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Charge-transfer (CT) state is becoming a useful excited state to design next-generation luminescence materials for high-performance organic light-emitting diode (OLED). However, strong CT state usually causes serious decrease in photoluminescence (PL) efficiency due to the small overlap between HOMO and LUMO. In order to harvest both high exciton utilization and high PL efficiency in fluorescent OLEDs, figuring out the strategy of fine modification of CT component in excited state through structural modulation is important. In this work, four donor–acceptor structure triphenylamine (TPA) - acridine (AC) isomers (TPA-9AC, TPA-1AC, TPA-2AC and TPA-3AC) were designed and synthesized to investigate structure-property relationship between isomerization effect and excited state properties. Density functional theory (DFT) calculations and solvatochromic absorption, emission and photoluminescence decay spectra are carried out for the deep understanding of their emissive state character. The four isomers exhibit gradually increased PL efficiency from low-polarity hexane to medium-polarity tetrahydrofuran (THF), which could be assigned to the formation of hybridized local and charge-transfer (HLCT) states and effectively suppressed non-radiative transition arised from acridine in medium-polarity solvents. Among four isomers, TPA-3AC achieved the best EL performance, due to the proper LE and CT compositions in the emissive state, demonstrating that isomerization of donor and acceptor functional moieties is an effective approach for structural modification for high-efficiency fluorescent OLED emitters. [ABSTRACT FROM AUTHOR]

Developing highly efficient red emitters with emission beyond 600 nm is full of challenges for organic light-emitting diodes (OLEDs). Herein, two novel red isomers of 11-DTPA-BBI and 3-DTPA-BBI manifesting hybridized local and charge-transfer (HLCT) state were designed and synthesized, based on triphenylamine (TPA) as donor and 7H-benzo[ de ]benzo[4,5]imidazo[2,1- a ]isoquinolin-7-one (BBI) as acceptor. The charge-transfer (CT) component in HLCT state ensures their red emission and high excitons utilization, while the locally excited (LE) component guarantees the high fluorescence radiative rate. Further, the non-radiative transition is suppressed through regulating molecular vibration modes by isomer engineering, resulting in the high fluorescence quantum efficiency of 53% for 3-DTPA-BBI. Consequently, a maximum external quantum efficiency of 3.0% is achieved with emission peak at 604 nm in 3-DTPA-BBI based OLEDs. This contribution demonstrates a comprehensive structure-property relationship which may provide an effective guidance to design high performance red electroluminescent emitters. [Display omitted] • A quasi-equivalent HLCT status is acquired with balanced LE and CT components. • The non-radiative vibrations are largely suppressed by interactional TPA donors. • 3-DTPA-BBI based device achieves high EQE of 3.0% with red emission at 604 nm. [ABSTRACT FROM AUTHOR]

The abnormal change of lipid droplets (LDs) polarity has been believed to be closely associated with many diseases such as fatty liver. Thus, the detection of LDs polarity plays a particular role in the diagnosis of LDs polarity-related diseases. Herein, two isoindole-based fluorescent probes have been derived and they show evident solvatochromic effects, large two-photon absorption cross-section, LDs-specificity, and high photostability and excellent performance in monitoring LDs-polarity changes in living cells. Owing to the existence of intramolecular charge transfer process, these isoindole-based probes exhibited high sensitivity between the emission wavelength maxima and solvent polarity. In spite of that, they maintained high fluorescence quantum yields up to 0.87. Moreover, the detection of LDs-polarity was demonstrated in living cells via confocal laser scanning fluorescence imaging. Importantly, the isoindole-based probe maintained strong fluorescence with high contrast and clarity after seven days of degradation in a zebrafish model, indicating that it is photostable enough and suitable for long-term tracking and observation of biological dynamic changes. All these features render the isoindole chromophore an effective implement for the diagnosis of LDs polarity-related diseases. Two isoindole-based fluorescent probes have been derived and they show evident solvatochromic effects, LDs-specificity, large two-photon absorption cross-section, and high photostability and excellent performance in monitoring LDs-polarity changes in living cells. [Display omitted] [ABSTRACT FROM AUTHOR]

Developing probes for selective and sensitive detection of hydrogen sulfide (H 2 S) has received much research attention, because H 2 S is an environmental toxin as well as an important signaling molecule to regulate physiological and pathological processes. In this work, a new colorimetric and ratiometric fluorescent probe (Probe 1) for H 2 S detection was synthesized by employing dicyanoisophorone based fluorescence dye as a fluorophore and azide group as the response unit. The synthesized Probe 1 showed a long emission wavelength ( λ em = 643 nm) and large stokes shift ( λ em − λ abs = 163 nm). Based on the H 2 S-induced reduction of azide group to amino group, Probe 1 showed high response speed, sensitivity, and selectivity toward HS − under room temperature. Moreover, Probe 1 can ratiometrically respond to HS − and the detection limit is as low as 0.13 μM. It was proved that Probe 1 is suitable for quantitatively detecting HS − ions in river water samples. The numerous advantages of Probe 1 make it be potentially used for quantitative detection of H 2 S in environment and living organisms. [ABSTRACT FROM AUTHOR]

The synthesis of near-infrared emitting BODIPY fluorophore is a key requirement for biomedical imaging applications. Herein, a series of non-symmetric benzothieno[7,6- b ]-fused BODIPY dyes were efficiently synthesized. All of them have been well characterized by NMR (1H, 13C, 11B, 19F), HRMS, UV–vis, Emission, and X-ray crystal analysis. These dyes exhibit effective planar expansion of π-conjugation on the BODIPY core. The absorption from 540 to 700 nm and emission from 620 to 780 nm are effectively tuned by benzothieno[7,6- b ] fusion or Knoevenagel condensation reaction. More importantly, these developed dyes showed high specificity for staining lipid droplets. Cell imaging experiments demonstrated that a benzothieno[7,6- b ]-fused BODIPY with para -dimethylaminophenyl group exhibited high photo-stability for imaging in living cell. The synthesis and functional modification for the benzothieno[7,6- b ]-fused BODIPY dye provided an effective way for generating BODIPY-based near-infrared dyes in medical and biological applications. Novel non-symmetric benzothieno[7,6- b ]-fused BODIPYs with NIR emission were synthesized, which showed high specificity for staining lipid droplets and high photo-stability in living cell. [Display omitted] [ABSTRACT FROM AUTHOR]

Until now the photopolymerization process is largely dependent on the hazardous UV or near UV light irradiation. Herein this work, a series of boron dipyrromethene (BODIPY) derivatives substituted by electron-donating triphenylamine moiety on different positions were introduced and investigated thoroughly. Markedly, their photoinitiation abilities under mild conditions, e.g. visible LEDs irradiation and room temperature, were examined for the first time. In combination with an iodonium salt and an amine as the co-initiators, these BODIPY dyes could form three-component photoinitiating systems (PISs) for the purpose to initiate both the free radical polymerization of acrylate monomers and cationic polymerization of epoxy monomers. Interestingly, under the irradiation of LED@405 nm, LED@530 nm or LED@660 nm, some of these BODIPYs-based PISs could conduct high monomeric conversion and rapid photopolymerization rates, as reflected by the relevant photopolymerization kinetics. Then the notable photochemical reactivity of these BODIPY dyes was examined by both steady state photolysis and fluorescence quenching experiments, and theoretical calculation was also performed on them in details. Finally, photocuring 3D printing technique was applied to the acrylate/epoxy mixture resin, as the result the BODIPYs-based PISs demonstrated great potential to fabricate truly three-dimensional objects in macroscopic scale with excellent spatial resolution. [Display omitted] • Five BODIPY derivatives containing the triphenylamine moiety were introduced as promising photoinitiators. • Visible LEDs (405 nm, 530 nm and 660 nm) were used as the irradiation source. • Both of free radical polymerization and cationic polymerization can be initiated by the BODIPY dyes. • 3D patterns were successfully printed through the photopolymerization of interpenetrating polymer network (IPN). [ABSTRACT FROM AUTHOR]

Subcellular organelle-specific probes, including mitochondria-targeted fluorescent probes, have attracted enormous research interests because they can monitor or visualize the morphology or biological activities of specific organelles and play an indispensable role in disease diagnosis. To follow the process, highly specific and photostable fluorescent probes are in demand. However, commercially available mitochondria probes normally suffer from poor photostability under laser irradiation and aggregation caused quenching (ACQ) in the aggregate state. In this work, two simple aggregation-induced emission(AIE)-active meso -2-ketopyrrolyl BODIPYs were developed via a convenient one-pot synthetic procedure from 2-methylpyrrole and corresponding pyrrolyldiketone in the presence of BF 3 ·OEt 2. The two AIE luminogens (AIEgens) both show very weak fluorescence (maximum emission peaks at 545 and 559 nm, respectively) in DMSO and strong near-infrared solid-state emission. The fluorescence was dramatically intensified and redshifted to 635 and 643 nm, respectively, when water fraction was increased up to above 95% in the DMSO/water mixtures. Both AIEgens were found to specifically "light up" the cell mitochondria with high biocompatibility. Interestingly, the staining process can be shortened for less than a minute after the addition of the AIEgens and without the involvement of a washing procedure, indicating an ultrafast and easy-to-operate staining protocol. Furthermore, their fluorescent images in deep tissue penetration were captured with a satisfied signal-to-noise ratio at a depth of 20 and 30 μm along the direction of the z-axis. Importantly, both AIEgens exhibit high photostability under harsh continuous laser irradiation, demonstrating their potential application as in visualizing and tracking specific mitochondria-associated dynamic changes. Two mitochondria specific red-emissive BODIPY AIEgens have been developed for fluorescent imaging and deep tissue imaging, which exhibit ultrafast and easy-to-operate staining, wash-free bioimaging and high photostability. Image 1 [ABSTRACT FROM AUTHOR]

Abnormal changes in numbers, sizes and polarities of lipid droplet (LD) are thought to be closely associated with varieties diseases such as fatty liver, diabetes, atherosclerosis and even cancer. However, there still exists some shortcomings of the current commercial LD probes, such as aggregation-caused quenching (ACQ) effect, small Stokes shifts, excitation wavelength restricted to visible light region, and lacking of two-photon excitation fluorescence, which restrict the diagnosis of LD related diseases. Herein, a two-photon aggregation-induced emission (AIE) bioprobe, namely TP-LDP, was rationally designed by constructing of the donor-acceptor-donor (D-A-D) structure for specific imaging of LD. TP-LDP exhibited AIE-activities, solvatochromic emissions (λ em max: 451–652 nm), extra-large Stokes shifts (11550 cm−1) as well as two-photon absorption ability (156 GM). More importantly, cellular experiments demonstrated that TP-LDP possessed excellent photostability, nice two-photon excited fluorescence imaging ability as well as precise LD-targeting, and successfully detected abnormal LD proliferations in living cells. These features enable TP-LDP to effectively compensate for the shortcomings of commercial LD dyes and have the potential to become a powerful tool for detecting LD related diseases. [Display omitted] • A novel fluorescent dye is constructed based on acrylonitrile structure. • This dye exhibits strong solvatochromic emissions and ultra large Stoke shifts as well as aggregation-induced emission (AIE). • This dye has good photostability and two-photon imaging capability. • The AIE dye is suitable for fluorescence bio-imaging and can specifically localize in lipid droplets of cells. [ABSTRACT FROM AUTHOR]

The development of blue phosphorescent iridium(III) complexes has been a formidable challenge in the field of organic light-emitting diodes (OLEDs). Unlike the conventional blue Ir-complex structure of symmetric tri -/ bis -cyclometalated coordination geometry, we herein report a new configuration of [Ir(C 1 ^N 1)(C 2 ^N 2)(LX)]- tris -heteroleptic Ir(III) complex, where C 1 ^N 1 and C 2 ^N 2 denote two different main ligands, and LX stands for a third ancillary ligand. By the new configuration, two asymmetric blue iridium complexes, namely dfbpy-Ir-dfppy and dfppy-Ir-dfbpy, were designed and synthesized, displaying the highly desirable blue emission peaks at 450 nm and 452 nm, respectively. Based on the two new emitters, the blue OLEDs exhibited good performances with the maximum external quantum efficiency (EQE max) reaching 8.5% and CIE(x, y) coordinates of (0.21, 0.31). This study provides a new strategy for efficient blue iridium complexes through reasonably engineering the asymmetric tris -heteroleptic Ir-complex configuration. [Display omitted] • Two blue isomers possessing the asymmetric tris -heteroleptic [Ir(C 1 ^N 1)(C 2 ^N 2)(LX)]- configuration and their application in OLEDs were rarely reported. • The pure blue emission bands centered around 450 nm, and short lifetimes of 1.67- 3.26 μs. • The blue PHOLED displayed good performances. [ABSTRACT FROM AUTHOR]

Fusion thiophene to BODIPY endows the chromophore with more fundamental and special functions. Herein, novel symmetric bisbenzothieno[ b ]-fused BODIPYs (BTBs) were synthesized and developed. These newly prepared BTB dyes possessed absorption maxima in the range of 643–665 nm, and many outstanding properties including large molar extinction coefficients, and high singlet oxygen generation. Theoretical calculations affirmed that the smaller singlet-triplet energy gap and larger spin−orbit coupling result in efficient intersystem crossing, thus increasing the singlet oxygen generation yield. Notably, Me 2 NPh-substituted BTB displayed good reactive oxygen species generation efficiency up to 0.41, and a remarkable photo-cytotoxicity (IC 50 = 83.5 nM) in HeLa cells, which shows potential in low-dose photodynamic therapy. Novel bisbenzothieno[ b ]-fused BODIPYs (BTBs) were developed as efficient near-infrared heavy-atom-free photosensitizers, which show strong absorption maxima up to 665 nm, good reactive oxygen species generation efficiency up to 0.41, and remarkable photo-cytotoxicity (IC 50 = 83.5 nM) in HeLa cells. [Display omitted] • Novel bisbenzothieno[ b ]-fused BODIPYs were developed as efficient near-infrared heavy-atom-free photosensitizers. [ABSTRACT FROM AUTHOR]

A novel copper-catalyzed direct acylation of BODIPYs with aldehydes via C–H bond activation was developed, in which acyl radicals were formed from aldehydes in the presence of TBHP as radical initiator, and selectively reacted with BODIPYs at the α-positions. This radical oxidative dehydrogenative cross-coupling reaction showed excellent functional group tolerance, and both heteroaromatic and aliphatic aldehydes could be effectively reacted to BODIPYs. Comparing with those of the corresponding starting BODIPYs, those α-acylated BODIPYs showed red-shifted absorption and emission, as well as decreased both HOMO and LUMO energies due to the installation of electron-deficient carbonyl groups. Furthermore, the α-acylated BODIPY provided an efficient access to α-acylated dipyrrin by removal of the BF 2 protecting groups, which showed sensitive and selective "turn-on" fluorescence response toward Zn2+ ion in aqueous buffer solution and living cells. Copper-catalyzed direct acylation of BODIPYs with aldehydes regioselectively provides structurally diverse α-acylated BODIPYs via radical pathway. [Display omitted] • A novel copper-catalyzed direct acylation of BODIPYs with aldehydes via C–H bond activation has been developed. • Various mono- and di-α-acylated BODIPYs were synthesized and showed tunable photophysical properties. • α-Acylated dipyrrin was obtained by removal of the BF 2 group of di-α-acylated BODIPY. • α-Acylated dipyrrin showed sensitive and selective "turn-on" fluorescence response toward Zn2+ ion. [ABSTRACT FROM AUTHOR]

A series of boronic acid derived salicylidenehydrazinopyridine complexes have been synthesized from the condensation of 2-hydrazinopyridine or 2-hydrazinoquinoline and salicylaldehyde then followed by complexation with various boronic acids. Their X-ray structures demonstrate that the boron atoms adopt a tetrahedral geometry and the aryl substituents from arylboric acids along the vertical axis gave the molecule stereotactic structure and induced molecular chirality. These dyes have good solubility on organic solvents due to the nonplanar curved structure and the presence of axial-substituted groups that provide steric protection. They have strong visible-light absorption, weak emission and large Stoke shifts in organic solvents. Interestingly, molecular aggregates of these new boron complexes experienced the transformation from H -type aggregation to J- type aggregation and exhibited strong aggregation-induced emission (AIE) activities. These novel AIE dyes showed great potential as bioimaging dyes, and two complexes were mainly distributed in lipid droplets of cells in colocalization experiments. [Display omitted] • New boron complexed fluorophore (BOSPY) has been developed from various arylboric acids. • Molecular chirality of these dyes after boron complexation was confirmed by X-ray structures. • These dyes exhibit strong aggregation-induced emission (AIE). • These AIE dyes are suitable for fluorescence imaging and two dyes can specifically localize in lipid droplets of cells. [ABSTRACT FROM AUTHOR]

As one of the main atmospheric pollutants, sulfur dioxide (SO 2 ) can be easily inhaled and turned into sulfite and bisulfite, which is harmful to both human health and ecological environment. Therefore, it is of significance to develop an effective method to detect the trace SO 2 derivatives—SO 3 2− and HSO 3 − . Herein, we synthesized a semi-cyanine-coumarin hybrid dye for detection of SO 3 2− and HSO 3 − . Based on the nucleophilic addition of HSO 3 − /SO 3 2− to the vinyl group, Probe 1 showed high response speed, selectivity, and sensitivity towards SO 3 2− and HSO 3 − . Upon addition of HSO 3 − /SO 3 2− , color obviously changes from blue to yellow which can be differentiated by naked eyes. Probe 1 displays colorimetric and ratiometric response toward HSO 3 − and SO 3 2− . The detection limit is as low as 27.6 nM and the signal-to-background ratio in fluorescence intensity can reach 35-folds. Moreover, Probe 1 showed high selectivity and anti-interference ability in the co-existence of the environmental and biologic species. [ABSTRACT FROM AUTHOR]

In this work, two novel D-π-A compounds (PXZ-FR-DRZ and CZ-FR-DRZ) are designed and synthesized, aiming at the excited-state regulation from thermally-activated delayed fluorescence (TADF) to hybridized local and charge-transfer (HLCT) emission. This change of excited-state nature can be ascribed to the weakened electron-donating ability of carbazole relative to phenoxazine, together with the decreased twisting angle between carbazole and fluorine units. As a result of twisted charge-transfer (CT) excited state, the doped organic light-emitting diode (OLED) of PXZ-FR-DRZ demonstrates a blue-green TADF electroluminescence (EL) with a maximum external quantum efficiency (EQE max) of 11.5%, while its non-doped device shows a much lower EQE max. Due to HLCT state of CZ-FR-DRZ , both its doped and non-doped OLEDs achieve the deep-blue non-delayed EL with the satisfied external quantum efficiency (EQE), especially for the excellent efficiency roll-off. Overall, this excited-state transformation between TADF and HLCT allows us to harvest the better comprehensive performance of OLED emitters for the practical applications, which provides a feasible solution for the development of OLED industry. Two different donors (phenoxazine and carbazole) are designed to match the same acceptor of 2,4-diphenyl-1,3,5-triazine (DRZ) through a π-bridged linkage of 9,9-dimethyl-9H-fluorene (FR), resulting in two novel D-π-A molecules of PXZ-FR-DRZ and CZ-FR-DRZ , respectively. The PXZ-FR-DRZ realizes a blue-green thermally-activated delayed fluorescence (TADF) with high external quantum efficiency (EQE) in the doped organic light-emitting diodes (OLEDs) due to the twisted charge-transfer (CT) excited state, whereas the CZ-FR-DRZ achieves a deep-blue non-doped OLED with the better comprehensive performance as a result of the hybridized local and charge-transfer (HLCT) state. [Display omitted] • Two D-π-A materials CZ-FR-DRZ and PXZ-FR-DRZ are synthesized with HLCT and TADF properties respectively. • The TADF PXZ-FR-DRZ exhibits higher EQE than CZ-FR-DRZ. • As an HLCT material, CZ-FR-DRZ displays high performance in non-doped OLED. • The conversion between HLCT and TADF is investigated by changing different donors. [ABSTRACT FROM AUTHOR]

High performance blue emitters with nice color purity are highly desired in the commercialization of organic light-emitting diodes (OLEDs). Herein, two blue-emissive hybridized local and charge-transfer (HLCT) phenanthroimidazole (PPI) derivatives were designed and synthesized. Comparing to the 9,9-dimethyl-9,10-dihydroacridine (DMAC) substituted DPCN , the 10H-spiro[acridine-9,9′-fluorene] (SAF) substituted SPCN demonstrates higher photoluminescence quantum yield (PLQY) and improved radiative transition rate (k r). With the same device structure, despite that SPCN and DPCN show similar electroluminescence (EL) spectra, the EL efficiency of SPCN is about 1.5 times that of DPCN. Especially the non-doped OLED based on SPCN , the maximum external quantum efficiency (EQE) is 7.1%, which is a competitive result among the conventional blue-emissive fluorescent emitters. More importantly, this work provides a general strategy to achieve high performance blue/deep-blue OLED by rational donor optimization. In this work, we report two blue-emissive hybridized local and charge-transfer (HLCT) materials (DPCN and SPCN) with different donor substitution. Comparing to the 9,9-dimethyl-9,10-dihydroacridine (DMAC) substituted DPCN , the 10H-spiro[acridine-9,9′-fluorene] (SAF) substituted SPCN displays an improved EL efficiency and blue purity, which provides an ideal molecular design strategy for efficient blue/deep-blue EL materials. [Display omitted] • Two blue-emissive HLCT materials with different donor substitution were designed and synthesized. • The relationship of structure-physical property as well as OLED performance are comprehensively explored. • Comparing to DPCN, the SAF substituted SPCN achieved a better OLED performance. [ABSTRACT FROM AUTHOR]

The development of the thermally activated delayed fluorescence (TADF) emitters with circularly polarized luminescence (CPL), particularly those exhibiting deep-blue emission is still a formidable challenge. In this work, we reported a simple and easily accessed molecular design strategy for deep-blue circularly polarized TADF (CP-TADF) enantiomers. Two chiral compounds, namely (S)-NPE-AcDPS and (R)-NPE-AcDPS, were successfully designed and synthesized, which featured concurrently TADF, CPL, and aggregation-induced enhanced emission (AIEE) properties. The CPL exhibited a maximum g PL value of 3.0 × 10−4. These emitters exhibited deep blue emission peaking at 451 nm in doped film with a high photoluminescence of 86% and a small singlet-triplet splitting of 0.05 eV. Furthermore, the deep blue OLED based on (S)-NPE-AcDPS demonstrated a high external quantum efficiency (EQE) up to 18.5%. [Display omitted] • Rigidifying the two phenyls of the famous emitter DMAC-DPS with a chiral bridge unit resulted in two blue TADF emitters. • The emitters exhibited high photoluminescence quantum yields, excellent TADF properties and obvious chiroptical activities. • Deep-blue TADF organic light-emitting diodes achieved external quantum efficiency of up to 18.5%. [ABSTRACT FROM AUTHOR]

Simultaneously achieving both effective reverse intersystem crossing (RISC) process and high values of radiative decay rate (k r)/photoluminescent quantum yield (PLQY) are critical for efficient thermally activated delayed fluorescent (TADF) emitters. The separation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) through typical molecular geometry tuning method guarantees a small Δ E ST but results in disfavored oscillator strength for fluorescent decay. Herein, a simple method is provided to facilitate the reverse intersystem crossing (RISC) of TADF emitters via enhancing electron donating property of donors rather than twisting the donor-acceptor configuration. Three molecules, namely Me-Cz, Me-MOC and Me-DOC, are designed and synthesized. The introduction of methoxy group enhances the electron-donating ability of carbazole. The stabilized charge transfer state features a reduced splitting energy between the first singlet and triplet excited state, thus activating TADF process. Consequently, the molecules Me-DOC and Me-MOC achieve good external quantum efficiency of 18.6% and 12.4% in electroluminescent devices. Image 1 • Two thermally activated delayed fluorescent (TADF) emitters constructed by solely carbazole as donor. • Efficient TADF-OLED with external quantum efficiency up to 18.6%. • Activating TADF process via enhancing electron donating properties of donor. [ABSTRACT FROM AUTHOR]

Based on novel phenanthro[9,10- d imidazole (PI) chromophore, three deep-blue luminescent donor-acceptor molecules with different molecular configurations at the triphenylamine (TPA) core were designed and synthesized, the linear TPA-1PI, the V-shaped TPA-2PI and the star-shaped TPA-3PI. All three molecules displayed the hybridized local and charge-transfer (HLCT) excited state character, and highly efficient deep blue emissions were observed in their solution state, but only those of linear TPA-1PI and V-shaped TPA-2PI molecule were maintained in the solid state. Meanwhile, the V-shaped TPA-2PI and star-shaped TPA-3PI showed the much better thermal properties. Thus the molecular configurations of HLCT materials significantly influence their solid-state, and the V-shaped TPA-2PI molecule was highlighted because of its both deep-blue emission and good thermal stability. A double-layer device by using TPA-2PI as the emitter showed a highly efficient deep-blue electroluminescence with a very good CIE coordinate of (0.14, 0.08) and high current efficiency of 2.7 cd A−1, which suggest that it might be a promising candidate for emission-layer materials for high-performance deep-blue OLEDs. Image 1 • Three high efficiency blue emission benzimidazole derivatives were synthesized. • Different configurations compounds in linear, V and star-shape were analyzed. • All of the three compounds have hybridized local and charge-transfer properties. • TPA-2PI based OLED show deep blue emission with CIE (0.14, 0.08) and EQE max = 2.6%. [ABSTRACT FROM AUTHOR]

A novel halogen bond-based co-crystal, 4,4′-trimethylenedipyridine/1,4-diiodotetrafluorobenzene (TMDP-DITFB), was achieved, which displays distinct piezochromic luminescence from none to a broad emission band (500–700 nm) assigned to the new intermolecular charge transfer (CT) state caused by the enhanced I⋯N interactions between TMDP and DITFB. Interestingly, once the pressure was released to the ambient condition, the emission of TMDP-DITFB could not be restored to initial state, but exhibited a new red maximum emission band at 668 nm, which is different from most piezochromic materials. Almost no change for the TMDP crystal was observed during the compression-decompression cycle. Comparative analysis between TMDP and TMDP-DITFB demonstrates that irreversible changes in fluorescence are highly related to intermolecular interactions between TMDP and co-formers modulated by pressure. Pressure-induced enhanced and irreversible emission of organic materials is rarely reported. This work enables deeper understanding on the structure-property relationship and put forward a new strategy to realize new properties of materials. Image 1 • A TMDP-DITFB co-crystal is obtained via intermolecular I⋯N interactions. • Intermolecular charge transfer brings TMDP-DITFB remarkable pressure-induced emission enhancement. • TMDP-DITFB exhibits irreversible emission during compression-decompression process. [ABSTRACT FROM AUTHOR]

Three host materials, DCzPh , DCzPy and DCzPm , were developed for phosphorescent organic light emitting devices (PhOLEDs). These three compounds exhibit high triplet energy level (E T > 2.7 eV), suitable glass transition temperatures (T g > 130 °C), appropriate highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, and balanced charge-transporting properties. Green PhOLEDs were fabricated by utilizing these three materials as hosts and the efficiencies were satisfactory. Device G3 based on DCzPm exhibited high efficiency with the maximum external quantum efficiency (EQE) of 17.2%, and even at the brightness of 1000 cd m−2, the EQE reached 17.1%, demonstrating its low efficiency roll-off. The above results indicate that these host materials possess great commercial potential in OLED applications. Image 1 • Three bipolar host materials DCzPh , DCzPy and DCzPm were designed and synthesized. • The above three hosts exhibit good thermal stability with T g > 130 °C. • DCzPm- based green PhOLED exhibits excellent performance with maximum EQE of 17.2%. [ABSTRACT FROM AUTHOR]