki coupling reactions. Their thermal, photophysical and electrochemical properties were fully studied. Owing to the excellent thermal stability, film-forming ability as well as the favorable energy levels of the polymers, highly efficient non-doped single-layer blue devices by using these polymers as an emitting layer (EML) were achieved. Among them, the device based on PSFOFN1 showed the highest maximum current efficiency (CEmax) of 1.99 cd/A. Moreover, the device presented small efficiency roll-off with current efficiency (CE) of 1.97 cd/A at high brightness up to 100 cd/m2. In addition, the Commission Internationale de L’Eclairage (CIE) coordinates of all the devices are very close to the deep blue region. Our findings suggest the potential applications of the polymers in full-color flat-panel displays and organic lighting.

A series of blue emitters incorporating spiro[fluorene-9,9′-thioxanthene] or spiro[fluorene-9,9′-thioxanthene-S,S-dioxide] as the core and phenylcarbazole or triphenylamine as the arms were designed and synthesized. Their spiro conformation is beneficial for their thermal stability and for reducing the trend of aggregation quenching. By tuning the valence of the sulfur atom, highly efficient local excited (LE) state deep blue emitters and charge-transfer (CT) state blue emitters are obtained. The devices based on the LE emitters TPA-S and CzB-S as the nondoped emissive layer exhibit high external quantum efficiency of 1.76% and 2.03% and Commission Internationale de l’Eclairage (CIE) coordinates of (0.158, 0.039) and (0.160, 0.054), respectively, and their CIEy values are among the smallest ever reported for the deep blue OLEDs and are readily very close to that of the inorganic light-emitting diode [CIE (0.16, 0.02)]. The nondoped device based on the CT emitter TPA-SO2 as the emissive layer also exhibits...

Two novel bipolar isomeric blue fluorophores, PPI-TPA-SO2-1 and PPI-TPA-SO2-2, consisting of electron-withdrawing phenanthro[9,10-d]imidazole and sulfone-locked electron-donating triphenylamine, were designed and synthesized. The sulfone lock induces a more twisted molecular conformation, and thus a higher triplet energy level and better triplet exciton confining ability compared with the analogue TPA-PPI without the sulfone lock. In addition, the introduced sulfone lock also offers the developed materials improved electron affinities and an electron dominant transporting ability. They were utilized as the blue emitter and the host for a yellow phosphorescent emitter to fabricate fluorescence–phosphorescence (F–P) hybrid white organic light-emitting diodes (WOLEDs) in a single-emissive-layer architecture, giving forward-viewing maximum current efficiencies of 44.2 and 47.6 cd A−1, power efficiencies of 49.5 and 53.4 lm W−1, and external quantum efficiencies of 14.4% and 15.6%, respectively, which are much higher than those of the devices based on TPA-PPI (29.5 cd A−1, 33.1 lm W−1, and 9.6%) due to their superior singlet and triplet exciton separation and utilization ability over TPA-PPI. These efficiencies are also the highest values ever reported for the F–P hybrid WOLEDs in a similar architecture, and their power efficiencies are even comparable with most reported highly efficient all phosphorescent WOLEDs without using any out-coupling technology.

A series of polarity-tunable host materials were developed based on oligocarbazoles and diphenylphosphine oxide, and their polarities can be tuned through increasing distance of acceptor and donor units. Density functional theory calculations were employed, and photoluminescence spectra in different polar solvents were measured to illustrate different polarities of these host materials. As CZPO has relatively stronger polarity, electroluminescence (EL) spectrum of solution-processed device based on 6 wt % PXZDSO2:CZPO is 7 nm red-shifted relative to that of other host materials based devices. Besides, a comparable impressive external quantum efficiency (EQE) value of 18.7% is achieved for an evaporation-processed yellow device consisting of FCZBn, which is superior to that of the device based on CBP (4,4′-dicarbazolyl-1,1′-biphenyl) (17.0%), and its efficiency roll-off is also obviously reduced, giving an EQE value as high as 16.3% at the luminance of 1000 cd/m2. In addition, from CZPO to FCZBn as the pol...

Organic light-emitting diodes (OLEDs) combining low driving voltage and high efficiency are designed by employing conventional and thermally activated delayed fluorescence emitters through modulation of excitons generated at the planar p-n heterojunction region. To date, this approach enables the highest power efficiency for yellow-green emitting fluorescent OLEDs with a simplified structure.