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Multiresonant thermally activated delayed fluorescence (MR-TADF) compounds are attractive for use in organic light-emitting diodes as they show narrowband emission, are bright, and can harvest both singlet and triplet excitons for the emission of light. Reflected in the paucity of examples of orange-to-red emitters, developing MR-TADF emitters that emit beyond the green remains an outstanding materials design challenge. In this work, we report one of the first carbonyl-based orange MR-TADF emitters, DDiKTa-A, which is based on the dimerization of the sky-blue emitting DiKTa through a central aniline bridge. DDiKTa-A emits at λPL of 562 nm and has high photoluminescence quantum yield of 92% in 2 wt% doped films in mCP. DDiKTa-A exhibits temperature dependent steady-state photoluminescence in 2-MeTHF, acting as an indirect indicator of the polarity of the medium. The OLEDs with DDiKTa-A showed an EQEmax of 20.3%, but with significant efficiency roll-off (EQE100 of 13.2%). The EQEmax was improved, and the efficiency roll-off mitigated by incorporating an assistant dopant, 4CzIPN, within the emissive layer of the device. The hyperfluorescence device showed an EQEmax of 24.3%, which decreased to 22.5 and 14.6% at 100 and 1000 cd m−2, respectively. [ABSTRACT FROM AUTHOR]

Herein, we report a fluorene-bridged double carbonyl/amine-based MR TADF emitter DDiKTa-F, formed by locking the conformation of the previously reported compound DDiKTa. Using this strategy, DDiKTa-F exhibited narrower, brighter, and red-shifted emission. The OLEDs with DDiKTa-F emitted at 493 nm and showed an EQEmax of 15.3% with an efficiency roll-off of 35% at 100 cd m−2. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) and hot excitons are two distinct exciton harvesting mechanisms that can lead to 100% internal quantum efficiency in organic light-emitting diodes (OLEDs). Herein, we show that with judicious molecular engineering, the resulting structurally similar compounds emit via distinct photophysical mechanisms, which has a direct consequence on the OLED efficiency. When the pyrazine core is substituted with four carbazoles, the molecule 4CzPyz shows TADF in doped PPT film, with ΦPL of 75%, ΔEST of 0.23 eV and τd of 150 μs. The device based on 4CzPyz emits in the sky-blue (λEL = 486 nm) with an EQEmax of 24.1%. When one carbazole is replaced by an ortho-biphenyl, the ΔEST of 3CzBPz increases to 0.29 eV, the ΦPL decreases to 56%, and the TADF character is largely suppressed in the PPT film. However, a RISC process between higher-lying triplet excited states and the S1 state is hypothesized to be operational, supported by a combined photophysical and DFT study, to rationalize how the device with 3CzBPz shows an EQEmax of 9.6% (λEL = 464 nm), reflecting that greater than 86% of the excitons are converted into light in the OLED. When two ortho-biphenyl groups are connected to the pyrazine core, the ΔEST of 2CzBPz is further increased to 0.34 eV while the ΦPL is reduced to 45% in the PPT film. The DFT and photophysical studies indicate that 2CzBPz should act as a traditional blue fluorescence emitter. The OLED devices with 2CzBPz bear this out and exhibit an EQEmax 3.2% at a λEL of 446 nm. These results show how subtle structural changes modulate the efficiency of the triplet exciton harvesting mechanisms and provide new design directions for highly efficient blue emitters for OLEDs. [ABSTRACT FROM AUTHOR]

Nitrogen-containing polycyclic aromatic hydrocarbons (N-PAH) have been widely used as deep lowest unoccupied molecular orbital (LUMO) acceptors in donor–acceptor (D–A) red thermally activated delayed fluorescence (TADF) emitters and in organic light-emitting diodes (OLEDs). However, most of the studies have focused disparately on donor/acceptor combinations to yield efficient emitters, while a methodological study investigating the influence of nitrogen (N) doping ratios on the ground and excited states of PAH acceptors is rare. Here, we report a family of four different N-PAH acceptors containing different numbers of nitrogen atoms within the N-PAH and their use in D–A TADF emitters, DMACBP, DMACPyBP, DMACBPN and DMACPyBPN, when coupled to the same donor, 9,9-dimethyl-9,10-dihydroacridine (DMAC). As the nitrogen content in the acceptor increases the LUMO becomes progressively more stabilized while the singlet–triplet energy gap (ΔEST) decreases and the rate constant for reverse intersystem crossing (kRISC) increases. In particular, introducing nitrogen at the 10-position of dibenzo[a,c]phenazine (BP) leads to a more than ten-fold enhancement in kRISC in DMACPyBP and DMACPyBPN compared to DMACBP and DMACBPN. Among the OLEDs with all four emitters that with DMACBPN demonstrates the highest EQEmax of 19.4% at an emission peak of 588 nm, while the deepest red emitting device employed DMACPyBPN (λEL = 640 nm) with an EQEmax of 5.4%. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials have received enormous attention and the mechanism behind them has been investigated in depth. It has been found that some donor–acceptor (D–A) type TADF emitters could obviously exhibit dual stable conformations in the ground states and their distributions significantly affect the physical properties and device performances. Therefore, professional analysis and a summary of the relationship between molecular structures and performances are very important. In this review, we first summarize the mechanism and properties of TADF emitters with conformational isomerism. We also classify their recent progress according to their different applications, and provide an outlook on their perspectives. [ABSTRACT FROM AUTHOR]

Compared with single-molecule thermally activated delayed fluorescence emitters, exciplexes can simplify the complicated molecule design and synthesis and have the superiority of conveniently realizing spectra with a bathochromic shift via mixing donor and acceptor components. In this work, we develop a series of novel exciplexes with phosphor components showing emission in the range of deep-red to near-infrared (NIR). The phosphor-incorporated exciplexes would improve the utilization of triplet excitons due to the spin–orbit coupling (SOC) effect of heavy metal atoms in phosphors. By employing B2PyMPM, B3PyMPM and B4PyMPM as acceptors, three exciplexes were first constructed with phosphor Ir-817. Optimized B2PyMPM:Ir-817, B3PyMPM:Ir-817 and B4PyMPM:Ir-817-based OLEDs show electroluminescence (EL) peaks at 612, 640 and 672 nm and maximum external quantum efficiencies (EQE) of 3.1%, 1.45% and 1.03%, respectively. To further develop exciplexes with NIR emission, TRZ-1SO2, TRZ-2SO2 and TRZ-3SO2 with stronger electron-withdrawing abilities were chosen as the acceptors. Notably, the TRZ-3SO2:Ir-817-based device exhibits an EL peak at 746 nm and a maximum EQE of 0.20%. These results demonstrate the potential and feasibility of using phosphor-incorporated exciplexes in the development of NIR exciplexes. [ABSTRACT FROM AUTHOR]

Exploiting novel TADF emitters for highly efficient orange-red non-doped organic light-emitting devices (OLEDs) is a research hotspot. Nevertheless, serious non-radiative transitions of the electrogenerated excitons significantly hinder the pace of the development. Herein, two novel donor–π–acceptor (D–π–A) type TADF emitters 10-(4-(2,6-di(pyridin-3-yl)pyrimidin-4-yl)phenyl)-10H-phenoxazine (PyPmP) and 10-(4-(2-(pyridin-3-yl)-[4,5′-bipyrimidin]-6-yl)phenyl)-10H-phenoxazine (PmPmP) were designed and synthesized. In their crystals, suitable intermolecular hydrogen bonding interactions are observed that enable head-against-tail 3D supramolecular frameworks. Such frameworks not only prefer a high horizontal molecular orientation but also strictly restrict the non-radiative process in non-doped conditions. Their non-doped OLEDs realize decent orange-red electroluminescence with maximum current efficiencies (CE), power efficiencies (PE), and external quantum efficiencies (EQE) of 50.5 cd A−1, 53.5 lm W−1, and 18.8% for PyPmP, 23.2 cd A−1, 22.1 lm W−1, and 11.3% for PmPmP, respectively. Moreover, both devices can still retain high efficiencies as luminance increases, and exhibit a neglectable efficiency roll-off at 1000 cd m−2. These results are among the best of ever reported orange-red non-doped OLEDs. These results demonstrate that intermolecular hydrogen bonding interactions can play important roles in exploiting TADF emitters for high-performance orange-red non-doped OLEDs. [ABSTRACT FROM AUTHOR]

Although a variety of electron-accepting molecules (acceptors) have been reported to develop exciplexes, their LUMO energy levels are still limited from −2.9 to −3.3 eV. This narrow range seriously restricts the development of exciplexes. In this work, three novel triazine-based acceptors, 2,4-diphenyl-6-(3-(phenylsulfonyl)phenyl)-1,3,5-triazine (TRZ-1SO2), 2-phenyl-4,6-bis(3-(phenylsulfonyl)phenyl)-1,3,5-triazine (TRZ-2SO2) and 2,4,6-tris(3-(phenylsulfonyl)phenyl)-1,3,5-triazine (TRZ-3SO2), were developed with deep LUMO energy levels of −3.38, −3.58 and −3.74 eV, respectively. Particularly, TRZ-3SO2 exhibits the deepest LUMO energy level of −3.74 eV among the reported acceptors so far. By combining with an electron-donating molecule, 1,3-bis(9,9-dimethylacridin-10(9H)-yl)benzene (13AB), three exciplexes, 13AB:TRZ-1SO2, 13AB:TRZ-2SO2 and 13AB:TRZ-3SO2, were constructed with the emission from green to orange-red. The OLED using 13AB:TRZ-3SO2 as the emitter exhibits an orange-red emission peaking at 572 nm with a maximum external quantum efficiency of 5.5%. Meanwhile, green and red phosphorescent OLEDs (PhOLEDs) were fabricated using interfacial exciplex hosts by combining these acceptors with 4,4′-bis(carbazole-9-yl)biphenyl (CBP), which successfully exhibits superior performance compared with that of reference devices. These results demonstrate that the three novel acceptors have great potential in the development of exciplexes. [ABSTRACT FROM AUTHOR]

A sulfur (S) atom generally undergoes sp3 hybridization when linking two moieties, not only for the sulfane status but also its fully oxidized form, sulfone. In the research reported here an S atom was used as a bridge to construct two thermally activated delayed fluorescence (TADF) emitters, Trz-S-DMAc and Trz-SO2-DMAc. The only difference between these two emitters is the valence of the S atoms in the bridges; however, their electron distributions are greatly affected and the charge-transfer (CT) transitions can be well-modulated between intermolecular and intramolecular modes. In a Trz-S-DMAc molecule, the S atom breaks the conjugation between donor (D) and acceptor (A) moieties, and their CT transition can only then occur with other Trz-S-DMAc molecules. The OLEDs based on Trz-S-DMAc achieve the best external quantum efficiency (EQE) of 18.1% at a high concentration of 55 wt% and maintain a satisfactory EQE of 13.0% for a non-doped device. Whereas for Trz-SO2-DMAc, the sulfone group acts as a second A moiety rather than a simple bridge. The Trz-SO2-DMAc is thus a typical TADF emitter with an effective intramolecular CT transition. The optimized OLED based on Trz-SO2-DMAc achieves a maximum EQE of 18.3%, whereas a significant efficiency drop can be observed with increasing doping concentrations. It is expected that these results will help to increase the understanding of how to link donor and acceptor moieties via sp3 atoms to construct TADF emitters and the roles of the different CT transitions. [ABSTRACT FROM AUTHOR]

High-efficiency orange and red thermally activated delayed fluorescent (TADF) organic light-emitting diodes were fabricated based on a pair of isomers 3,6,11-triAC-BPQ and 3,6,12-triAC-BPQ, containing a rigid dibenzo[f,h]pyrido[2,3-b]quinoxaline (BPQ) core and three 9,9-dimethyl-9,10-dihydroacridine (Ac) donors. Both materials exhibited red emission in neat films and small singlet–triplet energy gaps. Compared with the stable intramolecular charge transfer (ICT) state of 3,6,12-triAC-BPQ, 3,6,11-triAC-BPQ showed hybridized local and charge transfer (HLCT) character due to the H-bond between the 11-position Ac and 10-position N atom. As a result, the doped film of 3,6,11-triAC-BPQ showed a high photoluminescence quantum yield (PLQY) and the related device showed a high external quantum efficiency (EQE) of 22.0% in the orange–red region. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) emitters generally require good separation of highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) overlaps to minimize the singlet–triplet energy offset. Observations of excellent TADF performance in several planar emitters with large HOMO–LUMO overlaps are counter-intuitive and not fully explained. To understand this, we prepared two isomeric TADF molecules, 7-methyl-2-(10H-phenoxazin-10-yl)-5H-pyrano[4,3-b]pyridin-5-one (PXZ-PPO) and 2-methyl-7-(10H-phenoxazin-10-yl)-4H-benzo[d][1,3]oxazin-4-one (PXZ-BOO). PXZ-BOO has a stable highly-twisted configuration with a small HOMO–LUMO overlap leading to good TADF performance as expected. PXZ-PPO has a stable nearly-planar form and a large HOMO–LUMO overlap and is not expected to give TADF. While the solid crystal of PXZ-PPO only shows conventional fluorescence at 420 nm, its diluted solution is dominated by TADF at 610 nm. With a combined experimental and theoretical approach, PXZ-PPO is shown to have a stable nearly-planar form and a metastable highly-twisted form in the ground state. While the highly-twisted form only has a small population (<1%) in the ground state, its excited state has lower energy than the nearly-planar form. As a result, when the high population nearly-planar form is excited, its excited state energy can decay by transforming to the highly-twisted form which shows TADF characteristics. This work points out the importance of low population but energetically stable excited states and explains for the first time the origin of TADF in such nearly-planar emitters with large HOMO–LUMO overlaps. [ABSTRACT FROM AUTHOR]

Exploiting effective orange-red thermally activated delayed fluorescent (TADF) emitters is still challenging. In this work, we proposed a method by using a crooked donor (D) moiety instead of its conventional planar form to balance the opposite influences of frontier molecular orbital overlap on the reverse intersystem crossing and the singlet radiative decay rate. A novel orange-red TADF emitter, named 2-(4-(9,9-dimethyl-4-phenylacridin-10(9H)-yl)phenyl)anthracene-9,10-dione (AQ-PhDMAC), was accordingly designed and synthesized. Owing to the steric effect of the α-phenyl ring in 9,9-dimethyl-4-phenyl-9,10-dihydroacridine (α-PhDMAC), a relatively small singlet–triplet energy splitting of 0.22 eV and a high fluorescence quantum yield of 0.89 can be realized simultaneously. The orange-red organic light-emitting diode based on AQ-PhDMAC exhibited a maximum external quantum efficiency of 18.1%, much improved compared with the 13.7% efficiency of the α-phenyl ring-free control emitter (AQ-DMAC). These results propose a new viewpoint that enforcing crooked D segments by large steric hindrance actually has a great potential for applications in orange-red TADF molecular design, to improve their electroluminescence efficiency. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) emitters normally suffer from serious concentration sensitivity, realizing peak electroluminescence efficiencies with precise control of the doping concentrations, which may hinder their practical applications in organic light emitting devices (OLEDs). In this work, we developed TADF emitter 2′,7′-di(10H-phenoxazin-10-yl)spiro[fluorene-9,9′-thioxanthene]10′,10′-dioxide (SPFS-PXZ) based on conventional TADF emitter 10,10′-(sulfonylbis(4,1-phenylene))bis(10H-phenoxazine) (DPS-PXZ). By introducing a fluorene group, the molecular rigidity and steric hindrance of SPFS-PXZ are improved greatly, which contributes to suppressing the strong π–π stacking tendency between phenoxazine segments and reduces intermolecular interactions. In turn, SPFS-PXZ successfully exhibits low concentration sensitivity in OLEDs, and keeps high maximum external quantum efficiencies (EQEs) over 20.8% with a small EQE fluctuation of 2.1% in a wide doping concentration range from 10 wt% to 50 wt%. These results prove that SPFS-PXZ is an ideal model to develop efficient TADF emitters with low concentration sensitivity. [ABSTRACT FROM AUTHOR]

By introducing two novel electron-donating (D) moieties dibenzothiophene (DBT) and dibenzofuran (DBF) as the secondary D groups, we designed and synthesized four novel blue thermally activated delayed fluorescence (TADF) emitters DBTCz-Trz, DBFCz-Trz, BDBTCz-Trz and BDBFCz-Trz. The secondary DBF and DBT segments all significantly participated in the highest occupied molecular orbital (HOMO) delocalization, resulting in effective TADF characteristics and high photoluminescence quantum yields simultaneously for all four emitters. In the devices, DBTCz-Trz and DBFCz-Trz successfully exhibit identical blue emission with a peak at 472 nm and a CIE coordinate of (0.17, 0.28) in the devices, while BDBTCz-Trz and BDBFCz-Trz exhibit cyan emissions. Moreover, the maximum forward-viewing external quantum efficiencies are determined to be as high as 21.7% for DBTCz-Trz, 21.6% for DBFCz-Trz, 23.4% for BDBTCz-Trz, and 25.1% for BDBFCz-Trz, respectively. These results not only prove the great potential of amine-free electron-donating components such as DBF and DBT in constructing TADF emitters for electroluminescence, but they also reveal the importance of extending the frontier orbital molecular distributions for TADF molecular optimization. [ABSTRACT FROM AUTHOR]

Energy differences (ΔESTs) between the lowest singlet and triplet excited states as well as the oscillator strengths (fs) are two contradictory factors controlling performance of thermally activated delayed fluorescence (TADF) emitters. To figure out their optimum balance, we developed two orange–red isomeric TADF emitters 12-(13,13-dimethyl-5-phenyl-5,13-dihydro-11H-indolo[2,3-b]acridin-11-yl)dibenzo[a,c]dipyrido[3,2-h:2′,3′-j]phenazine (IDAC–BPPZ) and 12-(13,13-dimethyl-11-phenyl-11,13-dihydro-5H-indolo[2,3-b]acridin-5-yl)dibenzo[a,c]dipyrido[3,2-h:2′,3′-j]phenazine (ACID–BPPZ), which are constructed with the same electron-donor (D) and the same electron-acceptor (A) cores via different connecting sites. ACID–BPPZ has a weaker D–A conjugation and realizes an extremely small ΔEST of 0.02 eV, but its f is also very small (0.001). These factors are better compromised in IDAC–BPPZ which has a more conjugated D–A connections. This successfully realizes a much higher f of 0.068 and a reasonably small ΔEST of 0.07 eV. As a result, the orange–red OLEDs using IDAC–BPPZ as emitter achieve a maximum external quantum efficiency 18.3% comparing to that of 14.7% in the ACID–BPPZ-based device. The results suggest that a balance between ΔEST and f is important for developing high performance TADF emitters. [ABSTRACT FROM AUTHOR]

Bacterial infection is posing a great threat to human life, and constructing a platform to capture or kill the bacteria attached on a material surface is of particular significance. Herein, a nano-topographic material surface (SiNW-p-ppix@CDm) has been successfully synthesized based on silicon nanowire (SiNW) arrays modified with a random copolymer, which was decorated with photosensitive protoporphyrin IX (ppix) and β-CD-mannose7 (CDm). The as-prepared surface exhibits a highly efficient bacterial capture, which is based on the co-capture function between the SiNW topographic surface and the bacterial attachment molecule CDm, and sterilization of ppix under irradiation by 630 nm light. The Gram-negative bacterium Escherichia coli (E. coli) was adopted to evaluate the surface bactericidal efficiency. Finally, the killing efficiency can be proved to be 96.7% from fluorescence microscopy after staining with the live/dead bacterial viability kit. The reason for sterilization is that the bacterial cell wall had been split by the reactive oxygen species (ROS), which could be demonstrated via scanning electronic microscopy (SEM). This functional substrate could be used for bacterial enrichment apparatus such as used in water quality monitoring, and even in constructing clinical antibacterial materials. [ABSTRACT FROM AUTHOR]

A novel thermally activated delayed fluorescence (TADF) emitter 1,2,3,4-tetrakis(3,6-di-tert-butyl-9H-carbazol-9-yl)thianthrene 5,5,10,10-tetraoxide (4t-BuCzTTR) was designed and synthesized for solution-processed red organic light-emitting diodes (OLEDs). With appropriate component segments and a well-arranged molecular structure, 4t-BuCzTTR successfully exhibits red fluorescence, significant TADF characteristics, excellent thermal stability and good solution processability. By using 4t-BuCzTTR as the emitter, the optimized doped OLED exhibits an orange-red emission with a peak at 592 nm and a high maximum external quantum efficiency of 6.2%. To the best of our knowledge, the result is not only higher than the theoretical limits of traditional fluorescent OLEDs, but also among the highest results of the reported solution-processed red OLEDs based on pure organic emitters, indicating the superiority of 4t-BuCzTTR. [ABSTRACT FROM AUTHOR]

Photo/chemo combination therapy has been demonstrated to be a generally more powerful strategy for treating cancers than a single treatment modality. However, it is unknown whether the timing of light irradiation has any impact on therapeutic efficacy. We designed a carrier-free and self-monitoring nanodrug to monitor the entire dual-drug release profile and determined the impact of photodynamic therapy (PDT) at different time points. The designed nanodrug consists of the chemotherapeutic doxorubicin (DOX) and the photosensitizer pheophorbide A (PhA). The drugs form a fluorescence resonance energy transfer (FRET) pair (DOX transferring energy to PhA) when present at a precise ratio in the combination nanodrug. Due to the FRET effect, the DOX-PhA nanoparticles (NPs) show PhA fluorescence in a normal pH environment (such as cytoplasm). However, the FRET effect is lost when the NPs are disassembled in an acidic environment (such as lysosomes), and the DOX fluorescence is recovered. By real-time fluorescence variation monitoring, we determined the key time points when the drugs reached various subcellular locations, which helped us to determine the PDT-triggering time points and investigate the impact on the therapeutic effect in the combination therapy. Furthermore, the PDT was triggered at these established time points both in vitro and in vivo, which revealed that the best PDT-triggering time point in the combination therapy was achieved after nuclear entry of DOX. The study suggests that the optimization of combination therapy, not only photo/chemo but also chemo/chemo combination therapy, may require not only a controlled drug ratio but also a controlled drug release profile and target arrival time. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) emitters based on carbazole groups have been reported to realize different efficiencies in devices. Herein, we report two carbazole-based TADF emitters, namely 2-(9H-carbazol-9-yl)thianthrene 5,5,10,10-tetraoxide (CZ-TTR), which has one free-rotation carbazole, and 2,3-di(9H-carbazol-9-yl)thianthrene 5,5,10,10-tetraoxide (DCZ-TTR), which has two mutually restricted carbazole groups, and investigated the influence of steric hindrance on their properties. Both compounds employed the same donor and acceptor segments and connecting mode. However, due to steric hindrance between the two carbazole segments, DCZ-TTR exhibited a smaller singlet–triplet splitting of 0.03 eV compared with that of CZ-TTR (0.10 eV). The device containing DCZ-TTR showed significantly higher efficiencies (20.1% for external quantum efficiency (EQE), 58.5 lm W−1 for power efficiency (PE), and 59.6 cd A−1 for current efficiency (CE)) than those of the CZ-TTR-based device (EQE = 14.4%; PE = 32.9 lm W−1; CE = 32.5 cd A−1). These results clearly proved the necessity of introducing suitable steric hindrance when designing highly efficient TADF emitters based on carbazole groups. [ABSTRACT FROM AUTHOR]

We demonstrate the first systematic study of the diameter-dependent photoelectrochemical performance of single silicon nanowires within a broad size range from 200 to 2000 nm. SiNWs with a diameter of 1415 nm exhibit the highest solar energy conversion efficiency, which can be mainly traced to their diameter-dependent light absorption properties. [ABSTRACT FROM AUTHOR]

A novel nicotinonitrile derivative CZN has been designed with the aim of developing excellent multifunctional blue fluorophores for hybrid white organic light-emitting devices (WOLEDs) by introducing the nicotinonitrile group as the electron acceptor. CZN shows highly efficient blue fluorescence and its non-doped blue OLED delivers an external quantum efficiency (EQE) as high as 4.6%. Meanwhile, CZN is a promising host for phosphorescent OLEDs, realizing high EQEs of 22.8%, 24.8% and 19.9% for yellow, orange and deep-red phosphorescence, respectively. By using CZN as the blue emitter and the host simultaneously, a hybrid white OLED has been achieved with a forward-viewing EQE of 17.2%. These results indicate that the nicotinonitrile unit is an excellent building block for developing new multifunctional compounds as both blue fluorescent emitters and phosphorescent hosts for efficient hybrid WOLEDs. [ABSTRACT FROM AUTHOR]

A new efficient blue fluorophor 4-(4-diphenylaminophenyl)diphenylsulfone (SOTPA), with high triplet energy and balanced charge-transporting properties, has been designed and synthesized, and showed impressive performance both as blue emitter and as a host for phosphors. A green phosphorescent device containing SOTPA as host showed a maximum external quantum efficiency (EQE) as high as 19.2%, suggesting almost complete triplet harvesting from the blue fluorophor by the green phosphor. Single-emitting layer (EML) F–P hybrid white organic light-emitting devices (WOLEDs) based on SOTPA also gave outstanding electroluminescence performance, with a low turn-on voltage of 2.7 V and maximum EQE and power efficiency (PE) of 15.4% and 40.2 lm W−1, respectively. Even at a practical brightness of 1000 cd m−2 the PE still remained as high as 24.1 lm W−1. This excellent performance represents the highest efficiency yet reported among single-EML F–P hybrid WOLEDs. [ABSTRACT FROM AUTHOR]

Three terpyridine (TPY)/diphenylamine (DPA) derivatives, with DPA functioning as the electron donor and TPY as the electron acceptor, were designed and synthesized. By switching the position of the nitrogen atom in the substituted pyridine of TPY acceptors, we can adjust the electron-drawing strength of the TPY group, and hence, further modify the fluorescence, lowest unoccupied molecular orbital energy levels, carrier transporting properties of three compounds, but barely influence triplet energy levels. Three compounds satisfy the requirements of multifunctional blue fluorophores and are successfully used as highly efficient blue fluorescent emitters and red phosphorescent hosts in organic light-emitting devices (OLEDs). Non-doped blue fluorescent OLEDs that use TPY22DPA, TPY33DPA, and TPY44DPA as emitters exhibit maximum external quantum efficiencies (EQEs) of 4.9%, 3.8%, and 2.7%, respectively. Meanwhile, red phosphorescent OLEDs that use TPY22DPA, TPY33DPA, and TPY44DPA as host materials exhibit maximum EQEs of 19.1%, 20.9%, and 17.2%, respectively. These results are among the best reported multifunctional blue fluorophore efficiencies. [ABSTRACT FROM AUTHOR]

Heavy-metal-free, organic-small-molecule-based fluorescent nanodots (Sdots, 31–60 nm in diameter) based on 2,7-di(4-(diphenylamino)phenyl-2,1,3-benzothiadiazol-7-yl)-9,9′-spirobifluorene (Spiro-BTA) were prepared through a simple solution process. The Sdots show not only non-blinking and high-brightness fluorescence but also stability in various pH conditions and heavy metal ion solutions. More importantly, Spiro-BTA Sdots demonstrate obviously much higher brightness with very high signal-to-background ratio in Hela cell, compared with common CdSe/ZnS QDs. In addition, they exhibit large Stokes shifts, broad absorption spectra, and low toxicity to living cells which enable their applications as good fluorescence probes for bio-imaging. Further application of Sdots for folate receptor-mediated live-cell endocytosis was demonstrated by non-convalent modification with folic acid linked multidentate ligands. [ABSTRACT FROM AUTHOR]

Electron-accepting solution-processable conjugated polymers consisting of perylene diimide moieties alternating with dithienothiophene, oligo(dithienothiophene), or N-dodecyl dithienopyrrole units have been synthesized. All these polymers possess excellent thermal stability with decomposition temperatures over 400 °C. The glass-transition temperatures vary from 155 to 263 °C. These polymers show broad absorption extending from 250 to 900 nm with electrochemical and optical bandgaps as low as 1.4 eV; the maximum absorbance increases and the bandgap decreases with increasing the conjugation length of oligo(dithienothiophene), while the bandgap can also be decreased by the replacement of dithienothiophene by dithienopyrrole. The electrochemical onset reduction potentials range from −0.8 to −1.0 V vs.ferrocenium/ferrocene, suggesting that the electron affinities are essentially unaffected by the specific choice of donor moiety, while the onset oxidation potentials (+0.6 to +1.0 V) are a little more sensitive to the choice of donor. The mono dithienothiophene and the dithienopyrrole polymers were found to exhibit electron mobilities as high as 1.3 × 10−2and 1.2 × 10−3cm2V−1s−1, respectively, in top-contact organic field-effect transistors. Power conversion efficiencies in the range 0.77–1.1% were obtained under simulated AM 1.5, 100 mW/cm2irradiation for all-polymer solar cells using the dithienothiophene-based polymers as acceptors in a 1 : 1 ratio with a polythiophene derivative as a donor. The device performance varies with the conjugation length of oligo(dithienothiophene) in the polymer acceptors, and for the best-performing material it can be further optimized to give a power conversion efficiency of 1.5% by increasing the donor/acceptor weight ratio to 3 : 1. [ABSTRACT FROM AUTHOR]

Tin (Sn with 5% of Si by weight) can be used as a liquid substrate to fabricate ZnO/SiO2hierarchical nanostructures and self-assemble these three-dimensional nanostructures into a vertical array at the same time. [ABSTRACT FROM AUTHOR]

Exciplex emitters naturally have thermally activated delayed fluorescence characteristics due to their spatially separated molecular orbitals. However, the intermolecular charge transfer potentially induces diverse non-radiative decay channels, severely hindering the construction of efficient red exciplexes. Thus, a thorough comprehension of this energy loss is of paramount importance. Herein, different factors, including molecular rigidity, donor-acceptor interactions and donor-donor/acceptor-acceptor interactions, that impact the non-radiative decay were systematically investigated using contrasting exciplex emitters. The exciplex with rigid components and intermolecular hydrogen bonds showed a photoluminescence quantum yield of 84.1% and a singlet non-radiative decay rate of 1.98 × 10 6 s -1 at an optimized mixing ratio, respectively, achieving a 3.3-fold increase and a 70% decrease compared to the comparison group. In the electroluminescent device, a maximum external quantum efficiency of 23.8% was achieved with an emission peak of 608 nm, which represents the state-of-the-art organic light-emitting diodes using exciplex emitters. Accordingly, a new strategy is finally proposed, exploiting system rigidification to construct efficient red exciplex emitters that suppress non-radiative decay., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Atomically separated frontier molecular orbital (FMO) distribution plays a crucial role in achieving narrowband emissions for multiple resonance (MR)-type thermally activated delayed fluorescence emitters. Directly peripherally decorating a MR framework with donor or acceptor groups is a common strategy for developing MR emitters. However, this approach always induces bonding features and thus spectral broadening as a side effect. How direct donor/acceptor decoration enhances atomic FMO separation while avoiding bonding features has not been explored. For this aim, two MR derivatives are synthesized by integrating two MR frameworks at different sites. Following resonance alignment, DOBNA- m -CzBN avoids breaking nonbonding FMO features at the single connecting bond and shows enhanced MR characteristics, with a sharp emission at 491 nm and a full width at half maximum (FWHM) of 24 nm/118 meV. Conversely, DOBNA- p -CzBN emerges as a bonding feature due to its continuous π-conjugation extension, with a broadened FWHM of 26 nm/132 meV peaking at 497 nm. Impressively, both emitters exhibit outstanding external quantum efficiencies of 37.8-38.6% in organic light-emitting diodes (OLEDs), demonstrating improved performance with rigid acceptor decoration. Distinctly, the electroluminescence of DOBNA- m -CzBN shows a narrower FWHM than that of DOBNA- p -CzBN. This work for the first time reports the enhancement of atomic FMO separation for MR emitters via peripheral decoration through a single bond and provides a more comprehensive illustration for further development of MR emitters.

Thermally activated delayed fluorescence (TADF) emitters with aggregation-induced emission (AIE) features are hot candidates for non-doped organic light-emitting diodes (OLEDs), as they are highly emissive in solid states upon photoexcitation. Nevertheless, not every AIE-TADF emitter in the past had guaranteed decent efficiencies in non-doped devices, indicating that the AIE character alone does not necessarily afford ideal non-doped TADF emitters. As intermolecular electron-exchange interaction that involves long-lived triplet excitons plays a dominant role in the whole quenching process of TADF, we anticipate that it is the main reason for the different electroluminescence performances of AIE-TADF emitters. Therefore, in this work, we designed two TADF emitters SPBP-DPAC and SPBP-SPAC by modifying a reported less successful emitter BP-DPAC with extra fluorenes to increase intermolecular distances and attenuate this electron-exchange interaction. With the fluorene lock as steric hindrance, SPBP-DPAC and SPBP-SPAC exhibit significantly higher exciton utilization in non-doped films due to the suppressed concentration quenching. The non-doped OLEDs based on SPBP-DPAC and SPBP-SPAC show an excellent maximum external quantum efficiency (EQE) of 22.8% and 21.3% respectively, and what's even more promising is that ignorable roll-offs at practical brightness ( e.g. , 1000 and 5000 cd m -2 ) were realized. These results reveal that locking the phenyl rings as steric hindrance can not only enhance the molecular rigidity, but also cause immediate relief of concentration quenching, and result in significant performance improvement under non-doped conditions. Our approach proposes a feasible molecular modification strategy for AIE-TADF emitters, potentially increasing their applicability in OLEDs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Rational manipulation of energy utilization from excited-state radiation of theranostic agents with a donor-acceptor structure is relatively unexplored. Herein, we present an effective strategy to tune the exciton dynamics of radiative excited state decay for augmenting two-photon nanotheranostics. As a proof of concept, two thermally activated delayed fluorescence (TADF) molecules with different electron-donating segments are engineered, which possess donor-acceptor structures and strong emissions in the deep-red region with aggregation-induced emission characteristics. Molecular simulations demonstrate that change of the electron-donating sections could effectively regulate the singlet-triplet energy gap and oscillator strength, which promises efficient energy flow. A two-photon laser with great permeability is used to excite TADF NPs to perform as theranostic agents with singlet oxygen generation and fluorescence imaging. These unique performances enable the proposed TADF emitters to exhibit tailored balances between two-photon singlet oxygen generation and fluorescence emission. This result demonstrates that TADF emitters can be rationally designed as superior candidates for nanotheranostic agents by the custom controlling exciton dynamics., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

A Pd-catalyzed C(sp2)-H aminocarbonylation of aryl carboxamides assisted by an N,S-bidentate directing group was developed, in which cheap and stable sodium trifluoromethanesulfinate was first utilized as a carbonyl source. The reaction can be applicable to a wide range of carboxamides with good functional group tolerance and afford isoindole-1,3-diones in moderate to good yields.

A novel phosphine oxide-diphenylamine hybrid compound POA was designed and synthesized with the aim of developing new multifunctional blue fluorophores. POA is the first kind of compound that can be used as a high-efficiency deep-blue emitter (5.4% EQE) and a host to fabricate high-performance green phosphorescent OLEDs (18.1% EQE).

Recently, bipolar host materials have attracted considerable attention because they can achieve balanced charge injection/transport in phosphorescent organic light emitting diodes (PhOLEDs) and consequently obtain excellent device performance. In this work, two bipolar host materials, namely, 3-(4,6-diphenyl-1,3,5-triazin-2-yl)-9-phenyl-9H-carbazole (DPTPCz) and 3-(4,6-diphenoxy-1,3,5-triazin-2-yl)-9-phenyl-9H-carbazole (DPOTPCz), have been designed, synthesized and characterized. With high triplet energy levels of 2.78 and 2.86 eV for DPTPCz and DPOTPCz, respectively, two compounds are considered promising bipolar host materials for PhOLEDs. Blue and green PhOLEDs based on these two new compounds show excellent performances. The phosphorescent devices based on DPTPCz exhibit maximum external quantum efficiencies of 14.4% (for blue device) and 21.2% (for green device), and maintain high efficiencies of 11.9% and 20.0% even at a high luminance of 10,000 cd m(-2).

A controllable method for coating a dense layer of poly-CuTAPc polymer on the surface of silicon nanowire array was reported and it is shown that the coating of poly-CuTAPc can effectively enhance both the photocatalytic hydrogen generation efficiency and the operation stability., (This journal is © The Royal Society of Chemistry 2012)

Tin (Sn with 5% of Si by weight) can be used as a liquid substrate to fabricate ZnO/SiO(2) hierarchical nanostructures and self-assemble these three-dimensional nanostructures into a vertical array at the same time.